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  • Displaying recntangles in game window with XNA

    - by blerh
    I want to divide my game grid into an array of rectangles. Each rectangle is 40x40 and there are 14 rectangles in every column, with a total of 25 columns. This covers a game area of 560x1000. This is the code I have set up to make the first column of rectangles on the game grid: Rectangle[] gameTiles = new Rectangle[15]; for (int i = 0; i <= 15; i++) { gameTiles[i] = new Rectangle(0, i * 40, 40, 40); } I'm pretty sure this works, but of course I cannot confirm it because rectangles do not render on the screen for me to physically see them. What I would like to do for debugging purposes is to render a border, or fill the rectangle with color so I can see it on the game itself, just to make sure this works. Is there a way to make this happen? Or any relatively simple way I can just make sure that this works? Thank you very much.

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  • Attempting to find a formula for tessellating rectangles onto a board, where middle square can't be

    - by timemirror
    I'm working on a spatial stacking problem... at the moment I'm trying to solve in 2D but will eventually have to make this work in 3D. I divide up space into n x n squares around a central block, therefore n is always odd... and I'm trying to find the number of locations that a rectangle of any dimension less than n x n (eg 1x1, 1x2, 2x2 etc) can be placed, where the middle square is not available. So far I've got this.. total number of rectangles = ((n^2 + n)^2 ) / 4 ..also the total number of squares = (n (n+1) (2n+1)) / 6 However I'm stuck in working out a formula to find how many of those locations are impossible as the middle square would be occupied. So for example: [] [] [] [] [x] [] [] [] [] 3 x 3 board... with 8 possible locations for storing stuff as mid square is in use. I can use 1x1 shapes, 1x2 shapes, 2x1, 3x1, etc... Formula gives me the number of rectangles as: (9+3)^2 / 4 = 144/4 = 36 stacking locations However as the middle square is unoccupiable these can not all be realized. By hand I can see that these are impossible options: 1x1 shapes = 1 impossible (mid square) 2x1 shapes = 4 impossible (anything which uses mid square) 3x1 = 2 impossible 2x2 = 4 impossible etc Total impossible combinations = 16 Therefore the solution I'm after is 36-16 = 20 possible rectangular stacking locations on a 3x3 board. I've coded this in C# to solve it through trial and error, but I'm really after a formula as I want to solve for massive values of n, and also to eventually make this 3D. Can anyone point me to any formulas for these kind of spatial / tessellation problem? Also any idea on how to take the total rectangle formula into 3D very welcome! Thanks!

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  • How do i pack multiple rectangles in a 2d box tetris style

    - by mglmnc
    I have a number of rectangles of various widths and heights. I have a larger rectangular platform to put them on. I want to pack them on one side of the platform so they spread in the lengthwise (X) dimension but keep the widthwise (Y) dimension to a minimal. That is to place them like a tetris game. There can be no overlaps but there can be gaps. Is there an algorithm out there to do this?

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  • Collision Detection for arbitrarily sized, positioned and rotated rectangles in XNA

    - by Stefan
    I'm working with xna in C# and in my game I will have a variety of space ships flying all over the place. They will each have an arbitrary rotation, size and position in space and I need a method to determine when they collide. Ideally the method would take two Rectangles, two doubles and two Vector2s for size, rotation and position respectively and return a boolean that indicates whether they have intersected or not.

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  • Grouping rectangles (getting the bounding boxes of rects)

    - by hyn
    What is a good, fast way to get the "final" bounding boxes of a set of random (up to about 40, not many) rectangles? By final I mean that all bounding boxes don't intersect with any other. Brute force way: in a double for loop, for each rect, test for intersection against every other rect. The intersecting rects become a new rect (replaced), indicating the bounding box. Start over and repeat until no intersection is detected. Because the rects are random every time, and the rect count is relatively small, collision detection using spatial hashing seems like overkill. Is there a way to do this more effectively?

