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  • Sprites rendering blurry with velocity

    - by ashes999
    After adding velocity to my game, I feel like my textures are twitching. I thought it was just my eyes, until I finally captured it in a screenshot: The one on the left is what renders in my game; the one on the right is the original sprite, pasted over. (This is a screenshot from Photoshop, zoomed in 6x.) Notice the edges are aliasing -- it looks almost like sub-pixel rendering. In fact, if I had not forced my sprites (which have position and velocity as ints) to draw using integer values, I would swear that MonoGame is drawing with floating point values. But it isn't. What could be the cause of these things appearing blurry? It doesn't happen without velocity applied. To be precise, my SpriteComponent class has a Vector2 Position field. When I call Draw, I essentially use new Vector2((int)Math.Round(this.Position.X), (int)Math.Round(this.Position.Y)) for the position. I had a bug before where even stationary objects would jitter -- that was due to me using the straight Position vector and not rounding the values to ints. If I use Floor/Ceiling instead of round, the sprite sinks/hovers (one pixel difference either way) but still draws blurry.

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  • Can't remove JPanel from JFrame while adding new class into it

    - by A.K.
    Basically, I have my Frame class, which instantiates all the properties for the JFrame, and draws a JLabel with an image (my title screen). Then I made a separate JPanel with a start button on it, and made a mouse listener that will allow me to remove these objects while adding in a new Board() class (Which paints the main game). *Note: The JLabel is SEPARATE from the JPanel, but it still gets moved to the side by it. Problem: Whenever I click the button though, it only shows a little square of what I presume is my board class trying to run. Code below for the Frame Class: package OurPackage; //Made By A.K. 5/24/12 //Contains Frame. import java.awt.BorderLayout; import java.awt.Color; import java.awt.Container; import java.awt.Dimension; import java.awt.Graphics; import java.awt.Graphics2D; import java.awt.GridBagLayout; import java.awt.GridLayout; import java.awt.Image; import java.awt.Rectangle; import java.awt.event.ActionEvent; import java.awt.event.ActionListener; import java.awt.event.KeyEvent; import java.awt.event.MouseAdapter; import java.awt.event.MouseEvent; import java.awt.event.MouseListener; import javax.swing.*; import javax.swing.plaf.basic.BasicOptionPaneUI.ButtonActionListener; public class Frame implements MouseListener { public static boolean StartGame = false; ImageIcon img = new ImageIcon(getClass().getResource("/Images/ActionJackTitle.png")); ImageIcon StartImg = new ImageIcon(getClass().getResource("/Images/JackStart.png")); public Image Title; JLabel TitleL = new JLabel(img); public JPanel panel = new JPanel(); JButton StartB = new JButton(StartImg); JFrame frm = new JFrame("Action-Packed Jack"); public Frame() { TitleL.setPreferredSize(new Dimension(1200, 420)); frm.add(TitleL); frm.setLayout(new GridBagLayout()); frm.add(panel); panel.setSize(new Dimension(220, 45)); panel.setLayout(new GridBagLayout ()); panel.add(StartB); StartB.addMouseListener(this); StartB.setPreferredSize(new Dimension(220, 45)); frm.setDefaultCloseOperation(JFrame.EXIT_ON_CLOSE); frm.setSize(1200, 420); frm.setVisible(true); frm.setResizable(false); frm.setLocationRelativeTo(null); } public static void main(String[] args) { new Frame(); } public void mouseClicked(MouseEvent e) { StartB.setContentAreaFilled(false); panel.remove(StartB); frm.remove(panel); frm.remove(TitleL); //frm.setLayout(null); frm.add(new Board()); //Add Game "Tiles" Or Content. x = 1200 frm.validate(); System.out.println("Hit!"); } @Override public void mouseEntered(MouseEvent arg0) { // TODO Auto-generated method stub } @Override public void mouseExited(MouseEvent arg0) { // TODO Auto-generated method stub } @Override public void mousePressed(MouseEvent arg0) { // TODO Auto-generated method stub } @Override public void mouseReleased(MouseEvent arg0) { // TODO Auto-generated method stub } }

