Graal Forums - Collision check script error

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Collision check script error

I'm having a problem constructing collision checks for a replica of the classic Pong game.
I'll post all of the code before I explain the problem:

PHP Code:


		
			
//#CLIENTSIDE



const BALL_SPEED = 6;



function onWeaponFired(){



  this.game_active = !this.game_active;



  if(this.game_active){

    onInitiatePong();

  }

  else {

    onClosePong();

  }

}



function onInitiatePong(){



  // Scaling of game screen and objects

  temp.court_width = 500;

  temp.court_height = 350;

  temp.paddle_width = 20;

  temp.paddle_height = 100;

  temp.ball_width = 16;

  temp.ball_height = 16;



  // Black background

  showPoly(1000, {(screenwidth/2)-(temp.court_width/2), (screenheight/2)-(temp.court_height/2),

                  (screenwidth/2)+(temp.court_width/2), (screenheight/2)-(temp.court_height/2),

                  (screenwidth/2)+(temp.court_width/2), (screenheight/2)+(temp.court_height/2),

                  (screenwidth/2)-(temp.court_width/2), (screenheight/2)+(temp.court_height/2)});

  changeImgColors(1000, 0, 0, 0, 1);

  changeImgVis(1000, 5);

  

  // Left white paddle

  showPoly(1001, {(screenwidth/2)-(temp.court_width/2)+10, (screenheight/2)-(temp.paddle_height/2),

                  (screenwidth/2)-(temp.court_width/2)+10+temp.paddle_width, (screenheight/2)-(temp.paddle_height/2),

                  (screenwidth/2)-(temp.court_width/2)+10+temp.paddle_width, (screenheight/2)+(temp.paddle_height/2),

                  (screenwidth/2)-(temp.court_width/2)+10, (screenheight/2)+(temp.paddle_height/2)});

  changeImgColors(1001, 1, 1, 1, 1);

  changeImgVis(1001, 6);

  

  // Right white paddle

  showPoly(1002, {(screenwidth/2)+(temp.court_width/2)-10, (screenheight/2)-(temp.paddle_height/2),

                  (screenwidth/2)+(temp.court_width/2)-10-temp.paddle_width, (screenheight/2)-(temp.paddle_height/2),

                  (screenwidth/2)+(temp.court_width/2)-10-temp.paddle_width, (screenheight/2)+(temp.paddle_height/2),

                  (screenwidth/2)+(temp.court_width/2)-10, (screenheight/2)+(temp.paddle_height/2)});

  changeImgColors(1002, 1, 1, 1, 1);

  changeImgVis(1002, 6);

  

  // Central white divider

  showPoly(1003, {(screenwidth/2), (screenheight/2)-(temp.court_height/2),

                  (screenwidth/2), (screenheight/2)+(temp.court_height/2)-1});

  changeImgColors(1003, 1, 1, 1, 1);

  changeImgVis(1003, 6);

  

  // Centre-starting ball

  showPoly(1004, {(screenwidth/2)-(temp.ball_width/2), (screenheight/2)-(temp.ball_height/2),

                  (screenwidth/2)+(temp.ball_width/2), (screenheight/2)-(temp.ball_height/2),

                  (screenwidth/2)+(temp.ball_width/2), (screenheight/2)+(temp.ball_height/2),

                  (screenwidth/2)-(temp.ball_width/2), (screenheight/2)+(temp.ball_height/2)});

  changeImgColors(1004, 1, 1, 1, 1);

  changeImgVis(1004, 7);

  

  scheduleEvent(0.5, "StartPong", NULL);

}



function onStartPong(){



  temp.ball_angle = random(0, 360);

  

  onMoveBall(temp.ball_angle);

}



function onMoveBall(temp.angle){



  cancelEvents("MoveBall");

  

  if(int(temp.angle % 90) == 0){

    temp.angle += random(-10, 10);

  }

  

  // Ball collision detection and angle adjustment

  for(temp.iy = 1; temp.iy <= 7; temp.iy += 2){

    if(findImg(1004).polygon[temp.iy] - cos(degtorad(temp.angle)) * BALL_SPEED < findImg(1000).polygon[1] ||

      findImg(1004).polygon[temp.iy] - cos(degtorad(temp.angle)) * BALL_SPEED > findImg(1000).polygon[7]){

      temp.angle = 180 - temp.angle;

    }

    // First collision check

    if(findImg(1004).polygon[temp.iy-1] + sin(degtorad(temp.angle)) * BALL_SPEED in |findImg(1001).polygon[0], findImg(1001).polygon[2]|){

      if(findImg(1004).polygon[temp.iy] - cos(degtorad(temp.angle)) * BALL_SPEED in |findImg(1001).polygon[7]-10, findImg(1001).polygon[7]| ||

        findImg(1004).polygon[temp.iy] - cos(degtorad(temp.angle)) * BALL_SPEED in |findImg(1001).polygon[1], findImg(1001).polygon[1]+10|){

        temp.angle = 180 - temp.angle;

