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Collision between station bricks and a moving ball...

Codejoy · 2003-05-08T19:21:57

Okay so I have this game where there are bricks that act as walls (verticle or horizontal) or if they are a single brick, then just an obsticle.. the bricks are a sqaure of 32x32 pixels, the ball is 8x8 pixels. I can check for the collision between a brick and a ball, no sweat...but I need to know how to see WHAT SIDE of the brick the ball collided with so I can properly reflect the velocity in the x or y direction. The variables of concern are: float Ballx < - balls x position float Bally <- Balls y position float Ballvx <- balls velocity in x float Ballyv <- balls velocity in y brick[current_brick].x <-- bricks x position brick[current_brick].y <-- bricks y position brick[current_brick].width <--width of brick brick[current_brick].height <--height of brick The skeleton of the code looks like: for (int current_brick=0; current_brick<numBricks; current_brick++) { if(Collision(theBall, theBrick[current_brick])==TRUE) { //we collided check which side and set //the proper vx or vy ala Ballvx=-Ballvx etc.. } } I thought this was trivial, but that above part wher u see the comments are wehre I have tried everything i could think of, on paper most my algo's seemed right, in practice the ball would either go through the brick, or reflect back both velocities) I think the underlying problem here is that I use many bricks to make a wall or a barrier to speak. Say like 15 bricks across side by side is a barrier, and 15 bricks down and up is a wall...I think thats why some of my algorithms for reflecting the ball properly havent worked since it was colliding with another brick near the main brick it should of collided with. i.e. |---|---|---| | 1 | 2 | 3 | bricks... |---|---|---| / \ -- where exactly was the collision brick 1 or 2? / [] <-- ball It looks like it hits a corner, but then some case in some part of the algo should just reflect the ball, but i guess its missing that and going right through. I have also used two different kinds of collision algorithms, one to test if the two collided using CollisionBOBs for those who are familiar with Tricks of the Windows Programming Gurus and i tried a different test which says: if(theBall.x+theBall.width > theBrick.x) && (theBall.x < theBrick[i].x+theBrick[i].width) && so on and so on.. Now I thought maybe the collision was getting mis fired because the velocity of the ball in one frame failsto be caught by a case in my collision detectoin, but since the bricks are 32x32 there is no way the ball is travling more than that to exceed a test. I am willing to go with normals here...but how the hell do i do that? I know i could read a lot of articles, but honestly this has taken so much time and im soo behind on this silly game that I dont think id get much out of them in an applicable way... I have had tried to hack some code that LaMothe uses in his Tricks of the Windows Game Programming gurus (more specifically demo13_7.cpp) but that was geared more twards the ball bouncing around inside an irregular shaped polygon, when applied to the regular shaped rectangles here it seems to not work quite as well.. so im at wits end, i need this, I need this bad, and im to the point where I dont care how it works i just want it to work. So if ineed to go with computing normals etc.. how if my object a brick is just defined as, x, y, width, height (an 32x32 bitmap) would i get a normal for each side of it, and how would i compute the normal of my ball (which is essentialy an 8x8 bitmap) If anyone can help, id soo greatly appreciate this its not even funny. This is the only thing holding my whole game up, I thought it was trivial, after posting here a while back and getting no responses that worked (Was in beginners section) and asking some friends to help, still today it isnt working. Thanks for any help as im really at my wits end bout this, Shane [edited by - Codejoy on May 8, 2003 9:44:11 AM]

General and Gameplay Programming Programming

Started by Codejoy May 07, 2003 04:51 PM

12 comments, last by Codejoy 20 years, 11 months ago

Rob Loach

1,504

May 08, 2003 02:06 PM

Hint: Use the ball''s radius.

- Rob Loach
Current Project: Go Through Object-Oriented Programming in C++ by Robert Lafore

"Do or do not. There is no try."
- Yoda

Rob Loach [Website] [Projects] [Contact]

Codejoy

122

Author

May 08, 2003 02:12 PM

hmmmm get a vector to the bricka nd just see if its length is less than the balls radius?

-Shane

Anonymous

May 08, 2003 02:44 PM

Determine the quantum probability of the bricks edge existing over top of the balls edge, and then calculate a new probility field for both brick and ball based all of the itty bitty atomic and electromagnetic interactions, and update the respective positions accordingly. I think this is how Arkanoid did it.

Mage2k

336

May 08, 2003 07:21 PM

Hmm... as far as the corner problem with the ball colliding with more than one brick goes, why not check for collisions with all bricks within a certain radius from them ball (to cut down on the # of collision tests), but don''t respond to a collision immediately, instead put all of the bricks that a collision is detected with into a list and once you have finished all of your collision tests, use some kind of heuristic to determine which brick to use for processing your collision response.

---------------------------------------------------There are 10 kinds of people in the world:Those that understand binary, and those that dont...Mage

Collision between station bricks and a moving ball...

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Collision between station bricks and a moving ball...

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