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  • Queries regarding Geometry Shaders

    - by maverick9888
    I am dealing with geometry shaders using GL_ARB_geometry_shader4 extension. My code goes like : GLfloat vertices[] = { 0.5,0.25,1.0, 0.5,0.75,1.0, -0.5,0.75,1.0, -0.5,0.25,1.0, 0.6,0.35,1.0, 0.6,0.85,1.0, -0.6,0.85,1.0, -0.6,0.35,1.0 }; glProgramParameteriEXT(psId, GL_GEOMETRY_INPUT_TYPE_EXT, GL_TRIANGLES); glProgramParameteriEXT(psId, GL_GEOMETRY_OUTPUT_TYPE_EXT, GL_TRIANGLE_STRIP); glLinkProgram(psId); glBindAttribLocation(psId,0,"Position"); glEnableVertexAttribArray (0); glVertexAttribPointer(0, 3, GL_FLOAT, 0, 0, vertices); glDrawArrays(GL_TRIANGLE_STRIP,0,4); My vertex shader is : #version 150 in vec3 Position; void main() { gl_Position = vec4(Position,1.0); } Geometry shader is : #version 150 #extension GL_EXT_geometry_shader4 : enable in vec4 pos[3]; void main() { int i; vec4 vertex; gl_Position = pos[0]; EmitVertex(); gl_Position = pos[1]; EmitVertex(); gl_Position = pos[2]; EmitVertex(); gl_Position = pos[0] + vec4(0.3,0.0,0.0,0.0); EmitVertex(); EndPrimitive(); } Nothing is rendered with this code. What exactly should be the mode in glDrawArrays() ? How does the GL_GEOMETRY_OUTPUT_TYPE_EXT parameter will affect glDrawArrays() ? What I expect is 3 vertices will be passed on to Geometry Shader and using those we construct a primitive of size 4 (assuming GL_TRIANGLE_STRIP requires 4 vertices). Can somebody please throw some light on this ?

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  • Automatically zoom out the camera to show all players

    - by user36159
    I am building a game in XNA that takes place in a rectangular arena. The game is multiplayer and each player may go where they like within the arena. The camera is a perspective camera that looks directly downwards. The camera should be automatically repositioned based on the game state. Currently, the xy position is a weighted sum of the xy positions of important entities. I would like the camera's z position to be calculated from the xy coordinates so that it zooms out to the point where all important entities are visible. My current approach is to: hw = the greatest x distance from the camera to an important entity hh = the greatest y distance from the camera to an important entity Calculate z = max(hw / tan(FoVx), hh / tan(FoVy)) My code seems to almost work as it should, but the resulting z values are always too low by a factor of about 4. Any ideas?

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  • Customize Colors for Sprites in Web Game

    - by NateDSaint
    So I'm working on an html5/javascript/css3-based game. Without going into too much detail, I'm thinking of having the characters be simple 8 or 16-bit style sprites, but I'd like to allow the user to customize the colors of their character. Here are some examples of what I'm talking about : http://jsfiddle.net/simurai/CGmCe/light/ http://www.splashnology.com/article/sprite-animation-in-css3/1485/ So the problem I'm having is two-fold: 1) Should I use something other than a sprite map for my characters, like actually draw them as shapes and animate them in a canvas element? That way I can fill the sprite with colors of the user's choosing? My fear there is that this would be inefficient as far as resources and also waste a lot of time hand-drawing everything, but could allow other customization (like height/width etc). 2) Are there potentially some web apis that would allow you to alter colors inside of a sprite? I suppose I could do it on the back-end with GD, but I'm trying to make it entirely in-browser (including local storage). It's not a definitive one-answer only question, but I'm hoping someone can suggest something they've seen that approaches the same problem from another angle or gives us a way to customize the sprites or manipulate them in some manner. Or avoid them altogether, and use a different method.