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  • How to draw multiple rectangles using c#

    - by Nivas
    I have drawn and saved the Rectangle on the image i loaded in the picture box. How i like to draw multiple rectangles for that i tried array in the rectangle but it gives error ("Object reference not set to an instance of an object." (Null reference Exception was unhandled). private void pictureBox1_MouseDown(object sender, MouseEventArgs e) { if (mybitmap == null) { mybitmap = new Bitmap(sz.Width, sz.Height); } rect[count] = new Rectangle(e.X, e.Y, 0, 0); this.Invalidate(); } private void pictureBox1_MouseMove(object sender, MouseEventArgs e) { if (stayToolStripMenuItem.Checked == true) { switch (e.Button) { case MouseButtons.Left: { rect[count] = new Rectangle(rect[count].Left, rect[count].Top, e.X - rect[count].Left, e.Y - rect[count].Top); pictureBox1.Invalidate(); count++: break; } } } } private void pictureBox1_Paint(object sender, PaintEventArgs e) { if (stayToolStripMenuItem.Checked == true) { button1.Visible = true; button2.Visible = true; if (mybitmap == null) { return; } using (g = Graphics.FromImage(mybitmap)) { using (Pen pen = new Pen(Color.Red, 2)) { //g.Clear(Color.Transparent); e.Graphics.DrawRectangle(pen, rect); label1.Top = rect[count].Top; label1[count].Left = rect[count].Left; label1.Width = rect[count].Width; label1.Height = rect[count].Height; if (label1.TextAlign == ContentAlignment.TopLeft) { e.Graphics.DrawString(label1.Text, label1.Font, new SolidBrush(label1.ForeColor), rect); g.DrawString(label1.Text, label1.Font, new SolidBrush(label1.ForeColor), rect); g.DrawRectangle(pen, rect[count]); } } } } } How can i do this.....

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  • How to draw mutiple rectangles using c#

    - by Nivas
    I have drawn and saved the Rectangle on the image i loaded in the picture box. How i like to draw multiple rectangles for that i tried array in the rectangle but it gives error ("Object reference not set to an instance of an object." (Null reference Exception was unhandled). enter code here private void pictureBox1_MouseDown(object sender, MouseEventArgs e) { if (mybitmap == null) { mybitmap = new Bitmap(sz.Width, sz.Height); } rect = new Rectangle(e.X, e.Y, 0, 0); this.Invalidate(); } private void pictureBox1_MouseMove(object sender, MouseEventArgs e) { if (stayToolStripMenuItem.Checked == true) { switch (e.Button) { case MouseButtons.Left: { rect = new Rectangle(rect.Left, rect.Top, e.X - rect.Left, e.Y - rect.Top); pictureBox1.Invalidate(); break; } } } } private void pictureBox1_Paint(object sender, PaintEventArgs e) { if (stayToolStripMenuItem.Checked == true) { button1.Visible = true; button2.Visible = true; if (mybitmap == null) { return; } using (g = Graphics.FromImage(mybitmap)) { using (Pen pen = new Pen(Color.Red, 2)) { //g.Clear(Color.Transparent); e.Graphics.DrawRectangle(pen, rect); label1.Top = rect.Top; label1.Left = rect.Left; label1.Width = rect.Width; label1.Height = rect.Height; if (label1.TextAlign == ContentAlignment.TopLeft) { e.Graphics.DrawString(label1.Text, label1.Font, new SolidBrush(label1.ForeColor), rect); g.DrawString(label1.Text, label1.Font, new SolidBrush(label1.ForeColor), rect); g.DrawRectangle(pen, rect); } } } } } How can i do this.....

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  • Snake game, can't add new rectangles?

