can someone tell me why this doesn't work right?
BlitzMax Forums/BlitzMax Beginners Area/can someone tell me why this doesn't work right?
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| Here's a simple pong game I started. Sometimes the ball goes right through the paddle though and I have no idea why. I was hoping someone could help me. Local X=320,Y=240,D1,b=1 ' coordinates of ball, direction of ball, game state (ball in motion/not in motion) Local y2 'player 1 Local y3 = 200 'computer player center screen Graphics 640,480 While Not KeyDown(Key_Escape)'keeps game on screen (everything is programmed within this loop) If B=1 Then D1=6 Y2=200 'triggers ball reset. player 1 paddle is centered DrawOval x,y,8,8 'ball is drawn on screen DrawRect 0, y2, 5, 80 'player 1 paddle DrawRect 635, y3, 5, 80'computer paddle If Y -36 > Y3 And Y3 < 400 Then Y3:+6 'moves computer paddle down. keeps paddle center. If Y -36 < Y3 And Y3 > 0 Then Y3:-6 'moves computer paddle up. keeps paddle center. 'alpha debug (not relevent to the game) If KeyDown(Key_Space) D1=6 If KeyDown(Key_1) D1=1 If KeyDown(Key_0) D1=0 If KeyDown(Key_2) D1=2 If KeyDown(Key_3) D1=3 If KeyDown(Key_4) D1=4 If KeyDown(Key_5) D1=5 'back to game If D1=6 Then B=0 'puts ball reset back to 0 or OFF If D1= 0 X:-3 'ball moves left If D1= 1 X:-3 Y:+7 'ball moves left and down If D1= 2 X:-3 Y:-7 'ball moves left and up If D1= 3 X:+3 'ball moves right If D1= 4 X:+3 Y:+7 'ball moves right and down If D1= 5 X:+3 Y:-7 'ball moves right and up If D1= 6 Then X=320 ; Y=240 'ball reset (ball is in center of screen) If Y >= 472 And D1=1 Then D1=2 'ball bounces back up traveling left If Y >= 472 And D1=4 Then D1=5 'ball bounces back up traveling right If Y <= 0 And D1=2 Then D1=1 'ball bounces back down traveling left If Y <= 0 And D1=5 Then D1=4 'ball bounces back down traveling right If X <= 5 And Y - Y2 <= 80 And Y - Y2 > 40 Then D1 = 4 'player hits bottom of paddle If X <= 5 And Y - Y2 <= 40 And Y - Y2 > 20 Then D1 = 3 'player hits middle of paddle If X <= 5 And Y - Y2 <= 20 And Y - Y2 > -8 Then D1 = 5 'player hits top of paddle If X >= 627 And Y - Y3 <= 80 And Y - Y2 > 40 Then D1 = 1 'computer hits with bottom of paddle If X >= 627 And Y - Y3 <= 40 And Y - Y2 > 20 Then D1 = 0 'computer hits with middle of paddle If X >= 627 And Y - Y3 <= 20 And Y - Y2 > -8 Then D1 = 2 'computer hits with top of paddle If KeyDown(key_down) And y2<400 Then Y2:+5 'center paddle moves down If KeyDown(key_up) And y2>0 Then Y2:-5 'center paddle moves up If X > 640 Or X < -8 Then B = 1 Flip;Cls 'flip draws the action cls clears the screen so the new action can be drawn Wend |
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| try using a codebox like this {codebox} code here {/codebox} except replace {} with [] so here is your code in a codebox: as for your problem um Ill have to look over it. just a minute I honestly can't find a problem. nice pong game though |
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| Press 0 or 3 (to make the ball go left or right) and eventually the ball with go through one of the paddles. |
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| Seems to be these lines to me. You are checking the computers position (Y3). Each line you start with Y - Y3 <=80 etc. but then compare it with the players (Y - Y2) position. I changed (all the Y2 to Y3) and it seems to work okay for me! Unless you keep your hand down on say the "3" key - in which case of course it will go through the paddle. |
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| My first guess is that the ball is moving further in one step than the width of the paddle and thus jumps from one side to the other - a typical collision detection issue. ? |
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| The step size (x) of the ball is either -3, 0 or 3. Both paddle sizes are 5 in width - so the ball moving further than the paddle width is not the issue. I thought the same thing initially. I even slowed the all right down to -1, 0 or 1 and it still happend. It took me a while to notice the lines: If X >= 627 And Y - Y3 <= 80 And Y - Y2 > 40 Then D1 = 1 'computer hits with bottom of paddle Y = Ball Position Y X = Ball Position X Y3 = Top Paddle Position for Computer Y2 = Top Paddle Position for Player So in the above line X>=627 we are checking right side of screen (computer) for a collision, but then using Y2 (Humans Paddle) as part of the collision detection which of course is not correct. As far as I can see, the human paddle collision code is correct, the ball was only ever passing through the computers paddle. I'm still new enough to have not experimented with Images & Image Collision - if the ball and paddle images were Images, you could just use the pre-written image collision functions to do all this for you? BTW, this error is one I also commonly make - happens when you use lots of short X, Y variable names. Maybe if you use: ballX, BallY for the ball playerY for the players paddle computerY for the computers paddle The original code would then change from If X >= 627 And Y - Y3 <= 80 And Y - Y2 > 40 Then D1 = 1 'computer hits with bottom of paddle to If ballX >= 627 and ballY - computerY <=80 and ballY - playerY > 40 then D1 = 1 Which automatically looks wrong, where as Y2 and Y3 is not as noticeable as an error :S Hope that makes sense :) |
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