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  • What's the difference between Canvas and WebGL?

    - by gadr90
    I'm thinking about using CAAT as a part of a HTML5 game engine. One of it's features is the ability to render to Canvas and WebGL without changing anything in the client code. That is a good thing, but I haven't found precisely: what are the differences between those two technologies? I would specially like to know the differences of Canvas and WebGL in the following regards: Framerate Desktop browser support Mobile browser support Futureproofability (TM)

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  • Play audio in javascript with a good performance

    - by João
    I'm developing a browser game where the player can shoot. Everytime he shoots it play a sound. Currently i'm using this code to play sounds in JavaScript: var audio = document.createElement("audio"); audio.src = "my_sound.mp3"; audio.play(); I'm worried about performance here. Will 10 simultaneous sounds impact my game performance too much? Will all audio objects stay in memory even after they are played?

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  • Textures of .x model deformed in XNA

    - by marc wellman
    I want to have a 3D model with textures built in SketchUp 8 be imported as a .x model in XNA. So far I have used several .x exporters like http://edecadoudal.googlepages.com/xExporter.rb 3D RAD zbylsxexporter With all of them I have the same problem: The model gets built correctly but the textures are deformed. The sizes of my texture files are multiples of four and inside Sketchup the model looks prefect. That's the texture file which is 256x256: And this is how it looks like in my XNA program: What can I do?

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  • Moving a body in a specific direction using XNA with Farseer Physics

    - by Code Assasssin
    I have a custom polygon attached to a body, which looks like this: What I am trying to accomplish is getting the body to move according to wherever the tip of the body is. So far this is what I've tried: if (ks.IsKeyDown(Keys.Up)) { body.ApplyForce(new Vector2(0, -20),body.GetLocalPoint(new Vector2(0,0))); } if (ks.IsKeyDown(Keys.Left)) { body.ApplyTorque(-500); } if (ks.IsKeyDown(Keys.Right)) { body.ApplyTorque(500); } The body rotates fine - but when I try making the body accelerate according to the tip of the body - assuming I have specified the tip correctly(I am pretty sure I haven't), it just spins around, as if I have applied Torque to it. Can anyone point me in the right direction of how to fix this problem?

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  • Regulating how much to draw based on how much was drawn last frame.

    - by Mike Howard
    I have a 3D game world on an iPhone (limited graphics speed), and I'm already regulating whether I draw each shape on the screen based on it's size and distance from the camera. Something like... if (how_big_it_looks_from_the_camera > constant) then draw What I want to do now is also take into account how many shapes are being drawn, so that in busier areas of the game world I can draw less than I otherwise would. I tried to do this by dividing how_big_it_looks by the number of shapes that were drawn last frame (well, the square root of this but I'm simplifying - the problem is the same). if (how_big_it_looks / shapes_drawn > constant2) then draw But the check happens at the level of objects which represent many drawn shapes, and if an object containing many shapes is switched on, it increases shapes_drawn lots and switches itself back off the next frame. It flickers on and off. I tried keeping a kind of weighted average of previous values, by each frame doing something like shapes_drawn_recently = 0.9 * shapes_drawn_recently + 0.1 * shapes_just_drawn, but of course it only slows the flickering down because of the nature of the feedback loop. Is there a good way of solving this? My project is in Objective-C, but a general algorithm or pseudo-code is good too. Thanks.