    - by user1814358
    I had seen some problem on other forum, and i tried to solve them but unsuccesfully, now is too intersting for me and i just need to solve this for my ego... lol Main problem is when snake eat first food, snake added one rectangle, when snake eat second food nothings changed? When snake head position and food position are same, then i try to add another rectangle, i have list where i stored rectangles coordinates x and y. What do you think, how i can to solve this problem? I think that i'm so close, but my brain has stopped. :( code: using System; using System.Collections.Generic; using System.ComponentModel; using System.Data; using System.Drawing; using System.Linq; using System.Text; using System.Windows.Forms; namespace Zmijice { enum Kontrole { Desno,Levo,Gore,Dole,Stoj } public partial class Zmijice : Form { int koox; int kooy; private int x; private int y; private int c; private int b; private const int visina=20; //width private const int sirina=20; //height //private int m = 20; //private int n = 20; private List<int> SegmentX = new List<int>(); private List<int> SegmentY = new List<int>(); Random rnd = new Random(); private Kontrole Pozicija; public Zmijice() { InitializeComponent(); //slucajne pozicije pri startu x = rnd.Next(1, 20) * 20; y = rnd.Next(1, 20) * 20; c = rnd.Next(1, 20) * 20; b = rnd.Next(1, 20) * 20; Pozicija = Kontrole.Stoj; //stop on start } private void Tajmer_Tick(object sender, EventArgs e) { if (Pozicija == Kontrole.Stoj) { //none } if (Pozicija == Kontrole.Desno) { x += 20; } else if (Pozicija == Kontrole.Levo) { x -= 20; } else if (Pozicija == Kontrole.Gore) { y -= 20; } else if (Pozicija == Kontrole.Dole) { y += 20; } Invalidate(); } private void Zmijice_KeyDown(object sender, KeyEventArgs e) { if (e.KeyCode == Keys.Down) { Pozicija = Kontrole.Dole; } else if (e.KeyCode == Keys.Up) { Pozicija = Kontrole.Gore; } else if (e.KeyCode == Keys.Right) { Pozicija = Kontrole.Desno; } else if (e.KeyCode == Keys.Left) { Pozicija = Kontrole.Levo; } } private void Zmijice_Paint(object sender, PaintEventArgs e) { int counter = 1; //ako je pojela hranu if (x==c && y==b) { counter++; c = rnd.Next(1, 20); //nova pozicija hrrane c = c * 20; b = rnd.Next(1, 20); b = b * 20; //povecaj zmijicu SegmentX.Add(x); SegmentY.Add(y); //label1.Text = SegmentX.Count().ToString() + " " + SegmentY.Count().ToString(); //left if (Pozicija == Kontrole.Levo) { koox = x+20; kooy = y; } //right if (Pozicija == Kontrole.Desno) { koox = x-20; kooy = y; } //up if (Pozicija == Kontrole.Gore) { koox = x; kooy = y+20; } //down if (Pozicija == Kontrole.Dole) { koox = x; kooy = y-20; } } foreach (int k in SegmentX) { foreach (int l in SegmentY) { e.Graphics.FillRectangle(Brushes.Orange, koox, kooy, sirina, visina); } } koox = x; kooy = y; e.Graphics.FillRectangle(Brushes.DarkRed, x, y, sirina, visina); e.Graphics.FillRectangle(Brushes.Aqua, c, b, sirina, visina); } } }

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  • Partition a rectangle into near-squares of given areas

    - by Marko Dumic
    I have a set of N positive numbers, and a rectangle of dimensions X and Y that I need to partition it in N smaller rectangles such that: the surface area of each smaller rectangle is proportional to it's corresponding number in given set all space of big rectangle is occupied and there is no leftover space between smaller rectangles each small rectangle should be shaped as close to square as feasible the execution time should be reasonably small I need directions on this. Do you know of such algorithm described on the web? Do you have any ideas (pseudo-code is fine)? Thanks.

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  • c# winforms - scrollable panel with rectangles

    - by Peanut
    Hi, I'm new to winforms and have tried to track down an answer to the following with no luck ... I have a panel in winforms and add to it a Rectangle that is wider than the panel itself. I've set the panel AutoScroll property to true however the panels horizontal scrollbar never appears. Why is this? And how do I get the scrollbar to scroll? Here is my code to add the rectangle: private void panel1_Paint(object sender, PaintEventArgs e) { Graphics g = e.Graphics; Rectangle rec = new Rectangle(2, 2, 400, 40); g.DrawRectangle(new Pen(Color.Black), rec); g.FillRectangle(new SolidBrush(Color.Blue), rec); } If I add a Label control to the panel and give it a text value that will go beyond the bounds of the panel - then the autoscroll works, but just not for a rectangle. Many thanks.

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  • Drawing rectangles on a grid in a web browser

    - by Dhruv
    I would like to create an online, simple WYSIWYG drawing editor allowing people to draw rectangular shapes. I'm thinking of a grid which the lines and points can snap on to, ensuring that the lines are strictly vertical or horizontal. I will be parsing the rectangular shapes to obtain some area calculations and compute certain things. How can I achieve the drawing ability? The new canvas tag is good but people have been telling me that IE does not support it. I found some Java applets but I have never programmed in Java before. Is there a way to do this using pure javascript or jquery? Does ASP.NET help at all? Thanks.

