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  • XNA 2D Collision with specific tiles

    - by zenzero
    I am new to game programming and to these sites for help. I am making a 2D game but I can't seem to get the collision between my character and certain tiles. I have a map filled with grass tiles and water tiles and I want to keep my character from walking on the water tiles. I have a Tiles class that I use so that the tiles are objects and also has the collision method in it, a TileEngine class used create the map and it also holds a list of Tiles, and the class James which is for my character. I also have a Camera class that centers the camera on my character if that has anything to do with the problem. The character's movement is intended to be restricted to 4 directions(up, down, left, right). As an extra note, the bottom right water tile does have collision, but the collision does not occur for any of the other water tiles. Here is my TileEngine class using System; using System.Collections.Generic; using System.Linq; using Microsoft.Xna.Framework; using Microsoft.Xna.Framework.Audio; using Microsoft.Xna.Framework.Content; using Microsoft.Xna.Framework.GamerServices; using Microsoft.Xna.Framework.Graphics; using Microsoft.Xna.Framework.Input; using Microsoft.Xna.Framework.Media; namespace Test2DGame2 { class TileEngine : Microsoft.Xna.Framework.Game { //makes a list of Tiles objects public List<Tiles> tilesList = new List<Tiles>(); public TileEngine() {} public static int tileWidth = 64; public static int tileHeight = 64; public int[,] map = { {0, 0, 0, 0, 0, 0, 0, 0, 0, 0, 0, 0, 0, 0, 0, 0, 0, 0, 0, 0, 0, }, {0, 0, 0, 0, 0, 0, 0, 0, 0, 1, 0, 1, 0, 0, 0, 0, 0, 0, 0, 0, 0, }, {0, 0, 0, 0, 0, 0, 0, 0, 0, 1, 0, 1, 0, 0, 0, 0, 0, 0, 0, 0, 0,}, {0, 0, 0, 0, 0, 0, 0, 0, 0, 1, 0, 1, 0, 0, 0, 0, 0, 0, 0, 0, 0,}, {0, 0, 0, 0, 0, 1, 1, 1, 1, 1, 0, 1, 1, 1, 1, 0, 0, 0, 0, 0, 0,}, {0, 0, 0, 0, 0, 1, 0, 0, 0, 0, 0, 0, 0, 0, 1, 0, 0, 0, 0, 0, 0,}, {0, 0, 0, 0, 0, 1, 0, 0, 0, 0, 0, 0, 0, 0, 1, 0, 0, 0, 0, 0, 0,}, {0, 0, 0, 0, 0, 1, 0, 0, 0, 0, 1, 0, 0, 0, 1, 0, 0, 0, 0, 0, 0,}, {0, 0, 0, 0, 0, 1, 0, 0, 0, 0, 0, 0, 0, 0, 1, 0, 0, 0, 0, 0, 0,}, {0, 0, 0, 0, 0, 1, 0, 0, 0, 0, 0, 0, 0, 0, 1, 0, 0, 0, 0, 0, 0,}, {0, 0, 0, 0, 0, 1, 0, 0, 0, 0, 0, 0, 0, 0, 1, 0, 0, 0, 0, 0, 0,}, {0, 0, 0, 0, 0, 1, 0, 0, 0, 0, 0, 0, 0, 0, 1, 0, 0, 0, 0, 0, 0,}, {0, 0, 0, 0, 0, 1, 0, 0, 0, 0, 0, 0, 0, 0, 1, 0, 0, 0, 0, 0, 0,}, {0, 0, 0, 0, 0, 1, 0, 0, 0, 0, 0, 0, 0, 0, 1, 0, 0, 0, 0, 0, 0,}, {0, 0, 0, 0, 0, 1, 0, 0, 0, 0, 0, 0, 0, 0, 1, 0, 0, 0, 0, 0, 0,}, {0, 0, 0, 0, 0, 1, 0, 0, 0, 0, 0, 0, 0, 0, 1, 0, 0, 0, 0, 0, 0,}, {0, 0, 0, 0, 0, 1, 0, 0, 0, 0, 0, 0, 0, 0, 1, 0, 0, 0, 0, 0, 0,}, {0, 0, 0, 0, 0, 1, 0, 0, 0, 0, 0, 0, 0, 0, 1, 0, 0, 0, 0, 0, 0,}, {0, 0, 0, 0, 0, 1, 1, 1, 1, 1, 1, 1, 1, 1, 1, 0, 0, 0, 0, 0, 0,}, {0, 0, 0, 0, 0, 0, 0, 0, 0, 0, 0, 0, 0, 0, 0, 0, 0, 0, 0, 0, 0,}, {0, 0, 0, 0, 0, 0, 0, 0, 0, 0, 0, 0, 0, 0, 0, 0, 0, 0, 0, 0, 0,}, {0, 0, 0, 0, 0, 0, 0, 0, 0, 0, 0, 0, 0, 0, 0, 0, 0, 0, 0, 0, 0,}, }; public void drawMap(SpriteBatch spriteBatch) { for (int y = 0; y < map.GetLength(0); y++) { for (int x = 0; x < map.GetLength(1); x++) { //make a Rectangle tilesList[map[y, x]].rectangle = new Rectangle(x * tileWidth, y * tileHeight, tileWidth, tileHeight); //draw the Tiles objects spriteBatch.Draw(tilesList[map[y, x]].texture, tilesList[map[y, x]].rectangle, Color.White); } } } } } Here is my Tiles class using System; using System.Collections.Generic; using System.Linq; using Microsoft.Xna.Framework; using Microsoft.Xna.Framework.Audio; using Microsoft.Xna.Framework.Content; using Microsoft.Xna.Framework.GamerServices; using Microsoft.Xna.Framework.Graphics; using Microsoft.Xna.Framework.Input; using Microsoft.Xna.Framework.Media; namespace Test2DGame2 { class Tiles { public Texture2D texture; public Rectangle rectangle; public Tiles(Texture2D texture) { this.texture = texture; } //check to see if james collides with the tile from the right side public void rightCollision(James james) { if (james.GetBounds().Intersects(rectangle)) { james.position.X = rectangle.Left - james.front.Width; } } } } I have a method for rightCollision because I could only figure out how to get the collisions from specifying directions. and here is the James class for my character using System; using System.Collections.Generic; using System.Linq; using Microsoft.Xna.Framework; using Microsoft.Xna.Framework.Audio; using Microsoft.Xna.Framework.Content; using Microsoft.Xna.Framework.GamerServices; using Microsoft.Xna.Framework.Graphics; using Microsoft.Xna.Framework.Input; using Microsoft.Xna.Framework.Media; namespace Test2DGame2 { class James { public Texture2D front; public Texture2D back; public Texture2D left; public Texture2D right; public Vector2 center; public Vector2 position; public James(Texture2D front) { position = new Vector2(0, 0); this.front = front; center = new Vector2(front.Width / 2, front.Height / 2); } public James(Texture2D front, Vector2 newPosition) { this.front = front; position = newPosition; center = new Vector2(front.Width / 2, front.Height / 2); } public void move(GameTime gameTime) { KeyboardState keyboard = Keyboard.GetState(); float SCALE = 20.0f; float speed = gameTime.ElapsedGameTime.Milliseconds / 100.0f; if (keyboard.IsKeyDown(Keys.Up)) { position.Y -=speed * SCALE; } else if (keyboard.IsKeyDown(Keys.Down)) { position.Y += speed * SCALE; } else if (keyboard.IsKeyDown(Keys.Left)) { position.X -= speed * SCALE; } else if (keyboard.IsKeyDown(Keys.Right)) { position.X += speed * SCALE; } } public void draw(SpriteBatch spriteBatch) { spriteBatch.Draw(front, position, null, Color.White, 0, center, 1.0f, SpriteEffects.None, 0.0f); } //get the boundingbox for James public Rectangle GetBounds() { return new Rectangle( (int)position.X, (int)position.Y, front.Width, front.Height); } } }

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  • Spritesheet per pixel collision XNA