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  • OpenGL ES 2 on Android: native window

    - by ThreaderSlash
    According to OGLES specification, we have the following definition: EGLSurface eglCreateWindowSurface(EGLDisplay display, EGLConfig config, NativeWindowType native_window, EGLint const * attrib_list) More details, here: http://www.khronos.org/opengles/documentation/opengles1_0/html/eglCreateWindowSurface.html And also by definition: int32_t ANativeWindow_setBuffersGeometry(ANativeWindow* window, int32_t width, int32_t height, int32_t format); More details, here: http://mobilepearls.com/labs/native-android-api I am running Android Native App on OGLES 2 and debugging it in a Samsung Nexus device. For setting up the 3D scene graph environment, the following variables are defined: struct android_app { ... ANativeWindow* window; }; android_app* mApplication; ... mApplication=&pApplication; And to initialize the App, we run the commands in the code: ANativeWindow_setBuffersGeometry(mApplication->window, 0, 0, lFormat); mSurface = eglCreateWindowSurface(mDisplay, lConfig, mApplication->window, NULL); Funny to say is that, the command ANativeWindow_setBuffersGeometry behaves as expected and works fine according to its definition, accepting all the parameters sent to it. But the eglCreateWindowSurface does no accept the parameter mApplication-window, as it should accept according to its definition. Instead, it looks for the following input: EGLNativeWindowType hWnd; mSurface = eglCreateWindowSurface(mDisplay,lConfig,hWnd,NULL); As an alternative, I considered to use instead: NativeWindowType hWnd=android_createDisplaySurface(); But debugger says: Function 'android_createDisplaySurface' could not be resolved Is 'android_createDisplaySurface' compatible only for OGLES 1 and not for OGLES 2? Can someone tell if there is a way to convert mApplication-window? In a way that the data from the android_app get accepted to the window surface?

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  • How to teach game programming at school ?

    - by jokoon
    I'm in this private school right now, and apart from my progressive stoppage of anti-depressants, I'm having an hard time focusing on what the school wants me to do. The school has a professional contract for a game we have to do with Unity. I don't really learn anything new while using unity, so I don't like using it. We recently learned how to use DirectX, and we have to do some sort of Gradius-precursor clone (Parsec) with directX, in 3D: this annoys me, and I'm currently learning to use Ogre3D by myself by making some game. The teacher is an engineer, and all of us won't be engineers. How would you teach game programming ?

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  • How does Starcraft 2 load it's metadata?

    - by chobok
    Lets say you are playing Starcraft 2 melee map. The game loads the map. Melee maps have the following dependencies: Liberty (Mod) Liberty Multi (Mod) I think the game engine will load the data from Liberty (Mod) first, then from Liberty Multi (Mod). For data that exists in both dependencies, the engine will use the one from Liberty Multi (Mod). Is this correct? Liberty Multi (Mod) is updated with each patch of Starcraft 2. Does the game engine load just the latest version of Liberty Multi (Mod)? or Does the game engine load all the versions and overwrite duplicate data with the latest version?

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  • 3D Vector "End Point" Calculation for procedural Vector Graphics

    - by FrostFlame64
    Alright, So I need some help with some Vector Math. I've developing some game Engines that have Procedural Fractal Generation for Some Graphics, such as using Lindenmayer Systems for generating Trees and Plants. L-Systems, are drawn by using Turtle Graphics, which is a form of Vector graphics. I first created a system to draw in 2D Graphics, which works perfectly fine. But now I want to make a 3D equivalent, and I’ve run into an issue. For my 2D Version, I created a Method for quickly determining the “End Point” of a Vector-like movement. Given a starting point (X, Y), a direction (between 0 and 360 degrees), and a distance, the end point is calculated by these formulas: newX = startX + distance * Sin((PI * direction) / 180) newY = startY + distance * Cos((PI * direction) / 180) Now I need something Similarly Equivalent for performing this Calculation in 3D, But I haven’t been able to Google anything that could show me how to do this. I'm flexible enough to get whatever required information is needed for this method calculation, in any reasonable form (Vector3, Quaternion, ect). To summarize: Given a starting point/vector position in 3D space (X, Y, Z), a Direction in 3D space (Vector3, Quaternion, ect), and a Distance, I need to find the “End Point” in 3D Space. Thank you for your time and help.

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  • How to highlight non-rectangular hotspots?