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  • Tiling rectangles seamlessly in WPF while maintaing subpixel accuracy?

    - by Jens
    I have had the problem described in the question Tiling rectangles seamlessly in WPF, but am not really happy with the answers given there. I am painting a bar chart by painting lots of rectangles right next to each other. Depending on the scale of the canvas containing them, there are small gaps visible between some of them as a result from sub-pixel rendering. I learned from the above question how to make my rectangles fit with the screen pixels, removing that effect. Unfortunately, my chart may display way more bars than there are pixels. Apart from the tiny gaps (which manifest as a periodic change in color saturation), this works well. If I snap each bar with the screen pixels, most of the bars vanish, though, so I am looking for another solution. Thanks in advance!

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  • How can I group an array of rectangles into "Islands" of connected regions?

    - by Eric
    The problem I have an array of java.awt.Rectangles. For those who are not familiar with this class, the important piece of information is that they provide an .intersects(Rectangle b) function. I would like to write a function that takes this array of Rectangles, and breaks it up into groups of connected rectangles. Lets say for example, that these are my rectangles (constructor takes the arguments x, y, width,height): Rectangle[] rects = new Rectangle[] { new Rectangle(0, 0, 4, 2), //A new Rectangle(1, 1, 2, 4), //B new Rectangle(0, 4, 8, 2), //C new Rectangle(6, 0, 2, 2) //D } A quick drawing shows that A intersects B and B intersects C. D intersects nothing. A tediously drawn piece of ascii art does the job too: +-------+ +---+ ¦A+---+ ¦ ¦ D ¦ +-+---+-+ +---+ ¦ B ¦ +-+---+---------+ ¦ +---+ C ¦ +---------------+ Therefore, the output of my function should be: new Rectangle[][]{ new Rectangle[] {A,B,C}, new Rectangle[] {D} } The failed code This was my attempt at solving the problem: public List<Rectangle> getIntersections(ArrayList<Rectangle> list, Rectangle r) { List<Rectangle> intersections = new ArrayList<Rectangle>(); for(Rectangle rect : list) { if(r.intersects(rect)) { list.remove(rect); intersections.add(rect); intersections.addAll(getIntersections(list, rect)); } } return intersections; } public List<List<Rectangle>> mergeIntersectingRects(Rectangle... rectArray) { List<Rectangle> allRects = new ArrayList<Rectangle>(rectArray); List<List<Rectangle>> groups = new ArrayList<ArrayList<Rectangle>>(); for(Rectangle rect : allRects) { allRects.remove(rect); ArrayList<Rectangle> group = getIntersections(allRects, rect); group.add(rect); groups.add(group); } return groups; } Unfortunately, there seems to be an infinite recursion loop going on here. My uneducated guess would be that java does not like me doing this: for(Rectangle rect : allRects) { allRects.remove(rect); //... } Can anyone shed some light on the issue?

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  • Whats a good way to do Collision with 2D Rectangles? can someone give me a tip?

    - by Javier
    using System; using System.Collections.Generic; using System.Linq; using System.Text; using Microsoft.Xna.Framework; namespace BreakOut { class Field { public static Field generateField() { List<Block> blocks = new List<Block>(); for (int j = 0; j < BlockType.BLOCK_TYPES.Length; j++) for (int i = 0; i < (Game1.WIDTH / Block.WIDTH); i++) { Block b = new Block(BlockType.BLOCK_TYPES[j], new Vector2(i * Block.WIDTH, (Block.HEIGHT + 2) * j + 5)); blocks.Add(b); } return new Field(blocks); } List<Block> blocks; public Field(List<Block> blocks) { this.blocks = blocks; } public void Update(GameTime gameTime, Ball b) { List<Block> removals = new List<Block>(); foreach (Block o in blocks) { if (o.BoundingBox.Intersects(new Rectangle((int)b.pos.X, (int)b.pos.Y, Ball.WIDTH, Ball.HEIGHT))) //collision with blocks { removals.Add(o); } } foreach(Block o in removals) blocks.Remove(o); //removes the blocks, but i need help hitting one at a time } public void Draw(GameTime gameTime) { foreach (Block b in blocks) b.Draw(gameTime); } } } My problem is that My collision in this sucks. I'm trying to add collision with a ball and hitting against a block and then one of the blocks dissapear. The problem i'm having is: When the ball hits the block, it removes it all in one instance. Please people don't be mean and say mean answers to me, im just in highschool, still a nooby and trying to learn more c#/XNA..