    - by Jixi
    So basically i'm using this: public bool IntersectPixels(Rectangle rectangleA, Color[] dataA,Rectangle rectangleB, Color[] dataB) { int top = Math.Max(rectangleA.Top, rectangleB.Top); int bottom = Math.Min(rectangleA.Bottom, rectangleB.Bottom); int left = Math.Max(rectangleA.Left, rectangleB.Left); int right = Math.Min(rectangleA.Right, rectangleB.Right); for (int y = top; y < bottom; y++) { for (int x = left; x < right; x++) { Color colorA = dataA[(x - rectangleA.Left) + (y - rectangleA.Top) * rectangleA.Width]; Color colorB = dataB[(x - rectangleB.Left) + (y - rectangleB.Top) * rectangleB.Width]; if (colorA.A != 0 && colorB.A != 0) { return true; } } } return false; } In order to detect collision, but i'm unable to figure out how to use it with animated sprites. This is my animation update method: public void AnimUpdate(GameTime gameTime) { if (!animPaused) { animTimer += (float)gameTime.ElapsedGameTime.TotalMilliseconds; if (animTimer > animInterval) { currentFrame++; animTimer = 0f; } if (currentFrame > endFrame || endFrame <= currentFrame || currentFrame < startFrame) { currentFrame = startFrame; } objRect = new Rectangle(currentFrame * TextureWidth, frameRow * TextureHeight, TextureWidth, TextureHeight); origin = new Vector2(objRect.Width / 2, objRect.Height / 2); } } Which works with multiple rows and columns. and how i call the intersect: public bool IntersectPixels(Obj me, Vector2 pos, Obj o) { Rectangle collisionRect = new Rectangle(me.objRect.X, me.objRect.Y, me.objRect.Width, me.objRect.Height); collisionRect.X += (int)pos.X; collisionRect.Y += (int)pos.Y; if (IntersectPixels(collisionRect, me.TextureData, o.objRect, o.TextureData)) { return true; } return false; } Now my guess is that i have to update the textureData everytime the frame changes, no? If so then i already tried it and miserably failed doing so :P Any hints, advices? If you need to see any more of my code just let me know and i'll update the question. Updated almost functional collisionRect: collisionRect = new Rectangle((int)me.Position.X, (int)me.Position.Y, me.Texture.Width / (int)((me.frameCount - 1) * me.TextureWidth), me.Texture.Height); What it does now is "move" the block up 50%, shouldn't be too hard to figure out. Update: Alright, so here's a functional collision rectangle(besides the height issue) collisionRect = new Rectangle((int)me.Position.X, (int)me.Position.Y, me.TextureWidth / (int)me.frameCount - 1, me.TextureHeight); Now the problem is that using breakpoints i found out that it's still not getting the correct color values of the animated sprite. So it detects properly but the color values are always: R:0 G:0 B:0 A:0 ??? disregard that, it's not true afterall =P For some reason now the collision area height is only 1 pixel..

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  • Collision between sprites in game programming?

    - by Lyn Maxino
    I've since just started coding for an android game using eclipse. I've read Beginning Android Game Programming and various other e-books. Recently, I've encountered a problem with collision between sprites. I've used this code template for my program. package com.project.CAI_test; import java.util.Random; import android.graphics.Bitmap; import android.graphics.Canvas; import android.graphics.Rect; public class Sprite { // direction = 0 up, 1 left, 2 down, 3 right, // animation = 3 back, 1 left, 0 front, 2 right int[] DIRECTION_TO_ANIMATION_MAP = { 3, 1, 0, 2 }; private static final int BMP_ROWS = 4; private static final int BMP_COLUMNS = 3; private static final int MAX_SPEED = 5; private GameView gameView; private Bitmap bmp; private int x = 0; private int y = 0; private int xSpeed; private int ySpeed; private int currentFrame = 0; private int width; private int height; public Sprite(GameView gameView, Bitmap bmp) { this.width = bmp.getWidth() / BMP_COLUMNS; this.height = bmp.getHeight() / BMP_ROWS; this.gameView = gameView; this.bmp = bmp; Random rnd = new Random(); x = rnd.nextInt(gameView.getWidth() - width); y = rnd.nextInt(gameView.getHeight() - height); xSpeed = rnd.nextInt(MAX_SPEED * 2) - MAX_SPEED; ySpeed = rnd.nextInt(MAX_SPEED * 2) - MAX_SPEED; } private void update() { if (x >= gameView.getWidth() - width - xSpeed || x + xSpeed <= 0) { xSpeed = -xSpeed; } x = x + xSpeed; if (y >= gameView.getHeight() - height - ySpeed || y + ySpeed <= 0) { ySpeed = -ySpeed; } y = y + ySpeed; currentFrame = ++currentFrame % BMP_COLUMNS; } public void onDraw(Canvas canvas) { update(); int srcX = currentFrame * width; int srcY = getAnimationRow() * height; Rect src = new Rect(srcX, srcY, srcX + width, srcY + height); Rect dst = new Rect(x, y, x + width, y + height); canvas.drawBitmap(bmp, src, dst, null); } private int getAnimationRow() { double dirDouble = (Math.atan2(xSpeed, ySpeed) / (Math.PI / 2) + 2); int direction = (int) Math.round(dirDouble) % BMP_ROWS; return DIRECTION_TO_ANIMATION_MAP[direction]; } public boolean isCollition(float x2, float y2) { return x2 > x && x2 < x + width && y2 > y && y2 < y + height; } } The above code only detects collision between the generated sprites and the surface border. What I want to achieve is a collision detection that is controlled by the update function without having to change much of the coding. Probably several lines placed in the update() function. Tnx for any comment/suggestion.

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  • Problems with moving 2D circle/box collision detection

    - by dario3004
    This is my first game ever and I'm a newbie in computer physics. I've got this code for the collision detection and it works fine for BOTTOM and TOP collision.It miss the collision detection with the paddle's edge and angles so I've (roughly) tried to implement it. Main method that is called for bouncing, it checks if it bounce with wall, or with top (+ right/left side) or with bottom (+ right/left side): protected void handleBounces(float px, float py) { handleWallBounce(px, py); if(mBall.y < getHeight()/4){ if (handleRedFastBounce(mRed, px, py)) return; if (handleRightSideBounce(mRed,px,py)) return; if (handleLeftSideBounce(mRed,px,py)) return; } if(mBall.y > getHeight()/4 * 3){ if (handleBlueFastBounce(mBlue, px, py)) return; if (handleRightSideBounce(mBlue,px,py)) return; if (handleLeftSideBounce(mBlue,px,py)) return; } } This is the code for the BOTTOM bounce: protected boolean handleRedFastBounce(Paddle paddle, float px, float py) { if (mBall.goingUp() == false) return false; // next position tx = mBall.x; ty = mBall.y - mBall.getRadius(); // actual position ptx = px; pty = py - mBall.getRadius(); dyp = ty - paddle.getBottom(); xc = tx + (tx - ptx) * dyp / (ty - pty); if ((ty < paddle.getBottom() && pty > paddle.getBottom() && xc > paddle.getLeft() && xc < paddle.getRight())) { mBall.x = xc; mBall.y = paddle.getBottom() + mBall.getRadius(); mBall.bouncePaddle(paddle); playSound(mPaddleSFX); increaseDifficulty(); return true; } else return false; } As long as I understood it should be something like this: So I tried to make the "left side" and "right side" bounce method: protected boolean handleLeftSideBounce(Paddle paddle, float px, float py){ // next position tx = mBall.x + mBall.getRadius(); ty = mBall.y; // actual position ptx = px + mBall.getRadius(); pty = py; dyp = tx - paddle.getLeft(); yc = ty + (pty - ty) * dyp / (ptx - tx); if (ptx < paddle.getLeft() && tx > paddle.getLeft()){ System.out.println("left side bounce1"); System.out.println("yc: " + yc + "top: " + paddle.getTop() + " bottom: " + paddle.getBottom()); if (yc > paddle.getTop() && yc < paddle.getBottom()){ System.out.println("left side bounce2"); mBall.y = yc; mBall.x = paddle.getLeft() - mBall.getRadius(); mBall.bouncePaddle(paddle); playSound(mPaddleSFX); increaseDifficulty(); return true; } } return false; } I think I'm quite near to the solution but I'm having big troubles with the new "yc" formula. I tried so many versions of it but since I don't know the theory behind it I can't adjust for the Y axis. Since the Y axis is inverted I even tried this: yc = ty - (pty - ty) * dyp / (ptx - tx); I tried Googling it but I can't seem to find a solution for it. Also this method fails when ball touches the angle and I don't think is a nice way because it just test "one" point of the ball and probably there will be many cases in which the ball won't bounce.

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  • AABB vs OBB Collision Resolution jitter on corners