    - by HuseyinUslu
    So my question is highly related to Creating non-rectangular hotspots and detecting clicks. Yet again, I've irregular hot-spots (think the game Risk). So basically, we can detect clicks on these hot-spots easily using color key mapping as discussed in above question which I don't have any problems implementing (which is also covered here in details). The problem is about highlighting these irreguar hotspots. So let me explain the question a bit more - the above color key mapping guide uses this as a world map: Then the author color-maps the imaginary countries: Now we can now detect the country the pointer is over. In the same article author mentions outlining countries on mouse-over. Though to get the effect, he creates unique border assets for each country - like: For the game I'm working on I'm using the same color-key mapping idea to detect hot-spots, but I didn't like the way of highlighting hot-spots. Coloring all the hot-spots is already a time-consuming job for me - as I have 25+ hot-spots for each map. Further, the need to have 25 unique border/highlight asset per hot-spot doesn't sound right. Anyone have a better idea/suggestion on highlighting these hot-spots?

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  • how can i move static box2d object.

    - by user5198
    how can i move static box2d sprites. i have tried this tutorial from . http://www.raywenderlich.com/475/how-to-create-a-simple-breakout-game-with-box2d-and-cocos2d-tutorial-part-12. I managed to add another "paddle" object with box2d body, but i can seam to be able to make the code to move the second "paddle" body. Can anyone direct me how to do it? Is there a way to move a "b2_staticBody" box 2d object? i have tried, but i can only move it when i use "b2_dynamicBody" if i used "b2_staticBody" i can move it at all.

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  • Absorbtion 2d image effect

    - by Ed.
    I want to create a specyfic 2d image effect. It consists in modifying a sprite so it looks like it is being zoomed to a point or "absorbed" by that point. I'm not really sure what is the technical name of this effect so I cannot explain it correctly. Here you can see a video of what I'm talking about, it is the effect when the character absorbs the three glyphs. http://www.youtube.com/watch?v=PIo-GddsMcU&t=4m45s What is the name of this effect? How can I implement it with XNA for 2D textures/sprites?

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  • Dynamic Terrain Texture

    - by lgrevenl
    I've been looking at a 2D physics game called 'Hill Climb Racing' (Android and iOS) and was wondering how they went about texturing the terrain? I've had a think about it and I've come up with nothing and finding a resource on the web has proved impossible. Please help. The game mentioned uses Cocos2d. Would it be just as doable in a different environment? EDIT: I was looking at another question: Drawing large 2D sidescroller level terrain The end result is what I'm looking for, but in my mind I was thinking that there would be some way to add this effect (using small textures) to some terrain specified by vertices rather than making a very large image to match whatever is seen in the level.

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  • How to have operations with character/items in binary with concrete operations?

    - by Piperoman
    I have the next problem. A item can have a lot of states: NORMAL = 0000000 DRY = 0000001 HOT = 0000010 BURNING = 0000100 WET = 0001000 COLD = 0010000 FROZEN = 0100000 POISONED= 1000000 A item can have some states at same time but not all of them Is impossible to be dry and wet at same time. If you COLD a WET item, it turns into FROZEN. If you HOT a WET item, it turns into NORMAL A item can be BURNING and POISON Etc. I have tried to set binary flags to states, and use AND to combine different states, checking before if it is possible or not to do it, or change to another status. Does there exist a concrete approach to solve this problem efficiently without having an interminable switch that checks every state with every new state? It is relatively easy to check 2 different states, but if there exists a third state it is not trivial to do.