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  • How can I get accurate collision resolution on the corners of rectangles?

    - by ssb
    I have a working collision system implemented, and it's based on minimum translation vectors. This works fine in most cases except when the minimum translation vector is not actually in the direction of the collision. For example: When a rectangle is on the far edge on any side of another rectangle, a force can be applied, in this example down, the pushes one rectangle into the other, particularly a static object like a wall or a floor. As in the picture, the collision is coming from above, but because it's on the very edge, it translates to the left instead of back up. I've searched for a while to find an approach but everything I can find deals with general corner collisions where my problem is only in this one limited case. Any suggestions?

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  • Collision Detection in Java for a game

    - by gordsmash
    Im making a game in Java with a few other people but we are stuck on one part of it, making the collision detection. The game is an RPG and I know how to do the collision detection with the characters using Rectangles, but what I dont know how to do is the collision detection for the maps. What I mean by that is like so the character cant walk over trees or water and that stuff but using rectangles doesnt seem like the best option here. Well to explain what the game maps are gonna look like, here is an example http://i980.photobucket.com/albums/ae287/gordsmash/7-8.jpg Now I could use rectangles to get bounds and stop the player from walking over the trees and water but that would take a lot of them. But is there another easier way to prevent the player from walking over the trees and obstacles besides using Rectangles?

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  • 2D collision resolving

    - by Philippe Paré
    I've just worked out an AABB collision algorithm for my 2D game and I was very satisfied until I found out it only works properly with movements of 1 in X and 1 in Y... here it is: public bool Intersects(Rectanglef rectangle) { return this.Left < rectangle.Right && this.Right > rectangle.Left && this.Top < rectangle.Bottom && this.Bottom > rectangle.Top; } public bool IntersectsAny(params Rectanglef[] rectangles) { for (int i = 0; i < rectangles.Length; i++) { if (this.Left < rectangles[i].Right && this.Right > rectangles[i].Left && this.Top < rectangles[i].Bottom && this.Bottom > rectangles[i].Top) return true; } return false; } and here is how I use it in the update function of my player : public void Update(GameTime gameTime) { Rectanglef nextPosX = new Rectanglef(AABB.X, AABB.Y, AABB.Width, AABB.Height); Rectanglef nextPosY; if (Input.Key(Key.Left)) nextPosX.X--; if (Input.Key(Key.Right)) nextPosX.X++; bool xFree = !nextPosX.IntersectsAny(Boxes.ToArray()); if (xFree) nextPosY = new Rectanglef(nextPosX.X, nextPosX.Y, nextPosX.Width, nextPosX.Height); else nextPosY = new Rectanglef(AABB.X, AABB.Y, AABB.Width, AABB.Height); if (Input.Key(Key.Up)) nextPosY.Y--; if (Input.Key(Key.Down)) nextPosY.Y++; bool yFree = !nextPosY.IntersectsAny(Boxes.ToArray()); if (yFree) AABB = nextPosY; else if (xFree) AABB = nextPosX; } What I'm having trouble with, is a system where I can give float values to my movement and make it so there's a smooth acceleration. Do I have to retrieve the collision rectangle (the rectangle created by the other two colliding)? or should I do some sort of vector and go along this axis until I reach the collision? Thanks a lot!

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  • Detect rotated rectangle collision

    - by handyface
    I'm trying to implement a script that detects whether two rotated rectangles collide for my game. 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!

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  • Drawing problem does ShowWindow(hWnd, SW_HIDE) automatically invalidate rectangles?

    - by wk1989
    Hello, I'm running into a problem where, I have a Window that contains a child window. The child window contains another child window where a video is playing using Windows Media Player. Whenever I do call ShowWindow (hWnd, SW_HIDE) on the parent Window and paint over the entire surface, the region occupied by the grand-child window (where the video was playing) is not overridden. I used spy++ and found that that region which was not overridden was set to hidden BEFORE the repaint occurs. I monitored the hwnd of the grand-child window and it did not seem to receive any WM_EraseBKGND or WM_NCPAINT messages. Does this mean the area it occupied had not been invalidated and therefore could not be drawn over? I'm new to winforms. Thanks!