    - by patt4179
    I've implemented a collision library for a character who is an AABB and am resolving collisions between AABB vs AABB and AABB vs OBB. I wanted slopes for certain sections, so I've toyed around with using several OBBs to make one, and it's working great except for one glaring issue; The collision resolution on the corner of an OBB makes the player's AABB jitter up and down constantly. I've tried a few things I've thought of, but I just can't wrap my head around what's going on exactly. Here's a video of what's happening as well as my code: Here's the function to get the collision resolution (I'm likely not doing this the right way, so this may be where the issue lies): public Vector2 GetCollisionResolveAmount(RectangleCollisionObject resolvedObject, OrientedRectangleCollisionObject b) { Vector2 overlap = Vector2.Zero; LineSegment edge = GetOrientedRectangleEdge(b, 0); if (!SeparatingAxisForRectangle(edge, resolvedObject)) { LineSegment rEdgeA = new LineSegment(), rEdgeB = new LineSegment(); Range axisRange = new Range(), rEdgeARange = new Range(), rEdgeBRange = new Range(), rProjection = new Range(); Vector2 n = edge.PointA - edge.PointB; rEdgeA.PointA = RectangleCorner(resolvedObject, 0); rEdgeA.PointB = RectangleCorner(resolvedObject, 1); rEdgeB.PointA = RectangleCorner(resolvedObject, 2); rEdgeB.PointB = RectangleCorner(resolvedObject, 3); rEdgeARange = ProjectLineSegment(rEdgeA, n); rEdgeBRange = ProjectLineSegment(rEdgeB, n); rProjection = GetRangeHull(rEdgeARange, rEdgeBRange); axisRange = ProjectLineSegment(edge, n); float axisMid = (axisRange.Maximum + axisRange.Minimum) / 2; float projectionMid = (rProjection.Maximum + rProjection.Minimum) / 2; if (projectionMid > axisMid) { overlap.X = axisRange.Maximum - rProjection.Minimum; } else { overlap.X = rProjection.Maximum - axisRange.Minimum; overlap.X = -overlap.X; } } edge = GetOrientedRectangleEdge(b, 1); if (!SeparatingAxisForRectangle(edge, resolvedObject)) { LineSegment rEdgeA = new LineSegment(), rEdgeB = new LineSegment(); Range axisRange = new Range(), rEdgeARange = new Range(), rEdgeBRange = new Range(), rProjection = new Range(); Vector2 n = edge.PointA - edge.PointB; rEdgeA.PointA = RectangleCorner(resolvedObject, 0); rEdgeA.PointB = RectangleCorner(resolvedObject, 1); rEdgeB.PointA = RectangleCorner(resolvedObject, 2); rEdgeB.PointB = RectangleCorner(resolvedObject, 3); rEdgeARange = ProjectLineSegment(rEdgeA, n); rEdgeBRange = ProjectLineSegment(rEdgeB, n); rProjection = GetRangeHull(rEdgeARange, rEdgeBRange); axisRange = ProjectLineSegment(edge, n); float axisMid = (axisRange.Maximum + axisRange.Minimum) / 2; float projectionMid = (rProjection.Maximum + rProjection.Minimum) / 2; if (projectionMid > axisMid) { overlap.Y = axisRange.Maximum - rProjection.Minimum; overlap.Y = -overlap.Y; } else { overlap.Y = rProjection.Maximum - axisRange.Minimum; } } return overlap; } And here is what I'm doing to resolve it right now: if (collisionDetection.OrientedRectangleAndRectangleCollide(obb, player.PlayerCollision)) { var resolveAmount = collisionDetection.GetCollisionResolveAmount(player.PlayerCollision, obb); if (Math.Abs(resolveAmount.Y) < Math.Abs(resolveAmount.X)) { var roundedAmount = (float)Math.Floor(resolveAmount.Y); player.PlayerCollision._position.Y -= roundedAmount; } else if (Math.Abs(resolveAmount.Y) <= 30.0f) //Catch cases where the player should be able to step over the top of something { var roundedAmount = (float)Math.Floor(resolveAmount.Y); player.PlayerCollision._position.Y -= roundedAmount; } else { var roundedAmount = (float)Math.Floor(resolveAmount.X); player.PlayerCollision._position.X -= roundedAmount; } } Can anyone see what might be the issue here, or has anyone experienced this before that knows a possible solution? I've tried for a few days to figure this out on my own, but I'm just stumped.

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  • Bounding Box Collision Glitching Problem (Pygame)

    - by Ericson Willians
    So far the "Bounding Box" method is the only one that I know. It's efficient enough to deal with simple games. Nevertheless, the game I'm developing is not that simple anymore and for that reason, I've made a simplified example of the problem. (It's worth noticing that I don't have rotating sprites on my game or anything like that. After showing the code, I'll explain better). Here's the whole code: from pygame import * DONE = False screen = display.set_mode((1024,768)) class Thing(): def __init__(self,x,y,w,h,s,c): self.x = x self.y = y self.w = w self.h = h self.s = s self.sur = Surface((64,48)) draw.rect(self.sur,c,(self.x,self.y,w,h),1) self.sur.fill(c) def draw(self): screen.blit(self.sur,(self.x,self.y)) def move(self,x): if key.get_pressed()[K_w] or key.get_pressed()[K_UP]: if x == 1: self.y -= self.s else: self.y += self.s if key.get_pressed()[K_s] or key.get_pressed()[K_DOWN]: if x == 1: self.y += self.s else: self.y -= self.s if key.get_pressed()[K_a] or key.get_pressed()[K_LEFT]: if x == 1: self.x -= self.s else: self.x += self.s if key.get_pressed()[K_d] or key.get_pressed()[K_RIGHT]: if x == 1: self.x += self.s else: self.x -= self.s def warp(self): if self.y < -48: self.y = 768 if self.y > 768 + 48: self.y = 0 if self.x < -64: self.x = 1024 + 64 if self.x > 1024 + 64: self.x = -64 r1 = Thing(0,0,64,48,1,(0,255,0)) r2 = Thing(6*64,6*48,64,48,1,(255,0,0)) while not DONE: screen.fill((0,0,0)) r2.draw() r1.draw() # If not intersecting, then moves, else, it moves in the opposite direction. if not ((((r1.x + r1.w) > (r2.x - r1.s)) and (r1.x < ((r2.x + r2.w) + r1.s))) and (((r1.y + r1.h) > (r2.y - r1.s)) and (r1.y < ((r2.y + r2.h) + r1.s)))): r1.move(1) else: r1.move(0) r1.warp() if key.get_pressed()[K_ESCAPE]: DONE = True for ev in event.get(): if ev.type == QUIT: DONE = True display.update() quit() The problem: In my actual game, the grid is fixed and each tile has 64 by 48 pixels. I know how to deal with collision perfectly if I moved by that size. Nevertheless, obviously, the player moves really fast. In the example, the collision is detected pretty well (Just as I see in many examples throughout the internet). The problem is that if I put the player to move WHEN IS NOT intersecting, then, when it touches the obstacle, it does not move anymore. Giving that problem, I began switching the directions, but then, when it touches and I press the opposite key, it "glitches through". My actual game has many walls, and the player will touch them many times, and I can't afford letting the player go through them. The code-problem illustrated: When the player goes towards the wall (Fine). When the player goes towards the wall and press the opposite direction. (It glitches through). Here is the logic I've designed before implementing it: I don't know any other method, and I really just want to have walls fixed in a grid, but move by 1 or 2 or 3 pixels (Slowly) and have perfect collision without glitching-possibilities. What do you suggest?

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  • Collision Handling in Javascript - Particles Get Stuck

    - by Conner Ruhl
    I am trying to recreate this, and I have been fairly successful. I am having issues with the collision handling though. Although the collision handling seems to work, it has very strange behavior. Here is what I have so far. This is the code that handles collisions: var dx = particle2.getX() - particle1.getX(); var dy = particle2.getY() - particle1.getY(); var angle = Math.atan2(dy, dx); var newP2X = particle1.getX() + (particle1.getRadius() + particle2.getRadius()) * Math.cos(angle); var newP2Y = particle1.getY() + (particle1.getRadius() + particle2.getRadius()) * Math.sin(angle); particle2.setX(newP2X); particle2.setY(newP2Y); var p1Vxi = particle1.getVx(); var p1Vyi = particle1.getVy(); var p1Mass = particle1.getMass(); var p2Vxi = particle2.getVx(); var p2Vyi = particle2.getVy(); var p2Mass = particle2.getMass(); var vxf = (p1Mass * p1Vxi + p2Mass * p2Vxi) / (p1Mass + p2Mass); var vyf = (p1Mass * p1Vyi + p2Mass * p2Vyi) / (p1Mass + p2Mass); particle1.setVx(vxf); particle1.setVy(vyf); particle2.setVx(vxf); particle2.setVy(vyf); EDIT: I have tried to change it to inelastic collisions like suggested, but for some reason the balls collide erratically. Check it out here. Any help is much appreciated!

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  • Collision Detection Code Structure with Sloped Tiles

    - by ProgrammerGuy123
    Im making a 2D tile based game with slopes, and I need help on the collision detection. This question is not about determining the vertical position of the player given the horizontal position when on a slope, but rather the structure of the code. Here is my pseudocode for the collision detection: void Player::handleTileCollisions() { int left = //find tile that's left of player int right = //find tile that's right of player int top = //find tile that's above player int bottom = //find tile that's below player for(int x = left; x <= right; x++) { for(int y = top; y <= bottom; y++) { switch(getTileType(x, y)) { case 1: //solid tile { //resolve collisions break; } case 2: //sloped tile { //resolve collisions break; } default: //air tile or whatever else break; } } } } When the player is on a sloped tile, he is actually inside the tile itself horizontally, that way the player doesn't look like he is floating. This creates a problem because when there is a sloped tile next to a solid square tile, the player can't move passed it because this algorithm resolves any collisions with the solid tile. Here is a gif showing this problem: So what is a good way to structure my code so that when the player is inside a sloped tile, solid tiles get ignored?