      }

      // Second collision check

      // MY PROBLEM IS THE LINE BELOW

      else if(findImg(1004).polygon[temp.iy] - cos(degtorad(temp.angle)) * BALL_SPEED in |findImg(1002).polygon[7]-10, findImg(1002).polygon[7]| ||

        findImg(1004).polygon[temp.iy] - cos(degtorad(temp.angle)) * BALL_SPEED in |findImg(1002).polygon[1], findImg(1002).polygon[1]+10|){

        temp.angle = 180 - temp.angle;

      }

    }

  }

  

  // Moving the ball along angle

  for(temp.bx = 0; temp.bx <= 6; temp.bx += 2){

    findImg(1004).polygon[temp.bx] += sin(degtorad(temp.angle)) * BALL_SPEED;

  }

  for(temp.by = 1; temp.by <= 7; temp.by += 2){

    findImg(1004).polygon[temp.by] -= cos(degtorad(temp.angle)) * BALL_SPEED;

  }

  

  showText(1005, findImg(1004).polygon[0], findImg(1004).polygon[1] - 20, "Arial", "c", temp.angle);

  changeImgVis(1005, 7);

  

  if(this.game_active){

    scheduleEvent(0.05, "MoveBall", temp.angle);

  }

}



function onClosePong(){



  hideImgs(1000, 1004);

}

If you scroll about halfway down, you'll get to the collision checks under the onMoveBall function, you'll see where I've highlighted my problem.
When the script is as it is in this post, the first collision check works fine but the second check does not, and RC gives no error messages about the script.
However, if you add a line before the second collision check such as this:

PHP Code:


		
			
player.chat = "blah";

RC then gives an error message about the line below, causing the whole collision detection to stop working.
Thanks.

Those checks are a little too complicated for a simple pong game, which is the first thing that stands out to me.

Well it's pretty obvious that if you place a player.chat = "bla"; before an else if that your code will break:

PHP Code:


		
			
if (bla) {

}
player.chat = "hi";
else if (bla2) {

}

This will obviously not work... so I don't think that it has anything to do with your syntax really lol

Quote:

Originally Posted by Pelikano (Post 1682411)

Well it's pretty obvious that if you place a player.chat = "bla"; before an else if that your code will break:

PHP Code:


		
			
if (bla) {



}

player.chat = "hi";

else if (bla2) {



}

This will obviously not work... so I don't think that it has anything to do with your syntax really lol

Ah yes, you're right.
I wasn't thinking straight when doing this it seems. Guess I was too frustrated trying to get my second collision check to work. Thanks.

Hezzy, can you suggest a simpler alternative to what I currently have?

Why are you storing angles as degrees and then repeatedly converting them to radians? Why not just store them as radians?

Quote:

Originally Posted by iBeatz (Post 1682412)

Well, it's just pong. You can just do an axis-aligned bounding box check, or rectangle intersection. You don't have to use any trig or angle work, just some basic math.

Actually from what I remember, using angles just made pong much more complicated to code. Use vectors instead.

You can clean up your code quite a bit by:

1. Reducing the amount of math you do in an if statement.
2. temp.img = findimg(1004); then instead of using findimg(1004) just use your variable reference instead.
3. Same idea as 2 but you do the same calculation numerous times, do it once and store the value in a variable for re-use it instead.

Separate your presentation code from the game logic and you will simplify things immensely. You'll have code that's easier to understand, easier to change later, and is less prone to errors.

For example, something like:

PHP Code:


		
			
if (RIGHT_WALL_X - ball.pos.x < ball.radius) {

  // we have a collision on the right wall!!

}

is much easier to manage and understand than your code (which I'm only assuming is doing something similar to what's above):

PHP Code:


		
			
if(findImg(1004).polygon[temp.iy] - cos(degtorad(temp.angle)) * BALL_SPEED < findImg(1000).polygon[1] || 

      findImg(1004).polygon[temp.iy] - cos(degtorad(temp.angle)) * BALL_SPEED > findImg(1000).polygon[7]){ 

      temp.angle = 180 - temp.angle; 

    }

In your game loop, you would have something like:

PHP Code:


		
			
function gameLoop() {

  updateGame(); // updates the model (check for collisions, move ball, etc)

  renderGame(); // draws the model in its current state



  // .. loop endlessly

}

Use simple units for the model (for example, a ball with a width of 1 unit instead of 16 pixels) and then when you are drawing the game, just convert the units to pixels (or tiles, or whatever). This would also allow you to change the way you render the game without having to mess with the game logic at all.

Also, I would use vectors for something like this, too.