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  • Winform not scrolling when drawing objects on it

    - by dezkev
    Hello All, C#3.0,.net framework 3.5 I am drawing ( using the draw method in the graphics class) a lot of solid rectangles on a windows form vertically. The form starts at 500 x 500 px and the rectangles are only drawn at runtime after data is downloaded from the net -and the number of rectangles depends on the download so I do not know it upfront. So only a few rectangles are drawn as the size of the form is fixed. So I googled/Binged ( lest someone suggest I do that) and found a few tips but they don't work in this case -like setting the forms AutoScroll property to true or trying double buffering.I also tried to draw on a listbox control and set it's scroll property etc...but no dice. I'm guessing there is no way to display , say 200 rectangles vertically on a windows form using draw. I need some other solution... any ideas please. Maybe a list of pictureboxes and then populate each picturebox with the solid color ? Thanks

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  • C#/.NET Little Wonders: Use Cast() and TypeOf() to Change Sequence Type

    - by James Michael Hare
    Once again, in this series of posts I look at the parts of the .NET Framework that may seem trivial, but can help improve your code by making it easier to write and maintain. The index of all my past little wonders posts can be found here. We’ve seen how the Select() extension method lets you project a sequence from one type to a new type which is handy for getting just parts of items, or building new items.  But what happens when the items in the sequence are already the type you want, but the sequence itself is typed to an interface or super-type instead of the sub-type you need? For example, you may have a sequence of Rectangle stored in an IEnumerable<Shape> and want to consider it an IEnumerable<Rectangle> sequence instead.  Today we’ll look at two handy extension methods, Cast<TResult>() and OfType<TResult>() which help you with this task. Cast<TResult>() – Attempt to cast all items to type TResult So, the first thing we can do would be to attempt to create a sequence of TResult from every item in the source sequence.  Typically we’d do this if we had an IEnumerable<T> where we knew that every item was actually a TResult where TResult inherits/implements T. For example, assume the typical Shape example classes: 1: // abstract base class 2: public abstract class Shape { } 3:  4: // a basic rectangle 5: public class Rectangle : Shape 6: { 7: public int Widtgh { get; set; } 8: public int Height { get; set; } 9: } And let’s assume we have a sequence of Shape where every Shape is a Rectangle… 1: var shapes = new List<Shape> 2: { 3: new Rectangle { Width = 3, Height = 5 }, 4: new Rectangle { Width = 10, Height = 13 }, 5: // ... 6: }; To get the sequence of Shape as a sequence of Rectangle, of course, we could use a Select() clause, such as: 1: // select each Shape, cast it to Rectangle 2: var rectangles = shapes 3: .Select(s => (Rectangle)s) 4: .ToList(); But that’s a bit verbose, and fortunately there is already a facility built in and ready to use in the form of the Cast<TResult>() extension method: 1: // cast each item to Rectangle and store in a List<Rectangle> 2: var rectangles = shapes 3: .Cast<Rectangle>() 4: .ToList(); However, we should note that if anything in the list cannot be cast to a Rectangle, you will get an InvalidCastException thrown at runtime.  Thus, if our Shape sequence had a Circle in it, the call to Cast<Rectangle>() would have failed.  As such, you should only do this when you are reasonably sure of what the sequence actually contains (or are willing to handle an exception if you’re wrong). Another handy use of Cast<TResult>() is using it to convert an IEnumerable to an IEnumerable<T>.  If you look at the signature, you’ll see that the Cast<TResult>() extension method actually extends the older, object-based IEnumerable interface instead of the newer, generic IEnumerable<T>.  This is your gateway method for being able to use LINQ on older, non-generic sequences.  For example, consider the following: 1: // the older, non-generic collections are sequence of object 2: var shapes = new ArrayList 3: { 4: new Rectangle { Width = 3, Height = 13 }, 5: new Rectangle { Width = 10, Height = 20 }, 6: // ... 7: }; Since this is an older, object based collection, we cannot use the LINQ extension methods on it directly.  For example, if I wanted to query the Shape sequence for only those Rectangles whose Width is > 5, I can’t do this: 1: // compiler error, Where() operates on IEnumerable<T>, not IEnumerable 2: var bigRectangles = shapes.Where(r => r.Width > 5); However, I can use Cast<Rectangle>() to treat my ArrayList as an IEnumerable<Rectangle> and then do the query! 