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  • Coarse Collision Detection in highly dynamic environment

    - by Millianz
    I'm currently working a 3D space game with A LOT of dynamic objects that are all moving (there is pretty much no static environment). I have the collision detection and resolution working just fine, but I am now trying to optimize the collision detection (which is currently O(N^2) -- linear search). I thought about multiple options, a bounding volume hierarchy, a Binary Spatial Partitioning tree, an Octree or a Grid. I however need some help with deciding what's best for my situation. A grid seems unfeasible simply due to the space requirements and cache coherence problems. Since everything is so dynamic however, it seems to be that trees aren't ideal either, since they would have to be completely rebuilt every frame. I must admit I never implemented a physics engine that required spatial partitioning, do I indeed need to rebuild the tree every frame (assuming that everything is constantly moving) or can I update the trees after integrating? Advice is much appreciated - to give some more background: You're flying a space ship in an asteroid field, and there are lots and lots of asteroids and some enemy ships, all of which shoot bullets. EDIT: I came across the "Sweep an Prune" algorithm, which seems like the right thing for my purposes. It appears like the right mixture of fast building of the data structures involved and detailed enough partitioning. This is the best resource I can find: http://www.codercorner.com/SAP.pdf If anyone has any suggestions whether or not I'm going in the right direction, please let me know.

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  • Collision detection, stop gravity

    - by Scott Beeson
    I just started using Gamemaker Studio and so far it seems fairly intuitive. However, I set a room to "Room is Physics World" and set gravity to 10. I then enabled physics on my player object and created a block object to match a platform on my background sprite. I set up a Collision Detection event for the player and the block objects that sets the gravity to 0 (and even sets the vspeed to 0). I also put a notification in the collision event and I don't get that either. I have my key down and key up events working well, moving the player left and right and changing the sprites appropriately, so I think I understand the event system. I must just be missing something simple with the physics. I've tried making both and neither of the objects "solid". Pretty frustrating since it looks so easy. The player starting point is directly above the block object in the grid and the player does fall through the block. I even made the block sprite solid red so I could see it (initially it was invisible, obviously).

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  • 2D Side scroller collision detection

    - by Shanon Simmonds
    I am trying to do some collision detection between objects and tiles, but the tiles do not have there own x and y position, they are just rendered to the x and y position given, there is an array of integers which has the ids of the tiles to use(which are given from an image and all the different colors are assigned different tiles) int x0 = camera.x / 16; int y0 = camera.y / 16; int x1 = (camera.x + screen.width) / 16; int y1 = (camera.y + screen.height) / 16; for(int y = y0; y < y1; y++) { if(y < 0 || y >= height) continue; // height is the height of the level for(int x = x0; x < x1; x++) { if(x < 0 || x >= width) continue; // width is the width of the level getTile(x, y).render(screen, x * 16, y * 16); } } I tried using the levels getTile method to see if the tile that the object was going to advance to, to see if it was a certain tile, but, it seems to only work in some directions. Any ideas on what I'm doing wrong and fixes would be greatly appreciated. What's wrong is that it doesn't collide properly in every direction and also this is how I tested for a collision in the objects class if(!level.getTile((x + xa) / 16, (y + ya) / 16).isSolid()) { x += xa; y += ya; } EDIT: xa and ya represent the direction as well as the movement, if xa is negative it means the object is moving left, if its positive it is moving right, and same with ya except negative for up, positive for down.

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  • Change collision action

    - by PatrickR
    I have a collision detection and its working fine, the problem is, that whenever my "bird" is hitting a "cloud", the cloud dissapers and i get some points. The same happens for the "sol" which it should, but not with the clouds. How can this be changed ? ive tryed a lot, but can seem to figger it out. Collision Code - (void)update:(ccTime)dt { bird.position = ccpAdd(bird.position, skyVelocity); NSMutableArray *projectilesToDelete = [[NSMutableArray alloc] init]; for (CCSprite *bird in _projectiles) { bird.anchorPoint = ccp(0, 0); CGRect absoluteBox = CGRectMake(bird.position.x, bird.position.y, [bird boundingBox].size.width, [bird boundingBox].size.height); NSMutableArray *targetsToDelete = [[NSMutableArray alloc] init]; for (CCSprite *cloudSprite in _targets) { cloudSprite.anchorPoint = ccp(0, 0); CGRect absoluteBox = CGRectMake(cloudSprite.position.x, cloudSprite.position.y, [cloudSprite boundingBox].size.width, [cloudSprite boundingBox].size.height); if (CGRectIntersectsRect([bird boundingBox], [cloudSprite boundingBox])) { [targetsToDelete addObject:cloudSprite]; } } for (CCSprite *solSprite in _targets) { solSprite.anchorPoint = ccp(0, 0); CGRect absoluteBox = CGRectMake(solSprite.position.x, solSprite.position.y, [solSprite boundingBox].size.width, [solSprite boundingBox].size.height); if (CGRectIntersectsRect([bird boundingBox], [solSprite boundingBox])) { [targetsToDelete addObject:solSprite]; score += 50/2; [scoreLabel setString:[NSString stringWithFormat:@"%d", score]]; } } // NÅR SKYEN BLIVER RAMT AF FUGLEN for (CCSprite *cloudSprite in targetsToDelete) { //[_targets removeObject:cloudSprite]; //[self removeChild:cloudSprite cleanup:YES]; } // NÅR SOLEN BLIVER RAMT AF FUGLEN for (CCSprite *solSprite in targetsToDelete) { [_targets removeObject:solSprite]; [self removeChild:solSprite cleanup:YES]; } if (targetsToDelete.count > 0) { [projectilesToDelete addObject:bird]; } [targetsToDelete release]; } // NÅR FUGLEN BLIVER RAMT AF ALT ANDET for (CCSprite *bird in projectilesToDelete) { //[_projectiles removeObject:bird]; //[self removeChild:bird cleanup:YES]; } [projectilesToDelete release]; }

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  • Collision checking problem on a Tiled map

    - by nosferat
    I'm working on a pacman styled dungeon crawler, using the free oryx sprites. I've created the map using Tiled, separating the floor, walls and treasure in three different layers. After importing the map in libGDX, it renders fine. I also added the player character, for now it just moves into one direction, the player cannot control it yet. I wanted to add collision and I was planning to do this by checking if the player's new position is on a wall tile. Therefore as you can see in the following code snippet, I get the tile type of the appropriate tile and if it is not zero (since on that layer there is nothing except the wall tile) it is a collision and the player cannot move further: final Vector2 newPos = charController.move(warrior.getX(), warrior.getY()); if(!collided(newPos)) { warrior.setPosition(newPos.x, newPos.y); warrior.flip(charController.flipX(), charController.flipY()); } [..] private boolean collided(Vector2 newPos) { int row = (int) Math.floor((newPos.x / 32)); int col = (int) Math.floor((newPos.y / 32)); int tileType = tiledMap.layers.get(1).tiles[row][col]; if (tileType == 0) { return false; } return true; } The character only moves one tile with this code: If I reduce the col value by two it two more tiles. I think the problem will be around indexing, but I'm totally confused because the zero in the coordinate system of libGDX is in the bottom left corner of the screen, and I don't know the tiles array's indexing is similair or not. The size of the map is 19x21 tiles and looks like the following (the starting position of the player is marked with blue:

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  • Problem with SAT collision detection overlap checking code

    - by handyface
    I'm trying to implement a script that detects whether two rotated rectangles collide for my game, using SAT (Separating Axis Theorem). I used the method explained in the following article for my implementation in Google Dart. 2D Rotated Rectangle Collision I tried to implement this code into my game. Basically from what I understood was that I have two rectangles, these two rectangles can produce four axis (two per rectangle) by subtracting adjacent corner coordinates. Then all the corners from both rectangles need to be projected onto each axis, then multiplying the coordinates of the projection by the axis coordinates (point.x*axis.x+point.y*axis.y) to make a scalar value and checking whether the range of both the rectangle's projections overlap. When all the axis have overlapping projections, there's a collision. First of all, I'm wondering whether my comprehension about this algorithm is correct. If so I'd like to get some pointers in where my implementation (written in Dart, which is very readable for people comfortable with C-syntax) goes wrong. Thanks! EDIT: The question has been solved. For those interested in the working implementation: Click here

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  • Trouble with collision detection in XNA?

    - by Lewis Wilcock
    I'm trying to loop through an list of enemies (enemyList) and then any that have intersected the rectangle belonging to the box object (Which doesn't move), declare there IsAlive bool as false. Then another part of the code removes any enemies that have the IsAlive bool as false. The problem im having is getting access to the variable that holds the Rectangle (named boundingBox) of the enemy. When this is in a foreach loop it works fine, as the enemy class is declared within the foreach. However, there are issues in using the foreach as it removes more than one of the enemies at once (Usually at positions 0 and 2, 1 and 3, etc...). I was wondering the best way to declare the enemy class, without it actually creating new instances of the class? Heres the code I currently have: if (keyboardState.IsKeyDown(Keys.Q) && oldKeyState.IsKeyUp(Keys.Q)) { enemyList.Add(new enemy(textureList.ElementAt(randText), new Vector2(250, 250), graphics)); } //foreach (enemy enemy in enemyList) //{ for (int i = 0; i < enemyList.Count; i++) { if (***enemy.boundingBox***.Intersects(theDefence.boxRectangle)) { enemyList[i].IsDead = true; i++; } } //} for(int j = enemyList.Count - 1; j >= 0; j--) { if(enemyList[j].IsDead) enemyList.RemoveAt(j); } (The enemy.boundingBox is the variables I can't get access too). This is a complete copy of the code (Zipped) If it helps: https://www.dropbox.com/s/ih52k4e21g98j3k/Collision%20tests.rar I managed to find the issue. Changed enemy.boundingBox to enemyList[i].boundingBox. Collision works now! Thanks for any help!

