SDL collision bounds problem

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SDL collision bounds problem

SDL collision bounds problem

adam2016 (1529)

hey guys I seem to be having a problem with the bounds checking/collision detection in my game,

when the ball is on the platform and collides with the left most bound the ball indeed hits the "wall" and bounces off it but when the ball is in the air it seems to break this condition and moves past the "wall" or bounds

here is a video displaying what is happening below

https://youtu.be/1X-hrsIwzXs

I'll include the full code below


#include <iostream>
#include <SDL2/SDL.h>
#include <SDL2/SDL_image.h>

using namespace std;

const int HEIGHT = 500;
const int WIDTH = 800;

SDL_Renderer* renderer;
SDL_Window* window;
SDL_Event event;
bool ballDown,ballUp;
bool ballLeft,ballRight;
bool platformOne,platformTwo;
bool ballDropped;
bool ballFalling;
bool jumping;
bool jumpDown;

// ball
SDL_Texture* ballTexture;
SDL_Surface* ballSurface;
SDL_Rect* ballSrcRect;
SDL_Rect* ballDstRect;

// platform
SDL_Texture* platformTexture;
SDL_Surface* platformSurface;
SDL_Rect* platformSrcRect;
SDL_Rect* platformDstRect;

// platformTwo
SDL_Texture* platformTextureTwo;
SDL_Rect* platformTwoSrcRect;
SDL_Rect* platformTwoDstRect;

void initGame(){

   if(SDL_Init(SDL_INIT_EVERYTHING) < 0){

      cout << "failed to init" << endl;
   }
   if(IMG_Init(IMG_INIT_PNG) < 0){

     cout << "failed to init image" << endl;
   }

   window = SDL_CreateWindow("platforms",SDL_WINDOWPOS_CENTERED,SDL_WINDOWPOS_CENTERED,WIDTH,HEIGHT,SDL_WINDOW_RESIZABLE);
   renderer = SDL_CreateRenderer(window,-1,0);
   SDL_SetRenderDrawColor(renderer,255,255,255,255);
   ballDown = true;
   ballUp = false;
   ballLeft = false;
   ballRight = false;

   ballDropped = false;
   ballFalling = false;

   jumping = false;
   jumpDown = false;

   platformOne = true;
   platformTwo = false;

   ballSrcRect = new SDL_Rect;
   ballDstRect = new SDL_Rect;

   platformDstRect = new SDL_Rect;
   platformSrcRect = new SDL_Rect;

   platformTwoDstRect = new SDL_Rect;
   platformTwoDstRect = new SDL_Rect;

   ballSurface = IMG_Load("bb.png");
   ballTexture = SDL_CreateTextureFromSurface(renderer,ballSurface);

   platformSurface = IMG_Load("platform.png");
   platformTexture = SDL_CreateTextureFromSurface(renderer,platformSurface);

   platformTextureTwo = SDL_CreateTextureFromSurface(renderer,platformSurface);

   ballDstRect->x = 30;
   ballDstRect->y = 10;
   ballDstRect->h =70;
   ballDstRect->w = 70;

   platformDstRect->x = 0;
   platformDstRect->y = 400;
   platformDstRect->w = 300;
   platformDstRect->h = 60;

   platformTwoDstRect->x = 470;
   platformTwoDstRect->y = 350;
   platformTwoDstRect->w = 300;
   platformTwoDstRect->h = 60;

}

bool collision(){

  cout << "collision" << endl;
  if(ballDstRect->y + ballDstRect->h >= platformDstRect->y && platformOne){

    cout << "colission platform one" << endl;
    ballDown = false;

    return true;
  }
  if(ballDstRect->y + ballDstRect->h >= platformTwoDstRect->y && platformTwo){

   cout << "colide platform 2" << endl;
     ballDown = false;

    return true;
  }
  cout << "return collision falsr" << endl;
  return false;

}

void move();
void renderGame();

// drop ball allow no user input
void ballDrop(){


  while(true){

     move();
     renderGame();
     SDL_Delay(1);
     //cout << "while" << endl;

     if(collision()){

        //cout << "collision£££££££££" << endl;
        break;
     }
  }

  ballDropped = true;
  return;