1: // ah, that’s better! 2: var bigRectangles = shapes.Cast<Rectangle>().Where(r => r.Width > 5); Or, if you prefer, in LINQ query expression syntax: 1: var bigRectangles = from s in shapes.Cast<Rectangle>() 2: where s.Width > 5 3: select s; One quick warning: Cast<TResult>() only attempts to cast, it won’t perform a cast conversion.  That is, consider this: 1: var intList = new List<int> { 1, 1, 2, 3, 5, 8, 13, 21, 34, 55, 89 }; 2:  3: // casting ints to longs, this should work, right? 4: var asLong = intList.Cast<long>().ToList(); Will the code above work?  No, you’ll get a InvalidCastException. Remember that Cast<TResult>() is an extension of IEnumerable, thus it is a sequence of object, which means that it will box every int as an object as it enumerates over it, and there is no cast conversion from object to long, and thus the cast fails.  In other words, a cast from int to long will succeed because there is a conversion from int to long.  But a cast from int to object to long will not, because you can only unbox an item by casting it to its exact type. For more information on why cast-converting boxed values doesn’t work, see this post on The Dangers of Casting Boxed Values (here). OfType<TResult>() – Filter sequence to only items of type TResult So, we’ve seen how we can use Cast<TResult>() to change the type of our sequence, when we expect all the items of the sequence to be of a specific type.  But what do we do when a sequence contains many different types, and we are only concerned with a subset of a given type? For example, what if a sequence of Shape contains Rectangle and Circle instances, and we just want to select all of the Rectangle instances?  Well, let’s say we had this sequence of Shape: 1: var shapes = new List<Shape> 2: { 3: new Rectangle { Width = 3, Height = 5 }, 4: new Rectangle { Width = 10, Height = 13 }, 5: new Circle { Radius = 10 }, 6: new Square { Side = 13 }, 7: // ... 8: }; Well, we could get the rectangles using Select(), like: 1: var onlyRectangles = shapes.Where(s => s is Rectangle).ToList(); But fortunately, an easier way has already been written for us in the form of the OfType<T>() extension method: 1: // returns only a sequence of the shapes that are Rectangles 2: var onlyRectangles = shapes.OfType<Rectangle>().ToList(); Now we have a sequence of only the Rectangles in the original sequence, we can also use this to chain other queries that depend on Rectangles, such as: 1: // select only Rectangles, then filter to only those more than 2: // 5 units wide... 3: var onlyBigRectangles = shapes.OfType<Rectangle>() 4: .Where(r => r.Width > 5) 5: .ToList(); The OfType<Rectangle>() will filter the sequence to only the items that are of type Rectangle (or a subclass of it), and that results in an IEnumerable<Rectangle>, we can then apply the other LINQ extension methods to query that list further. Just as Cast<TResult>() is an extension method on IEnumerable (and not IEnumerable<T>), the same is true for OfType<T>().  This means that you can use OfType<TResult>() on object-based collections as well. For example, given an ArrayList containing Shapes, as below: 1: // object-based collections are a sequence of object 2: var shapes = new ArrayList 3: { 4: new Rectangle { Width = 3, Height = 5 }, 5: new Rectangle { Width = 10, Height = 13 }, 6: new Circle { Radius = 10 }, 7: new Square { Side = 13 }, 8: // ... 9: }; We can use OfType<Rectangle> to filter the sequence to only Rectangle items (and subclasses), and then chain other LINQ expressions, since we will then be of type IEnumerable<Rectangle>: 1: // OfType() converts the sequence of object to a new sequence 2: // containing only Rectangle or sub-types of Rectangle. 3: var onlyBigRectangles = shapes.OfType<Rectangle>() 4: .Where(r => r.Width > 5) 5: .ToList(); Summary So now we’ve seen two different ways to get a sequence of a superclass or interface down to a more specific sequence of a subclass or implementation.  The Cast<TResult>() method casts every item in the source sequence to type TResult, and the OfType<TResult>() method selects only those items in the source sequence that are of type TResult. You can use these to downcast sequences, or adapt older types and sequences that only implement IEnumerable (such as DataTable, ArrayList, etc.). Technorati Tags: C#,CSharp,.NET,LINQ,Little Wonders,TypeOf,Cast,IEnumerable<T>

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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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