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  • How can I get penetration depth from Minkowski Portal Refinement / Xenocollide?

    - by Raven Dreamer
    I recently got an implementation of Minkowski Portal Refinement (MPR) successfully detecting collision. Even better, my implementation returns a good estimate (local minimum) direction for the minimum penetration depth. So I took a stab at adjusting the algorithm to return the penetration depth in an arbitrary direction, and was modestly successful - my altered method works splendidly for face-edge collision resolution! What it doesn't currently do, is correctly provide the minimum penetration depth for edge-edge scenarios, such as the case on the right: What I perceive to be happening, is that my current method returns the minimum penetration depth to the nearest vertex - which works fine when the collision is actually occurring on the plane of that vertex, but not when the collision happens along an edge. Is there a way I can alter my method to return the penetration depth to the point of collision, rather than the nearest vertex? Here's the method that's supposed to return the minimum penetration distance along a specific direction: public static Vector3 CalcMinDistance(List<Vector3> shape1, List<Vector3> shape2, Vector3 dir) { //holding variables Vector3 n = Vector3.zero; Vector3 swap = Vector3.zero; // v0 = center of Minkowski sum v0 = Vector3.zero; // Avoid case where centers overlap -- any direction is fine in this case //if (v0 == Vector3.zero) return Vector3.zero; //always pass in a valid direction. // v1 = support in direction of origin n = -dir; //get the differnce of the minkowski sum Vector3 v11 = GetSupport(shape1, -n); Vector3 v12 = GetSupport(shape2, n); v1 = v12 - v11; //if the support point is not in the direction of the origin if (v1.Dot(n) <= 0) { //Debug.Log("Could find no points this direction"); return Vector3.zero; } // v2 - support perpendicular to v1,v0 n = v1.Cross(v0); if (n == Vector3.zero) { //v1 and v0 are parallel, which means //the direction leads directly to an endpoint n = v1 - v0; //shortest distance is just n //Debug.Log("2 point return"); return n; } //get the new support point Vector3 v21 = GetSupport(shape1, -n); Vector3 v22 = GetSupport(shape2, n); v2 = v22 - v21; if (v2.Dot(n) <= 0) { //can't reach the origin in this direction, ergo, no collision //Debug.Log("Could not reach edge?"); return Vector2.zero; } // Determine whether origin is on + or - side of plane (v1,v0,v2) //tests linesegments v0v1 and v0v2 n = (v1 - v0).Cross(v2 - v0); float dist = n.Dot(v0); // If the origin is on the - side of the plane, reverse the direction of the plane if (dist > 0) { //swap the winding order of v1 and v2 swap = v1; v1 = v2; v2 = swap; //swap the winding order of v11 and v12 swap = v12; v12 = v11; v11 = swap; //swap the winding order of v11 and v12 swap = v22; v22 = v21; v21 = swap; //and swap the plane normal n = -n; } /// // Phase One: Identify a portal while (true) { // Obtain the support point in a direction perpendicular to the existing plane // Note: This point is guaranteed to lie off the plane Vector3 v31 = GetSupport(shape1, -n); Vector3 v32 = GetSupport(shape2, n); v3 = v32 - v31; if (v3.Dot(n) <= 0) { //can't enclose the origin within our tetrahedron //Debug.Log("Could not reach edge after portal?"); return Vector3.zero; } // If origin is outside (v1,v0,v3), then eliminate v2 and loop if (v1.Cross(v3).Dot(v0) < 0) { //failed to enclose the origin, adjust points; v2 = v3; v21 = v31; v22 = v32; n = (v1 - v0).Cross(v3 - v0); continue; } // If origin is outside (v3,v0,v2), then eliminate v1 and loop if (v3.Cross(v2).Dot(v0) < 0) { //failed to enclose the origin, adjust points; v1 = v3; v11 = v31; v12 = v32; n = (v3 - v0).Cross(v2 - v0); continue; } bool hit = false; /// // Phase Two: Refine the portal int phase2 = 0; // We are now inside of a wedge... while (phase2 < 20) { phase2++; // Compute normal of the wedge face n = (v2 - v1).Cross(v3 - v1); n.Normalize(); // Compute distance from origin to wedge face float d = n.Dot(v1); // If the origin is inside the wedge, we have a hit if (d > 0 ) { //Debug.Log("Do plane test here"); float T = n.Dot(v2) / n.Dot(dir); Vector3 pointInPlane = (dir * T); return pointInPlane; } // Find the support point in the direction of the wedge face Vector3 v41 = GetSupport(shape1, -n); Vector3 v42 = GetSupport(shape2, n); v4 = v42 - v41; float delta = (v4 - v3).Dot(n); float separation = -(v4.Dot(n)); if (delta <= kCollideEpsilon || separation >= 0) { //Debug.Log("Non-convergance detected"); //Debug.Log("Do plane test here"); return Vector3.zero; } // Compute the tetrahedron dividing face (v4,v0,v1) float d1 = v4.Cross(v1).Dot(v0); // Compute the tetrahedron dividing face (v4,v0,v2) float d2 = v4.Cross(v2).Dot(v0); // Compute the tetrahedron dividing face (v4,v0,v3) float d3 = v4.Cross(v3).Dot(v0); if (d1 < 0) { if (d2 < 0) { // Inside d1 & inside d2 ==> eliminate v1 v1 = v4; v11 = v41; v12 = v42; } else { // Inside d1 & outside d2 ==> eliminate v3 v3 = v4; v31 = v41; v32 = v42; } } else { if (d3 < 0) { // Outside d1 & inside d3 ==> eliminate v2 v2 = v4; v21 = v41; v22 = v42; } else { // Outside d1 & outside d3 ==> eliminate v1 v1 = v4; v11 = v41; v12 = v42; } } } return Vector3.zero; } }

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  • Trying to detect collision between two polygons using Separating Axis Theorem

    - by Holly
    The only collision experience i've had was with simple rectangles, i wanted to find something that would allow me to define polygonal areas for collision and have been trying to make sense of SAT using these two links Though i'm a bit iffy with the math for the most part i feel like i understand the theory! Except my implementation somewhere down the line must be off as: (excuse the hideous font) As mentioned above i have defined a CollisionPolygon class where most of my theory is implemented and then have a helper class called Vect which was meant to be for Vectors but has also been used to contain a vertex given that both just have two float values. I've tried stepping through the function and inspecting the values to solve things but given so many axes and vectors and new math to work out as i go i'm struggling to find the erroneous calculation(s) and would really appreciate any help. Apologies if this is not suitable as a question! CollisionPolygon.java: package biz.hireholly.gameplay; import android.graphics.Canvas; import android.graphics.Color; import android.graphics.Paint; import biz.hireholly.gameplay.Types.Vect; public class CollisionPolygon { Paint paint; private Vect[] vertices; private Vect[] separationAxes; CollisionPolygon(Vect[] vertices){ this.vertices = vertices; //compute edges and separations axes separationAxes = new Vect[vertices.length]; for (int i = 0; i < vertices.length; i++) { // get the current vertex Vect p1 = vertices[i]; // get the next vertex Vect p2 = vertices[i + 1 == vertices.length ? 0 : i + 1]; // subtract the two to get the edge vector Vect edge = p1.subtract(p2); // get either perpendicular vector Vect normal = edge.perp(); // the perp method is just (x, y) => (-y, x) or (y, -x) separationAxes[i] = normal; } paint = new Paint(); paint.setColor(Color.RED); } public void draw(Canvas c, int xPos, int yPos){ for (int i = 0; i < vertices.length; i++) { Vect v1 = vertices[i]; Vect v2 = vertices[i + 1 == vertices.length ? 0 : i + 1]; c.drawLine( xPos + v1.x, yPos + v1.y, xPos + v2.x, yPos + v2.y, paint); } } /* consider changing to a static function */ public boolean intersects(CollisionPolygon p){ // loop over this polygons separation exes for (Vect axis : separationAxes) { // project both shapes onto the axis Vect p1 = this.minMaxProjection(axis); Vect p2 = p.minMaxProjection(axis); // do the projections overlap? if (!p1.overlap(p2)) { // then we can guarantee that the shapes do not overlap return false; } } // loop over the other polygons separation axes Vect[] sepAxesOther = p.getSeparationAxes(); for (Vect axis : sepAxesOther) { // project both shapes onto the axis Vect p1 = this.minMaxProjection(axis); Vect p2 = p.minMaxProjection(axis); // do the projections overlap? if (!p1.overlap(p2)) { // then we can guarantee that the shapes do not overlap return false; } } // if we get here then we know that every axis had overlap on it // so we can guarantee an intersection return true; } /* Note projections wont actually be acurate if the axes aren't normalised * but that's not necessary since we just need a boolean return from our * intersects not a Minimum Translation Vector. */ private Vect minMaxProjection(Vect axis) { float min = axis.dot(vertices[0]); float max = min; for (int i = 1; i < vertices.length; i++) { float p = axis.dot(vertices[i]); if (p < min) { min = p; } else if (p > max) { max = p; } } Vect minMaxProj = new Vect(min, max); return minMaxProj; } public Vect[] getSeparationAxes() { return separationAxes; } public Vect[] getVertices() { return vertices; } } Vect.java: package biz.hireholly.gameplay.Types; /* NOTE: Can also be used to hold vertices! Projections, coordinates ect */ public class Vect{ public float x; public float y; public Vect(float x, float y){ this.x = x; this.y = y; } public Vect perp() { return new Vect(-y, x); } public Vect subtract(Vect other) { return new Vect(x - other.x, y - other.y); } public boolean overlap(Vect other) { if( other.x <= y || other.y >= x){ return true; } return false; } /* used specifically for my SAT implementation which i'm figuring out as i go, * references for later.. * http://www.gamedev.net/page/resources/_/technical/game-programming/2d-rotated-rectangle-collision-r2604 * http://www.codezealot.org/archives/55 */ public float scalarDotProjection(Vect other) { //multiplier = dot product / length^2 float multiplier = dot(other) / (x*x + y*y); //to get the x/y of the projection vector multiply by x/y of axis float projX = multiplier * x; float projY = multiplier * y; //we want to return the dot product of the projection, it's meaningless but useful in our SAT case return dot(new Vect(projX,projY)); } public float dot(Vect other){ return (other.x*x + other.y*y); } }

