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# Rectangle Collission Problem

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I'm working on a simple 2D C# and Xna Game similar to the Ice Caves in Pokemon G/S. I've got the Tile classes made and a rudimentary character created but I've hit a snag on the collision detection.

Right now I'm using a custom Rectangle class and a function that tests if 2 rectangles are colliding. Then I use the player's(made out of a separate class) velocity to figure out which side of the tile the player hit. This lets me set the players location to that side, making it look like the tile stopped the player. This works fine for the Left, Right, and top of the tile but when my character hits the bottom side he goes halfway through the tile before he is set to the correct position.

For an Idea of what the game looks like you can go here. [link]http://steveworks.deviantart.com/gallery/#/d2yxt30[/link]

Here's the source.

The Rectangle Class
public class Float_Rectangle    {        public Vector2 TopLeft; // The different vertices of the rectangle instance        public Vector2 TopRight;        public Vector2 Center;        public Vector2 BottomLeft;        public Vector2 BottomRight;        public Float_Rectangle(Vector2 location,Vector2 size)// Creates an instance of float_rectangle        {            TopLeft = location;            TopRight = new Vector2(location.X + (size.X -1), location.Y);            Center = new Vector2((location.X + (size.X-1)) / 2, (location.Y + (size.Y-1)) / 2);            BottomLeft = new Vector2(location.X, location.Y + (size.Y-1));            BottomRight = new Vector2(location.X + (size.X-1), location.Y + (size.Y-1));        }        public void Update_position(Vector2 location, Vector2 size) // Updates the Rectangles postion.        {            TopRight = new Vector2(location.X + (size.X-1), location.Y);            BottomLeft = new Vector2(location.X, location.Y + (size.Y-1));            Center = new Vector2((location.X + (size.X-1)) / 2, (location.Y + (size.Y-1)) / 2);            BottomLeft = new Vector2(location.X, location.Y + (size.Y-1));            BottomRight = new Vector2(location.X + (size.X-1), location.Y + (size.Y-1));        }    }

The collision detection function.
public bool Rect_collide(Float_Rectangle Rect1, Float_Rectangle Rect2)        {            if (Rect1.TopLeft.X >= Rect2.TopLeft.X && Rect1.TopLeft.X <= Rect2.TopRight.X)            {                if (Rect1.TopLeft.Y >= Rect2.TopLeft.Y && Rect1.TopLeft.Y <= Rect2.BottomLeft.Y)                {                    return true;                }            }            if (Rect1.TopRight.X > Rect2.TopLeft.X && Rect1.TopRight.X < Rect2.TopRight.X)            {                if (Rect1.TopRight.Y >= Rect2.TopLeft.Y && Rect1.TopRight.Y  <= Rect2.BottomLeft.Y)                {                    return true;                }            }            if (Rect1.BottomLeft.X >= Rect2.TopLeft.X && Rect1.BottomLeft.X <= Rect2.TopRight.X)            {                if (Rect1.BottomLeft.Y >= Rect2.TopLeft.Y && Rect1.BottomLeft.Y <= Rect2.BottomLeft.Y)                {                    return true;                }            }            if (Rect1.BottomRight.X >= Rect2.TopLeft.X && Rect1.BottomRight.X <= Rect2.TopRight.X)            {                if (Rect1.BottomRight.Y >= Rect2.TopLeft.Y && Rect1.BottomRight.Y <= Rect2.BottomLeft.Y)                {                    return true;                }            }            return false;        }

and the part the simulates a wall.
player.position.X += player.velocity.X;                player.position.Y += player.velocity.Y;                player.rect.Update_position(player.position, new Vector2(32, 32));                foreach (BasicTile Tile in Tiles)                    Tile.update_position();                foreach(BasicTile Tile in Tiles)                {                    if (Rect_collide(player.rect,Tile.rect))                    {                        if (player.velocity.X > 0)                        {                            player.position.X = Tile.rect.TopLeft.X-32;                            player.movement = 1;                            player.velocity.X = 0;                        }                        if (player.velocity.X < 0)                        {                            player.position.X = Tile.rect.TopRight.X+1;                            player.movement = 1;                            player.velocity.X = 0;                        }                        if (player.velocity.Y > 0)                        {                            player.position.Y = Tile.rect.TopLeft.Y - 32;                            player.movement = 1;                            player.velocity.Y = 0;                        }                        if (player.velocity.Y < 0)                        {                            player.position.Y = Tile.rect.BottomLeft.Y+1;                            player.movement = 1;                            player.velocity.Y = 0;                        }                    }                }

[/source]

[Edited by - steveworks on September 26, 2010 9:17:08 PM]

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Have you tried using your debugger for this? It seems like it shouldn't be that difficult to breakpoint when the player is colliding/near-colliding with the bottom and you can see what is going on.

I guess you could just wait around for somebody to help you, but that's more code than I'm willing to sift through :)

If you're not experienced with debugging, this would probably be a good time to learn.

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True. I have next to no experience with Debugging. (I guess I SHOULD take the time to learn that...)

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You should drop whatever else you're doing and learn, you'll be hopeless without it.

Are you using Visual Studio? If you have questions I'm sure either somebody else or myself would be happy to help if you're confused.

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Can you point me towards where I should start?

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That depends on what IDE you have. You didn't answer my question, are you using visual studio? That's probably the most common and most powerful free one.

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Sorry About that. The answer is yes. I'm using microsoft Visual Studio 2010 Express(for windows phone).

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Sorry off the top of my head I don't know any good resources for beginners. Most of the stuff you can figure out just by playing around with it.

You'll want to familiarize yourself with these terms:
Debug Configuration: set this in visual studio to compile for debug mode

breakpoint : you can set these by clicking on the left side of a particular line in the gray area, the code will stop when it reaches this point

watch window: you can see values of variables currently in the watch window, should appear on the bottom when you start debugging

step over : executes the next instruction or function

step into : moves the debugger into the next function to debug that function

What I would do in your case is remove everything in your demo except for the player and one rectangle. Move the player over the rectangle where they are overlapping but your collision detection is not picking it up. Then set a breakpoint after the start of the Rect_collide function. Step through line by line and see if you can spot what isn't working correctly.

Happy hunting!

Thanks. Will do.

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Hey,

Here's basic tutorial how to use the Visual Studio Debugger. It gives you a good idea what you can do.. Using the locals window is going to save you a lot of time!!

Hope it helps:

http://dotnetperls.com/debugging

Cheers,
Bach

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