Elysian Shadows

Posted: **Sat Nov 22, 2008 3:49 am**

Okay, so I've been working on my game for a little bit now, and I'm just playing around with collision detection. I have a wall (62x244). I want to have it if the player hit's it, he doesn't go anywhere (obvious?). Well, if the player (45x48) hits the wall from the left side, it makes the collision detection. If he hits the bottom, it makes the collision detection. That's all I want so far. Well, I noticed that if you hit the bottom-left corner of the wall, he can walk through it...

Code: Select all

// Hits the left side of the wall...
	if(PlayerX + PlayerW >= WallX && PlayerY >= WallY && PlayerY + PlayerH <= WallY + 244 && PlayerX <= WallX)
	{
		PlayerX -= 1;
	}

	// Hits the top side of the wall...
	if(PlayerY <= WallY + 244 && PlayerX >= WallX && PlayerX + PlayerW <= WallX + 62)
	{
		PlayerY += 1;
	}

Hopefully I can get some help. For those of you who don't know (which I don't see why you would need to know), I'm using C++, and SDL. Alright, thanks (for future reference).

Posted: **Sat Nov 22, 2008 4:51 am**

Collision detection is a non-trivial matter. I think that you're taking a little bit too dirty approach. If you go on like that, after a few walls you won't be able to tell wtf is going on in your code. You should take a more object oriented approach, and maybe check out some tutorials on that.

Posted: **Sat Nov 22, 2008 6:44 am**

I took a lot of time, to find a good way of detecting collision in one of my games (it was more of a learning experience, just to mess around with SDL)

however, simple bounding box collision isn't hard to do at all.
To make simple collison with a single box, it's as easy as checking whether the boxes points have crossed or passed the obstacles. All you have to do is check is the players proximity to the object

A good simple collision tutorial can be found on Lazyfoo.net here http://lazyfoo.net/SDL_tutorials/lesson17/index.php

EDIT: I wrote this really long post, but it was probably a little confusing, as I realised you're not using SDL, so your function will look a little different (should you choose to use a function), to make the link relevant, you could consider declaring a struct or class (struct seemed like the cleanest one to do at the time) to make your PlayerX,PlayerY etc into Player.x,Player.y etc

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typdef struct rect{
 int x; 
 int y; 
 int w; 
 int h;
};

rect Player 
rect Obstacle

now, instead of using SDL Rects as arguments, you can simply pass your own types

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bool Check_Collision(rect Player, rect Obstacle) // this is the collision function in the lazyfoo tutorial, but with user defined //rects as arguments instead of SDL_Rects

bool check_collision( rect A, rect B ) { 
//The sides of the rectangles 
int leftA, leftB; int rightA, rightB;
int topA, topB; int bottomA, bottomB; 

//Calculate the sides of rect A
leftA = A.x; 
rightA = A.x + A.w;
topA = A.y; 
bottomA = A.y + A.h; 
//Calculate the sides of rect B 
leftB = B.x;
rightB = B.x + B.w; 
topB = B.y; 
bottomB = B.y + B.h; 

//If any of the sides from A are outside of B 
if( bottomA <= topB ) 
{
 return false;
 }
if( topA >= bottomB )
{
 return false;
 } 
if( rightA <= leftB )
{
 return false;
 }
if( leftA >= rightB )
{ 
return false;
 } 
//If none of the sides from A are outside B return true;
 }

Now if you want to test for collision for one of your objects, you simply call the function, and it will return true or false, depending on the presence of a collison, if there is one, you can tell your player to move back.

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if(Check_Collision(Player,Obstacle))
{
 // Move player back, whichever way you choose to do it
}

I hope this helped anyway with working out a way to do collision in a simpler way

PS: no credit taken for the code, I found this out from lazyfoo originally, all i've done is change the function so that it accepts user defined rects instead of SDL_Rects

Elysian Shadows

Collison Detection -_-

Collison Detection -_-

Re: Collison Detection -_-

Re: Collison Detection -_-