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  • In-Game Encyclopedias

    - by SHiNKiROU
    There are some games where there is an in-game encyclopedia where you can know many things about characters and settings of the game. For example, the Codex in Mass Effect. I want to know if it is exclusive to Bioware, and get inspired about other encyclopedia systems. What are some other examples of in-game encyclopedias? How effective is it? I also want some examples where the in-game encyclopedia is not effective at all or an ignored feature

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  • Math major as a viable degree

    - by Zak O'Keefe
    While I realize there are many topics about CS vs software engineering vs game school programs, I haven't found anything relating to whether pure math degrees (with CS minor and electives) would also be a viable program. By this I mean: Would having a math major, CS minor put one at competitive disadvantage as compared to a pure CS program? This relates specifically to game engine programming, more on the graphics side. Background (for those who care): Currently a math major, CS minor at school and looking to land a career doing graphics engine programming. Admittedly, I love math and if at all possible would like to stay my current program as long as it doesn't put me at a competitive disadvantage trying to land a job post-graduation. That being said, I'm strong in the traditional C/C++ languages, strong concurrent programming skills, and currently produce self-made games for iOS. As an employer, how badly is the math major hurting me? Just want to get some advice from people already in the field!

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  • Applying Textures to Hexagonal Tiles Seamlessly

    - by PATRY
    I'm doing a tactical game (X-Com / Fallout style) for fun. I've decided to use a hexagonal map, but I'm having a graphic problem. My current map display is HUD-like, with only the border of the map cells displayed, without any texture. it's simple and allow for display of different types of informations by varying the color of the border. For exemple the "danger view mode" displays the borders with a color going from green (no damage possible) to red (prob of damage 90%). Now, It's a bit hard to differentiate the kind of tile the player is on. I could put a plain color (green is grass, pale blue is water...), but this is going to limit the possibilities. Thus, i would like to display a texture on my tiles. Since the map are generated, i can not use a picture for the whole map with the HUD over. So, my question is : does any one knows how i could generate the sealess hexagonal textures (algo or plugin), or if there is a site with some hexagonal tiles ?

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  • Vertical Scrolling In Tile Based XNA Platformer

    - by alec100_94
    I'm making a 2D platformer in XNA 4.0. I have created a working tile engine, which works well for my purposes, and Horizontal Scrolling works flawlessly, however I am having great trouble with Vertical scrolling. I Basically want the camera to scroll up (world to scroll down) when the player reaches a certain Y co-ordinate, and I would also like to automatically scroll back down if coming down, and that co-ordinate is passed. My biggest problem is I have no real way of detecting the direction the player is moving in using only the Y Co-ord. Here Is My Code Code For The Camera Class (which appears to be a very different approach to most camera classes I have seen). using System; using System.Collections.Generic; using System.Linq; using System.Text; using Microsoft.Xna.Framework; namespace Marvin { class Camera : TileEngine { public static bool startReached; public static bool endReached; public static void MoveRight(float speed = 2) { //Moves The Position of Each Tile Right foreach (Tile t in tiles) { if(t!=null) { t.position.X -= speed; } } } public static void MoveLeft(float speed = 2) { //Moves The Position of Each Tile Right foreach (Tile t in tiles) { if(t!=null) { t.position.X += speed; } } } public static void MoveUp(float speed = 2) { foreach (Tile t in tiles) { if(t!=null) { t.position.Y += speed; } } } public static void MoveDown(float speed = 2) { foreach (Tile t in tiles) { if(t!=null) { t.position.Y -= speed; } } } public static void Restrain() { if(tiles.Last().position.X<Main.graphics.PreferredBackBufferWidth-tiles.Last().size.X) { MoveLeft(); endReached = true; } else { endReached = false; } if(tiles[1].position.X>0) { MoveRight(); startReached = true;} else { startReached = false; } } } } Here is My Player Code for Left and Right Scrolling/Moving if (Main.currentKeyState.IsKeyDown(Keys.Right)) { Camera.MoveRight(); if(Camera.endReached) { MoveRight(2); } else { if(marvin.GetRectangle().X!=Main.graphics.PreferredBackBufferWidth-(marvin.GetRectangle().X+marvin.GetRectangle().Width)) { MoveRight(2); Camera.MoveLeft(); } } } if(Main.currentKeyState.IsKeyDown(Keys.Left)) { Camera.MoveLeft(); if(Camera.startReached) { MoveLeft(2); } else { if(marvin.GetRectangle().X!=Main.graphics.PreferredBackBufferWidth-(marvin.GetRectangle().X+marvin.GetRectangle().Width)) { MoveLeft(2); Camera.MoveRight(); } } } Camera.Restrain(); if(marvin.GetRectangle().X>Main.graphics.PreferredBackBufferWidth-marvin.GetRectangle().Width) { MoveLeft(2); } if(marvin.GetRectangle().X<0) { MoveRight(2); } And Here Is My Player Jumping/Falling Code which may cause some conflicts with the vertical camera movement. if (!jumping) { if(!TileEngine.TopOfTileCollidingWith(footBounds)) { MoveDown(5); } else { if(marvin.GetRectangle().Y != TileEngine.LastPlatformStoodOnTop()-marvin.GetRectangle().Height) { float difference = (TileEngine.LastPlatformStoodOnTop()-marvin.GetRectangle().Height) - (marvin.GetRectangle().Y); marvin.SetRectangle(marvin.GetRectangle().X,(int)(marvin.GetRectangle().Y+difference)); armR.SetRectangle(armR.GetRectangle().X,(int)(armR.GetRectangle().Y+difference)); armL.SetRectangle(armL.GetRectangle().X,(int)(armL.GetRectangle().Y+difference)); eyeL.SetRectangle(eyeL.GetRectangle().X,(int)(eyeL.GetRectangle().Y+difference)); eyeR.SetRectangle(eyeR.GetRectangle().X,(int)(eyeR.GetRectangle().Y+difference)); } } } if (Main.currentKeyState.IsKeyDown(Keys.Up) && Main.previousKeyState.IsKeyUp(Keys.Up) && TileEngine.TopOfTileCollidingWith(footBounds)) { jumping = true; } if(jumping) { if(TileEngine.LastPlatformStoodOnTop()>0 && (TileEngine.LastPlatformStoodOnTop() - footBounds.Bottom)<120) { MoveUp(5); } else { jumping = false; } } All player code I have tried for vertical movements has failed, or caused weird results (like falling through platforms), and most have been a variation on the method I described above, hence I have not included it. I would really appreciate some help implementing a simple vertical scrolling into this game, Thanks.