}

bool collisionBounds(){

   if(ballDstRect->x <= 0){

    //cout << "here" << endl;
    ballLeft = false;
    ballDstRect->x += 2;
    return true;
  }
  return false;
}

void move(){

   // cout << "MOVE!!!!!!!!!!!!!!!!!!!!" << endl;

   if(ballDown){

      ballDstRect->y++;
   }
   if(ballRight){

     ballDstRect->x++;
   }
   if(ballLeft){

     ballDstRect->x--;
   }
   if(jumpDown){
      //cout << "JUMP DOWN" << endl;
     ballDstRect->y++;
   }

   // check which platform

//   cout << "ball x : " << ballDstRect->x << endl;
//   cout << "ball x + w :" << ballDstRect->x + ballDstRect->w << endl;
//   cout << "platform x + w : " << platformDstRect->x + platformDstRect->w << endl;
//   cout << "platformTwo x : " << platformTwoDstRect->x << endl;
//   cout << "platformRwo x + w : " << platformTwoDstRect->x + platformTwoDstRect->w << endl;




   if((ballDstRect->x <= (platformDstRect->x + platformDstRect->w)) &&
      (ballDstRect->x >= platformDstRect->x)){

      //cout << "PLATFORM ONE" << endl;
      //cout << "ball x + w :" << ballDstRect->x + ballDstRect->w << endl;
      //cout << "platform x + w : " << platformDstRect->x + platformDstRect->w << endl;
      platformOne = true;
      platformTwo = false;
      return;
   }

   //cout << "TEST TEST test" << endl;

    if(!jumping)
        //cout << "!!!! JUMPING" << endl;

   if((ballDstRect->x + ballDstRect->w < platformTwoDstRect->x) && (ballDstRect->x >= platformDstRect->x +
    platformDstRect->w) && (!jumping) ){

        //cout << "OFF PLATFORM" << endl;
        ballDown = true;
        ballFalling = true;
        platformOne = false;
        platformTwo = false;
        return;
    }

   if(ballDstRect->x >= (platformDstRect->x + platformDstRect->w)){

      //cout << "PLATFORM TWO" << endl;
      platformOne = false;
      platformTwo = true;
      return;
   }
}

void renderGame(){

  SDL_RenderClear(renderer);

  SDL_RenderCopy(renderer,ballTexture,NULL,ballDstRect);
  SDL_RenderCopy(renderer,platformTexture,NULL,platformDstRect);
  SDL_RenderCopy(renderer,platformTextureTwo,NULL,platformTwoDstRect);

  SDL_RenderPresent(renderer);
}

void falling(bool &quit){

  if(ballFalling){

    for(int i = ballDstRect->x; i < HEIGHT+10; i++){


        ballDstRect->y++;
        renderGame();
        SDL_Delay(1);

    }
      quit = true;
  }

}


void jump(){

    ballDstRect->y-=2;
}


int SDL_main(int argc,char* argv[])
{

    initGame();

    bool quit = false;


    while(!quit){

        SDL_PollEvent(&event);

        if(!ballDropped){

            ballDrop();
        }

        if(event.type == SDL_QUIT){
            //cout << "quit" << endl;
            quit = true;
        }
        if(event.type == SDL_KEYDOWN){

            switch(event.key.keysym.sym){

        case SDLK_RIGHT:
            ballLeft = false;
            ballRight = true;
            break;
        case SDLK_LEFT:
            ballRight = false;
            ballLeft = true;
            break;
        case SDLK_UP:
            jump();
            renderGame();
            //cout << "UP" << endl;
            jumping = true;
            jumpDown = true;
            break;

            }
            if(!collision() || !collisionBounds()){
            move();
            }
            falling(quit);
        }
        if(event.type == SDL_KEYUP && jumpDown){

            switch(event.key.keysym.sym){

          case SDLK_UP:
            ballDrop();
            jumpDown = false;
            jumping = false;
            //cout << "down" << endl;
            break;
            }
            if(!collision() || !collisionBounds()){
            move();
            }
            falling(quit);
        }

        SDL_Delay(1);
        renderGame();
    }
}

Peter87 (11179)

The || and && operators only evaluates the second operand expression if it is necessary in order to decide the result.

This causes problems in the following code.