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  • Collision Error

    - by Manji
    I am having trouble with collision detection part of the game. I am using touch events to fire the gun as you will see in the video. Note, the android icon is a temporary graphic for the bullets When ever the user touches (represented by clicks in the video)the bullet appears and kills random sprites. As you can see it never touches the sprites it kills or kill the sprites it does touch. My Question is How do I fix it, so that the sprite dies when the bullet hits it? Collision Code snippet: //Handles Collision private void CheckCollisions(){ synchronized(mSurfaceHolder){ for (int i = sprites.size() - 1; i >= 0; i--){ Sprite sprite = sprites.get(i); if(sprite.isCollision(bullet)){ sprites.remove(sprite); mScore++; if(sprites.size() == 0){ mLevel = mLevel +1; currentLevel++; initLevel(); } break; } } } } Sprite Class Code Snippet: //bounding box left<right and top>bottom int left ; int right ; int top ; int bottom ; public boolean isCollision(Beam other) { // TODO Auto-generated method stub if(this.left>other.right || other.left<other.right)return false; if(this.bottom>other.top || other.bottom<other.top)return false; return true; } EDIT 1: Sprite Class: public class Sprite { // direction = 0 up, 1 left, 2 down, 3 right, // animation = 3 back, 1 left, 0 front, 2 right int[] DIRECTION_TO_ANIMATION_MAP = { 3, 1, 0, 2 }; private static final int BMP_ROWS = 4; private static final int BMP_COLUMNS = 3; private static final int MAX_SPEED = 5; private HitmanView gameView; private Bitmap bmp; private int x; private int y; private int xSpeed; private int ySpeed; private int currentFrame = 0; private int width; private int height; //bounding box left<right and top>bottom int left ; int right ; int top ; int bottom ; public Sprite(HitmanView gameView, Bitmap bmp) { this.width = bmp.getWidth() / BMP_COLUMNS; this.height = bmp.getHeight() / BMP_ROWS; this.gameView = gameView; this.bmp = bmp; Random rnd = new Random(); x = rnd.nextInt(gameView.getWidth() - width); y = rnd.nextInt(gameView.getHeight() - height); xSpeed = rnd.nextInt(MAX_SPEED * 2) - MAX_SPEED; ySpeed = rnd.nextInt(MAX_SPEED * 2) - MAX_SPEED; } private void update() { if (x >= gameView.getWidth() - width - xSpeed || x + xSpeed <= 0) { xSpeed = -xSpeed; } x = x + xSpeed; if (y >= gameView.getHeight() - height - ySpeed || y + ySpeed <= 0) { ySpeed = -ySpeed; } y = y + ySpeed; currentFrame = ++currentFrame % BMP_COLUMNS; } public void onDraw(Canvas canvas) { update(); int srcX = currentFrame * width; int srcY = getAnimationRow() * height; Rect src = new Rect(srcX, srcY, srcX + width, srcY + height); Rect dst = new Rect(x, y, x + width, y + height); canvas.drawBitmap(bmp, src, dst, null); } private int getAnimationRow() { double dirDouble = (Math.atan2(xSpeed, ySpeed) / (Math.PI / 2) + 2); int direction = (int) Math.round(dirDouble) % BMP_ROWS; return DIRECTION_TO_ANIMATION_MAP[direction]; } public boolean isCollision(float x2, float y2){ return x2 > x && x2 < x + width && y2 > y && y2 < y + height; } public boolean isCollision(Beam other) { // TODO Auto-generated method stub if(this.left>other.right || other.left<other.right)return false; if(this.bottom>other.top || other.bottom<other.top)return false; return true; } } Bullet Class: public class Bullet { int mX; int mY; private Bitmap mBitmap; //bounding box left<right and top>bottom int left ; int right ; int top ; int bottom ; public Bullet (Bitmap mBitmap){ this.mBitmap = mBitmap; } public void draw(Canvas canvas, int mX, int mY) { this.mX = mX; this.mY = mY; canvas.drawBitmap(mBitmap, mX, mY, null); } }

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  • Error in my Separating Axis Theorem collision code

    - by Holly
    The only collision experience i've had was with simple rectangles, i wanted to find something that would allow me to define polygonal areas for collision and have been trying to make sense of SAT using these two links Though i'm a bit iffy with the math for the most part i feel like i understand the theory! Except my implementation somewhere down the line must be off as: (excuse the hideous font) As mentioned above i have defined a CollisionPolygon class where most of my theory is implemented and then have a helper class called Vect which was meant to be for Vectors but has also been used to contain a vertex given that both just have two float values. I've tried stepping through the function and inspecting the values to solve things but given so many axes and vectors and new math to work out as i go i'm struggling to find the erroneous calculation(s) and would really appreciate any help. Apologies if this is not suitable as a question! CollisionPolygon.java: package biz.hireholly.gameplay; import android.graphics.Canvas; import android.graphics.Color; import android.graphics.Paint; import biz.hireholly.gameplay.Types.Vect; public class CollisionPolygon { Paint paint; private Vect[] vertices; private Vect[] separationAxes; int x; int y; CollisionPolygon(Vect[] vertices){ this.vertices = vertices; //compute edges and separations axes separationAxes = new Vect[vertices.length]; for (int i = 0; i < vertices.length; i++) { // get the current vertex Vect p1 = vertices[i]; // get the next vertex Vect p2 = vertices[i + 1 == vertices.length ? 0 : i + 1]; // subtract the two to get the edge vector Vect edge = p1.subtract(p2); // get either perpendicular vector Vect normal = edge.perp(); // the perp method is just (x, y) => (-y, x) or (y, -x) separationAxes[i] = normal; } paint = new Paint(); paint.setColor(Color.RED); } public void draw(Canvas c, int xPos, int yPos){ for (int i = 0; i < vertices.length; i++) { Vect v1 = vertices[i]; Vect v2 = vertices[i + 1 == vertices.length ? 0 : i + 1]; c.drawLine( xPos + v1.x, yPos + v1.y, xPos + v2.x, yPos + v2.y, paint); } } public void update(int xPos, int yPos){ x = xPos; y = yPos; } /* consider changing to a static function */ public boolean intersects(CollisionPolygon p){ // loop over this polygons separation exes for (Vect axis : separationAxes) { // project both shapes onto the axis Vect p1 = this.minMaxProjection(axis); Vect p2 = p.minMaxProjection(axis); // do the projections overlap? if (!p1.overlap(p2)) { // then we can guarantee that the shapes do not overlap return false; } } // loop over the other polygons separation axes Vect[] sepAxesOther = p.getSeparationAxes(); for (Vect axis : sepAxesOther) { // project both shapes onto the axis Vect p1 = this.minMaxProjection(axis); Vect p2 = p.minMaxProjection(axis); // do the projections overlap? if (!p1.overlap(p2)) { // then we can guarantee that the shapes do not overlap return false; } } // if we get here then we know that every axis had overlap on it // so we can guarantee an intersection return true; } /* Note projections wont actually be acurate if the axes aren't normalised * but that's not necessary since we just need a boolean return from our * intersects not a Minimum Translation Vector. */ private Vect minMaxProjection(Vect axis) { float min = axis.dot(new Vect(vertices[0].x+x, vertices[0].y+y)); float max = min; for (int i = 1; i < vertices.length; i++) { float p = axis.dot(new Vect(vertices[i].x+x, vertices[i].y+y)); if (p < min) { min = p; } else if (p > max) { max = p; } } Vect minMaxProj = new Vect(min, max); return minMaxProj; } public Vect[] getSeparationAxes() { return separationAxes; } public Vect[] getVertices() { return vertices; } } Vect.java: package biz.hireholly.gameplay.Types; /* NOTE: Can also be used to hold vertices! Projections, coordinates ect */ public class Vect{ public float x; public float y; public Vect(float x, float y){ this.x = x; this.y = y; } public Vect perp() { return new Vect(-y, x); } public Vect subtract(Vect other) { return new Vect(x - other.x, y - other.y); } public boolean overlap(Vect other) { if(y > other.x && other.y > x){ return true; } return false; } /* used specifically for my SAT implementation which i'm figuring out as i go, * references for later.. * http://www.gamedev.net/page/resources/_/technical/game-programming/2d-rotated-rectangle-collision-r2604 * http://www.codezealot.org/archives/55 */ public float scalarDotProjection(Vect other) { //multiplier = dot product / length^2 float multiplier = dot(other) / (x*x + y*y); //to get the x/y of the projection vector multiply by x/y of axis float projX = multiplier * x; float projY = multiplier * y; //we want to return the dot product of the projection, it's meaningless but useful in our SAT case return dot(new Vect(projX,projY)); } public float dot(Vect other){ return (other.x*x + other.y*y); } }

