Hi, I know this might have already been made, but I really need it bad. I started, about a month ago, a game called OpenSS (Open-Side-Scroller), and I''m pretty much started. I''m at a point where I need one important thing : Collision detection! I''m not looking for a complex one, since OpenSS will be used for old-skool side scrollers, just like SMB3 on the Nes. So, all the physics are "done", it jumps (but doesn''t lands), accelerates on the X-Axis, but there''s NO collision detection! The way the game works is like this : There''s a bg layer (will be EZ to do) There''s a tile grid (where the brick blocks, ? Blocks, floor and the like) are located There''s a "sprite layer", where all sprites (char, allies (pals over the net), enemies, etc) will go So I first get the tiles in which the char is, and then I need to check if there''s a collision. I want to look at my code, here it is : (da sprite struct starts here) struct SPRITE_STRUCT { int SizeX; int SizeY; int TileTL; /* [-V989] In the next four lines, the vars are used to check if there is a collision */ int TileTR; /* [-V989] TL is for Top left, BR if for bottom right, and so on... */ int TileBL; int TileBR; int XDirection; int YDirection; int AnimFrame; int MaxFrames; /* [-V989] Will be something like "GetMaxFrames()" */ CHAR SubType; /* [-V989] ex Fire Mario, Super Mario, etc */ FLOAT fPosX; FLOAT fPosY; FLOAT fVelX; FLOAT fVelY; }; (da physics start here) VOID UpdateSprite( SPRITE_STRUCT* pSprite, FLOAT fTimeDelta ) { /* [-V989] Since, for the X axis, right is positive and left is negative... Hard to explain =:0( , but just try to think about it... */ pSprite->XDirection = KeyRight-KeyLeft; pSprite->YDirection = KeyDown-KeyUp; /* [-V989] Calculate the X momentum */ float MaxSpeed = 200; float AccelSpeed = 1; float BrakeSpeed = 6; float SlowDownSpeed = 3; float daifrule; /* [-V989] It uses an simple math rule, -*- and +*+ always give +, while the others give - */ if(pSprite->fVelX!=0) daifrule = pSprite->XDirection * pSprite->fVelX; else daifrule = pSprite->XDirection * pSprite->fVelX+1; /* [-V989] "fVelX+1" is there to make sure it''s not the velocity who makes the result a 0 */ if((KeyRight || KeyLeft)) { if(daifrule<0) /* [-V989] if they are not in the same way, it will result as a - */ pSprite->fVelX+=(pSprite->XDirection * (BrakeSpeed * (fTimeDelta * 100))); if(daifrule>0) /* [-V989] if they are in the same way, it will be a + */ pSprite->fVelX+=(pSprite->XDirection * (AccelSpeed * (fTimeDelta * 100))); } if(!KeyRight && !KeyLeft) /* [-V989] No key is pressed, slow down... */ { if(pSprite->fVelX > 0) pSprite->fVelX-=SlowDownSpeed * (fTimeDelta * 100); else if(pSprite->fVelX < 0) pSprite->fVelX+=SlowDownSpeed * fTimeDelta * 100; } /* [-V989] Make sure they are in a certain speed range */ if(pSprite->fVelX < 1 && pSprite->fVelX > 0) pSprite->fVelX = 0; if(pSprite->fVelX > -1 && pSprite->fVelX < 0) pSprite->fVelX = 0; if(pSprite->fVelX > MaxSpeed) pSprite->fVelX = MaxSpeed; if(pSprite->fVelX < -MaxSpeed) pSprite->fVelX = -MaxSpeed; /* [-V989] Calculate the Y momentum. It only uses basic physics, and might be made better someday, if needed... */ const int InitSpeed = 200; const float GravAccel = -9.8; /* [-V989] The earth is 9.8 , the moon is 1.6 */ if(KeyUp && pSprite->fVelY == 0) pSprite->fVelY = -InitSpeed; else if(KeyUp && pSprite->fVelY < 0) pSprite->fVelY -= ((GravAccel * fTimeDelta * 100) / 2); else if ((!KeyUp && pSprite->fVelY < 0) || (pSprite->fVelY > 0)) pSprite->fVelY -= (GravAccel * fTimeDelta * 100); /* [-V989] Temporary Debugging-related function, to reset the important vars that are being made...*/ if(KeySpace) { pSprite->fVelY = 0; pSprite->fVelX = 0; pSprite->fPosX = 320; pSprite->fPosY = 240; } /* [-V989] Basic Collision detection */ /* [-V989] Check if the sprite is within the screen boundaries */ if(pSprite->fPosY > SCREEN_HEIGHT - (int) TileDiam) { pSprite->fPosY = SCREEN_HEIGHT - (int) TileDiam; pSprite->fVelY = 0; KeyUp = 0; } /* [-V989] Check if the sprite is overlapping a tile, and if it is, then get "out" of the tile */ (physics code will be here) /* [-V989] Update the sprite(s) position(s) after checking if they are not overlapping a OBJ */ int checkall=1; if(checkall) pSprite->fPosX += pSprite->fVelX * fTimeDelta; if(checkall) pSprite->fPosY += pSprite->fVelY * fTimeDelta; /* [-V989] Will be used for the anims, might be implemented soon... */ // pSprite->MaxFrames=2; /* [-V989] "=2" will be replaced by something like "=GetMaxFrames(state,...) */ // Animcntr+=fTimeDelta; // if(Animcntr>1.000) Animcntr-=1.000; // for(int i = 1; i < pSprite->MaxFrames; i++) // { // if((Animcntr/i)>(1/pSprite->MaxFrames)) pSprite->AnimFrame = i; // } } (end of my code bits!) Sorry if it''s a long read, but I put it here so that you can see how it works... If you need help to read my code, just ask me, and I will explain it the best I can! =:0) - ViNcE989, founder and coder of OpenSS

Programming a sprite library myself.

I built the collision detection algos around
this article by John Amato:

http://www.gamedev.net/reference/articles/article735.asp

It explains everything from rectangular detection to
Sprite on Sprite pixel level detection.

I however used BOOL bitmasks, and even the pixel level
detectors are fairly quick.

Guy