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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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  • box2d resize bodies arround point

    - by philipp
    I have a compound object, consisting of a b2Body, vector-graphics and a list polygons which describe the b2body's shapes. This object has its own transformation matrix to centralize the storage of transformations. So far everything is working quiet fine, even scaling works, but not if i scale around a point. In the initialization phase of the object it is scaled around a point. This happens in this order: transform the main matrix transform the vector graphics and the polygons recreate the b2Body After this function ran, the shapes and all the graphics are exactly where they should be, BUT: after the first steps of the b2World the graphical stuff moves away from the body. When I ran the debugger I found out that the position of the body is 0/0 the red dot shows the center of scaling. the first image shows the basic setup and the second the final position of the graphics. This distance stays constant for the rest of the simulation. If I set the position via myBody.SetPosition( sx, sy ); the whole scenario just plays a bit more distant for the origin. Any Idea how to fix this? EDIT:: I came deeper down to the problem and it lies in the fact that i must not scale the transform matrix for the b2body shapes around the center, but set the b2body's position back to the point after scaling. But how can I calculate that point? EDIT 2 :: I came ever deeper down to it, even solved it, but this is a slow solution and i hope that there is somebody who understands what formula I need. assuming to have a set polygons relative to an origin as basis shapes for a b2body: scaling the whole object around a certain point is done in the following steps: i scale everything around the center except the polygons i create a clone of the polygons matrix i scale this clone around the point i calculate dx, dy as difference of clone.tx - original.tx and clone.ty - original.ty i scale the original polygon matrix NOT around the point i recreate the body i create the fixture i set the position of the body to dx and dy done! So what i an interested in is a formula for dx and dy without cloning matrices, scaling the clone around a point, getting dx and dy and finally scale the vertex matrix.

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