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  • Collision Detection problems in Voxel Engine (XNA)

    - by Darestium
    I am creating a minecraft like terrain engine in XNA and have had some collision problems for quite some time. I have checked and changed my code based on other peoples collision code and I still have the same problem. It always seems to be off by about a block. for instance, if I walk across a bridge which is one block high I fall through it. Also, if you walk towards a "row" of blocks like this: You are able to stand "inside" the left most one, and you collide with nothing in the right most side (where there is no block and is not visible on this image). Here is all my collision code: private void Move(GameTime gameTime, Vector3 direction) { float speed = playermovespeed * (float)gameTime.ElapsedGameTime.TotalSeconds; Matrix rotationMatrix = Matrix.CreateRotationY(player.Camera.LeftRightRotation); Vector3 rotatedVector = Vector3.Transform(direction, rotationMatrix); rotatedVector.Normalize(); Vector3 testVector = rotatedVector; testVector.Normalize(); Vector3 movePosition = player.position + testVector * speed; Vector3 midBodyPoint = movePosition + new Vector3(0, -0.7f, 0); Vector3 headPosition = movePosition + new Vector3(0, 0.1f, 0); if (!world.GetBlock(movePosition).IsSolid && !world.GetBlock(midBodyPoint).IsSolid && !world.GetBlock(headPosition).IsSolid) { player.position += rotatedVector * speed; } //player.position += rotatedVector * speed; } ... public void UpdatePosition(GameTime gameTime) { player.velocity.Y += playergravity * (float)gameTime.ElapsedGameTime.TotalSeconds; Vector3 footPosition = player.Position + new Vector3(0f, -1.5f, 0f); Vector3 headPosition = player.Position + new Vector3(0f, 0.1f, 0f); // If the block below the player is solid the Y velocity should be zero if (world.GetBlock(footPosition).IsSolid || world.GetBlock(headPosition).IsSolid) { player.velocity.Y = 0; } UpdateJump(gameTime); UpdateCounter(gameTime); ProcessInput(gameTime); player.Position = player.Position + player.velocity * (float)gameTime.ElapsedGameTime.TotalSeconds; velocity = Vector3.Zero; } and the one and only function in the camera class: protected void CalculateView() { Matrix rotationMatrix = Matrix.CreateRotationX(upDownRotation) * Matrix.CreateRotationY(leftRightRotation); lookVector = Vector3.Transform(Vector3.Forward, rotationMatrix); cameraFinalTarget = Position + lookVector; Vector3 cameraRotatedUpVector = Vector3.Transform(Vector3.Up, rotationMatrix); viewMatrix = Matrix.CreateLookAt(Position, cameraFinalTarget, cameraRotatedUpVector); } which is called when the rotation variables are changed: public float LeftRightRotation { get { return leftRightRotation; } set { leftRightRotation = value; CalculateView(); } } public float UpDownRotation { get { return upDownRotation; } set { upDownRotation = value; CalculateView(); } } World class: public Block GetBlock(int x, int y, int z) { if (InBounds(x, y, z)) { Vector3i regionalPosition = GetRegionalPosition(x, y, z); Vector3i region = GetRegionPosition(x, y, z); return regions[region.X, region.Y, region.Z].Blocks[regionalPosition.X, regionalPosition.Y, regionalPosition.Z]; } return new Block(BlockType.none); } public Vector3i GetRegionPosition(int x, int y, int z) { int regionx = x == 0 ? 0 : x / Variables.REGION_SIZE_X; int regiony = y == 0 ? 0 : y / Variables.REGION_SIZE_Y; int regionz = z == 0 ? 0 : z / Variables.REGION_SIZE_Z; return new Vector3i(regionx, regiony, regionz); } public Vector3i GetRegionalPosition(int x, int y, int z) { int regionx = x == 0 ? 0 : x / Variables.REGION_SIZE_X; int X = x % Variables.REGION_SIZE_X; int regiony = y == 0 ? 0 : y / Variables.REGION_SIZE_Y; int Y = y % Variables.REGION_SIZE_Y; int regionz = z == 0 ? 0 : z / Variables.REGION_SIZE_Z; int Z = z % Variables.REGION_SIZE_Z; return new Vector3i(X, Y, Z); } Any ideas how to fix this problem? EDIT 1: Graphic of the problem: EDIT 2 GetBlock, Vector3 version: public Block GetBlock(Vector3 position) { int x = (int)Math.Floor(position.X); int y = (int)Math.Floor(position.Y); int z = (int)Math.Ceiling(position.Z); Block block = GetBlock(x, y, z); return block; } Now, the thing is I tested the theroy that the Z is always "off by one" and by ceiling the value it actually works as intended. Altough it still could be greatly more accurate (when you go down holes you can see through the sides, and I doubt it will work with negitive positions). I also does not feel clean Flooring the X and Y values and just Ceiling the Z. I am surely not doing something correctly still.

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  • jBullet Collision/Physics not working correctly

    - by Kenneth Bray
    Below is the code for one of my objects in the game I am creating (yes although this is a cube, I am not making anything remotely like MineCraft), and my issue is I while the cube will display and is does follow the physics if the cube falls, it does not interact with any other objects in the game. If I was to have multiple cubes in screen at once they all just sit there, or shoot off in all directions never stopping. Anyway, I am new to jBullet, and any help would be appreciated. package Object; import static org.lwjgl.opengl.GL11.GL_QUADS; import static org.lwjgl.opengl.GL11.glBegin; import static org.lwjgl.opengl.GL11.glColor3f; import static org.lwjgl.opengl.GL11.glEnd; import static org.lwjgl.opengl.GL11.glPopMatrix; import static org.lwjgl.opengl.GL11.glPushMatrix; import static org.lwjgl.opengl.GL11.glVertex3f; import javax.vecmath.Matrix4f; import javax.vecmath.Quat4f; import javax.vecmath.Vector3f; import com.bulletphysics.collision.shapes.BoxShape; import com.bulletphysics.collision.shapes.CollisionShape; import com.bulletphysics.dynamics.RigidBody; import com.bulletphysics.dynamics.RigidBodyConstructionInfo; import com.bulletphysics.linearmath.DefaultMotionState; import com.bulletphysics.linearmath.Transform; public class Cube { // Cube size/shape variables private float size; boolean cubeCollidable; boolean cubeDestroyable; // Position variables - currently this defines the center of the cube private float posX; private float posY; private float posZ; // Rotation variables - should be between 0 and 359, might consider letting rotation go higher though I can't think of a purpose currently private float rotX; private float rotY; private float rotZ; //collision shape is a box shape CollisionShape fallShape; // setup the motion state for the ball DefaultMotionState fallMotionState; Vector3f fallInertia = new Vector3f(0, 1, 0); RigidBodyConstructionInfo fallRigidBodyCI; public RigidBody fallRigidBody; int mass = 1; // Constructor public Cube(float pX, float pY, float pZ, float pSize) { posX = pX; posY = pY; posZ = pZ; size = pSize; rotX = 0; rotY = 0; rotZ = 0; // define the physics based on the values passed in fallShape = new BoxShape(new Vector3f(size, size, size)); fallMotionState = new DefaultMotionState(new Transform(new Matrix4f(new Quat4f(0, 0, 0, 1), new Vector3f(0, 50, 0), 1f))); fallRigidBodyCI = new RigidBodyConstructionInfo(mass, fallMotionState, fallShape, fallInertia); fallRigidBody = new RigidBody(fallRigidBodyCI); } public void Update() { Transform trans = new Transform(); fallRigidBody.getMotionState().getWorldTransform(trans); posY = trans.origin.x; posX = trans.origin.y; posZ = trans.origin.z; } public void Draw() { fallShape.calculateLocalInertia(mass, fallInertia); // center point posX, posY, posZ float radius = size / 2; //top glPushMatrix(); glBegin(GL_QUADS); { glColor3f(1.0f,0.0f,0.0f); // red glVertex3f(posX + radius, posY + radius, posZ - radius); glVertex3f(posX - radius, posY + radius, posZ - radius); glVertex3f(posX - radius, posY + radius, posZ + radius); glVertex3f(posX + radius, posY + radius, posZ + radius); } glEnd(); glPopMatrix(); //bottom glPushMatrix(); glBegin(GL_QUADS); { glColor3f(1.0f,1.0f,0.0f); // ?? color glVertex3f(posX + radius, posY - radius, posZ + radius); glVertex3f(posX - radius, posY - radius, posZ + radius); glVertex3f(posX - radius, posY - radius, posZ - radius); glVertex3f(posX + radius, posY - radius, posZ - radius); } glEnd(); glPopMatrix(); //right side glPushMatrix(); glBegin(GL_QUADS); { glColor3f(1.0f,0.0f,1.0f); // ?? color glVertex3f(posX + radius, posY + radius, posZ + radius); glVertex3f(posX + radius, posY - radius, posZ + radius); glVertex3f(posX + radius, posY - radius, posZ - radius); glVertex3f(posX + radius, posY + radius, posZ - radius); } glEnd(); glPopMatrix(); //left side glPushMatrix(); glBegin(GL_QUADS); { glColor3f(0.0f,1.0f,1.0f); // ?? color glVertex3f(posX - radius, posY + radius, posZ - radius); glVertex3f(posX - radius, posY - radius, posZ - radius); glVertex3f(posX - radius, posY - radius, posZ + radius); glVertex3f(posX - radius, posY + radius, posZ + radius); } glEnd(); glPopMatrix(); //front side glPushMatrix(); glBegin(GL_QUADS); { glColor3f(0.0f,0.0f,1.0f); //blue glVertex3f(posX + radius, posY + radius, posZ + radius); glVertex3f(posX - radius, posY + radius, posZ + radius); glVertex3f(posX - radius, posY - radius, posZ + radius); glVertex3f(posX + radius, posY - radius, posZ + radius); } glEnd(); glPopMatrix(); //back side glPushMatrix(); glBegin(GL_QUADS); { glColor3f(0.0f,1.0f,0.0f); // green glVertex3f(posX + radius, posY - radius, posZ - radius); glVertex3f(posX - radius, posY - radius, posZ - radius); glVertex3f(posX - radius, posY + radius, posZ - radius); glVertex3f(posX + radius, posY + radius, posZ - radius); } glEnd(); glPopMatrix(); } }