1
2
3

if (!collision() || !collisionBounds()) {
	move();
}

If !collision() returns true, meaning the ball does not collide with any of the platforms, then it will not call the collisionBounds() because it already knows that the result of the || is going to be true.

Last edited on

adam2016 (1529)

Hi Peter,

I tried removing the logical or and used logical and, but now the ball doesn't seem to move at all when I use &&

**edit

I removed the || and just checked for collisionBounds and called the collision function in inside this block,seemed to kind of do the job I mean kind of because it's still very buggy,I will post a new video showing what I mean by buggy,thanks Peter

if(!collisionBounds()){
            move();
            collision();
            }

Last edited on

jonnin (11348)

what is the condition under which you want it to move() ?
say that in english.
then turn that english into the expression you want.
I can take a guess, but you need to do this for yourself -- its one of the 3 or 4 techniques that I use when dealing with conditions. This method sometimes leads to suboptimal logic but its part of the (get it working, then make it fast) approach. This is the get it working piece, you can tune it after.

given the nature of this code, you may discover that one or both of your functions are not doing exactly what you expected. Collision by the way has some typos. like falsr and 2 distinct prints that maybe should say things the same way (?).

if everything is doing exactly what you wanted, and you are sure of it, you can test the short circuit problem manually:
bool col = !collision();
cout << col
col = !collisionBounds();
cout << col
see which of those is messing you up, then print what it did inside the functions, see what you got vs what you expected...

Last edited on

adam2016 (1529)

https://youtu.be/Mg15gXeUFZ8

here is the video illustrating the bugs,

Jonnin I would like the ball to move when there is no bounds collision(against the right wall) the ball should be able to move under any other conditions,well to add on to that when I noticed when I jump sometimes the ball keeps on moving right or left without me even pushing the right or left key,so the ball should not move horizontally in either direction when the key is not pressed but should move when that key is pressed be it jumping or not.

given the nature of this code, you may discover that one or both of your functions are not doing exactly what you expected. Collision by the way has some typos. like falsr and 2 distinct prints that maybe should say things the same way (?).

I removed the call to collision and the code seems to be the exact same thing,starting to think maybe the collision function isn't needed in the first place?

see which of those is messing you up, then print what it did inside the functions, see what you got vs what you expected...

good iea never thought about that

Last edited on

adam2016 (1529)

looks like I was wrong the collision function was actually vital,seems like I have got past the bug for now(fingers crossed)

I never thought of it directly like that before but yes that is actually very good advice,would you advise to write it on a piece of paper etc then try to implement it with code?

constructive criticism is always welcome if anybody wants to point out any flaws in my code( and yes I know one flaw is don't free the memory/resources used I still need to implement a function that does this)

thanks


bool collision(){

  if(ballDstRect->y + ballDstRect->h >= platformDstRect->y && platformOne){

    cout << "colission platform one" << endl;
    ballDown = false;
    ballDstRect->y = platformDstRect->y - ballDstRect->h; // line that fixed the bug

    return true;
  }
  if(ballDstRect->y + ballDstRect->h >= platformTwoDstRect->y && platformTwo){

   cout << "colide platform 2" << endl;
     ballDown = false;
     ballDstRect->y = platformTwoDstRect->y - ballDstRect->h; // also fixed the bug

    return true;
  }
  cout << "return collision false" << endl;
  return false;

}

jonnin (11348)

I never thought of it directly like that before but yes that is actually very good advice,would you advise to write it on a piece of paper etc then try to implement it with code?

I hesitate to comment. If the logic is like 5 conditions, you need to write it down and go over it a bit. If its 2 conditions like you have, you can do it in your head maybe, or maybe writing it will help you, that depends on how your mind works -- I can do a fair bit in my head before going to paper, but that has burned me plenty of times too. I tend to give it one or 2 goes in my head and then write if it still is broken, or directly to writing it down if its more than 2 or 3 basic conditions. But everyone is different on what they need here. In your case the logic was fine, but the functions had a bug -- which I suspected, given the simplicity of the logical test.

if that text is not just to debug the thing, you might want to clean it up, its inconsistent and typos. If its for debug, whatever.

adam2016 (1529)

Thanks Jonnin :)

yes the text is just for debugging I will have to replace them with some comments when it's finished

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