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  • XNA Per-Polygon Collision Check

    - by user22985
    I'm working on a project in XNA for WP7 with a low-poly environment, my problem is I need to setup a working per-polygon collision check between 2 or more 3d meshes. I've checked tons of tutorials but all of them use bounding-boxes, bounding-spheres,rays etc., but what I really need is a VERY precise way of checking if the polygons of two distinct models have intersected or not. If you could redirect me to an example or at least give me some pointers I would be grateful.

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  • My grid based collision detection is slow

    - by Fibericon
    Something about my implementation of a basic 2x4 grid for collision detection is slow - so slow in fact, that it's actually faster to simply check every bullet from every enemy to see if the BoundingSphere intersects with that of my ship. It becomes noticeably slow when I have approximately 1000 bullets on the screen (36 enemies shooting 3 bullets every .5 seconds). By commenting it out bit by bit, I've determined that the code used to add them to the grid is what's slowest. Here's how I add them to the grid: for (int i = 0; i < enemy[x].gun.NumBullets; i++) { if (enemy[x].gun.bulletList[i].isActive) { enemy[x].gun.bulletList[i].Update(timeDelta); int bulletPosition = 0; if (enemy[x].gun.bulletList[i].position.Y < 0) { bulletPosition = (int)Math.Floor((enemy[x].gun.bulletList[i].position.X + 900) / 450); } else { bulletPosition = (int)Math.Floor((enemy[x].gun.bulletList[i].position.X + 900) / 450) + 4; } GridItem bulletItem = new GridItem(); bulletItem.index = i; bulletItem.type = 5; bulletItem.parentIndex = x; if (bulletPosition > -1 && bulletPosition < 8) { if (!grid[bulletPosition].Contains(bulletItem)) { for (int j = 0; j < grid.Length; j++) { grid[j].Remove(bulletItem); } grid[bulletPosition].Add(bulletItem); } } } } And here's how I check if it collides with the ship: if (ship.isActive && !ship.invincible) { BoundingSphere shipSphere = new BoundingSphere( ship.Position, ship.Model.Meshes[0].BoundingSphere.Radius * 9.0f); for (int i = 0; i < grid.Length; i++) { if (grid[i].Contains(shipItem)) { for (int j = 0; j < grid[i].Count; j++) { //Other collision types omitted else if (grid[i][j].type == 5) { if (enemy[grid[i][j].parentIndex].gun.bulletList[grid[i][j].index].isActive) { BoundingSphere bulletSphere = new BoundingSphere(enemy[grid[i][j].parentIndex].gun.bulletList[grid[i][j].index].position, enemy[grid[i][j].parentIndex].gun.bulletModel.Meshes[0].BoundingSphere.Radius); if (shipSphere.Intersects(bulletSphere)) { ship.health -= enemy[grid[i][j].parentIndex].gun.damage; enemy[grid[i][j].parentIndex].gun.bulletList[grid[i][j].index].isActive = false; grid[i].RemoveAt(j); break; //no need to check other bullets } } else { grid[i].RemoveAt(j); } } What am I doing wrong here? I thought a grid implementation would be faster than checking each one.

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  • 2D SAT Collision Detection not working when using certain polygons

    - by sFuller
    My SAT algorithm falsely reports that collision is occurring when using certain polygons. I believe this happens when using a polygon that does not contain a right angle. Here is a simple diagram of what is going wrong: Here is the problematic code: std::vector<vec2> axesB = polygonB->GetAxes(); //loop over axes B for(int i = 0; i < axesB.size(); i++) { float minA,minB,maxA,maxB; polygonA->Project(axesB[i],&minA,&maxA); polygonB->Project(axesB[i],&minB,&maxB); float intervalDistance = polygonA->GetIntervalDistance(minA, maxA, minB, maxB); if(intervalDistance >= 0) return false; //Collision not occurring } This function retrieves axes from the polygon: std::vector<vec2> Polygon::GetAxes() { std::vector<vec2> axes; for(int i = 0; i < verts.size(); i++) { vec2 a = verts[i]; vec2 b = verts[(i+1)%verts.size()]; vec2 edge = b-a; axes.push_back(vec2(-edge.y,edge.x).GetNormailzed()); } return axes; } This function returns the normalized vector: vec2 vec2::GetNormailzed() { float mag = sqrt( x*x + y*y ); return *this/mag; } This function projects a polygon onto an axis: void Polygon::Project(vec2* axis, float* min, float* max) { float d = axis->DotProduct(&verts[0]); float _min = d; float _max = d; for(int i = 1; i < verts.size(); i++) { d = axis->DotProduct(&verts[i]); _min = std::min(_min,d); _max = std::max(_max,d); } *min = _min; *max = _max; } This function returns the dot product of the vector with another vector. float vec2::DotProduct(vec2* other) { return (x*other->x + y*other->y); } Could anyone give me a pointer in the right direction to what could be causing this bug?

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  • 2D SAT Collision Detection not working when using certain polygons (With example)

    - by sFuller
    My SAT algorithm falsely reports that collision is occurring when using certain polygons. I believe this happens when using a polygon that does not contain a right angle. Here is a simple diagram of what is going wrong: Here is the problematic code: std::vector<vec2> axesB = polygonB->GetAxes(); //loop over axes B for(int i = 0; i < axesB.size(); i++) { float minA,minB,maxA,maxB; polygonA->Project(axesB[i],&minA,&maxA); polygonB->Project(axesB[i],&minB,&maxB); float intervalDistance = polygonA->GetIntervalDistance(minA, maxA, minB, maxB); if(intervalDistance >= 0) return false; //Collision not occurring } This function retrieves axes from the polygon: std::vector<vec2> Polygon::GetAxes() { std::vector<vec2> axes; for(int i = 0; i < verts.size(); i++) { vec2 a = verts[i]; vec2 b = verts[(i+1)%verts.size()]; vec2 edge = b-a; axes.push_back(vec2(-edge.y,edge.x).GetNormailzed()); } return axes; } This function returns the normalized vector: vec2 vec2::GetNormailzed() { float mag = sqrt( x*x + y*y ); return *this/mag; } This function projects a polygon onto an axis: void Polygon::Project(vec2* axis, float* min, float* max) { float d = axis->DotProduct(&verts[0]); float _min = d; float _max = d; for(int i = 1; i < verts.size(); i++) { d = axis->DotProduct(&verts[i]); _min = std::min(_min,d); _max = std::max(_max,d); } *min = _min; *max = _max; } This function returns the dot product of the vector with another vector. float vec2::DotProduct(vec2* other) { return (x*other->x + y*other->y); } Could anyone give me a pointer in the right direction to what could be causing this bug? Edit: I forgot this function, which gives me the interval distance: float Polygon::GetIntervalDistance(float minA, float maxA, float minB, float maxB) { float intervalDistance; if (minA < minB) { intervalDistance = minB - maxA; } else { intervalDistance = minA - maxB; } return intervalDistance; //A positive value indicates this axis can be separated. } Edit 2: I have recreated the problem in HTML5/Javascript: Demo

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