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C++ & SDLfirst game, Hit detection problem

Schadek (6)
Hello, I recently started to learn C++ and SDL and I am working on a game called "Gun Fight" at the moment. The game is similar to pong in the sense that there are two objects on either side of the screen but in this case they are guns, they can only move vertical. The bullets move horizontal across the screen when shooting at the other gun. Each player has 5 bars of health, one bullet depletes one bar, at the moment when you reach 0 bars nothing happens because I have not programmed it in yet. My trouble is that the hit detection only registers a hit if the gun is also in motion, I can not seem to figure out why (Also there is a bug where the 5 bars of health will sometimes instantly drop after 1 hit, but that is less of a big deal for me)

Hit detection
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 // Hit Detection

   
	if ( bullet2startX + widthb2 > dstX && dstY < bullet2startY && dstY + heightb2 > bullet2startY && shoot2 == true )
	{
		
		if (hwidth3 == 28)
		{
		hwidth3 = 0;

		}
		
		if (hwidth3 == 56)
		{
		hwidth3 = 28;
		}
		
		if (hwidth3 == 84)
		{
		hwidth3 = 56;
		}
		
		if (hwidth3 == 112)
		{
		hwidth3 = 84;
		}

		if (hwidth3 == 140)
		{
		hwidth3 = 112;
		}
		bullet2startX = 1000;
		}

	if ( bullet1startX + widthb1 > dstX2 && dstY2 < bullet1startY && dstY2 + heightb1 > bullet1startY && shoot1 == true )
	{
			
		if (hwidth2 == 28)
		{
		hwidth2 = 0;

		}
		
    	if (hwidth2 == 56)
		{
		hwidth2 = 28;
		}
		
		if (hwidth2 == 84)
		{
		hwidth2 = 56;
		}
		
		if (hwidth2 == 112)
		{
		hwidth2 = 84;
		}

		if (hwidth2 == 140)
		{
		hwidth2 = 112;
		}
		bullet1startX = -1000;
	}


All the variables
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//Integers

// Health Bar
int hwidth = 140;
int hheight = 30;

int hwidth2 = 140;
int hheight2 = 30;
int hwidth3= 140;

int healthx1 = 400;
int healthx2 = 100;
int healthy = 400;


// Gun right
int width = 200;
int height = 200;

int srcX = 0;
int srcY = 0;

int dstX = 530;
int dstY = 150;

// Bullet 1
int widthb1 = 20;
int heightb1 = 20;

int bullet1startX;
int bullet1startY;

// Gun Left
int width2 = 200;
int height2 = 200;

int srcX2 = 0;
int srcY2 = 0;

int dstX2 = -80;
int dstY2 = 150;

// Bullet 2

int widthb2 = 20;
int heightb2 = 20;

int bullet2startX;
int bullet2startY;

int bulletspeed = 1;


Also this is the entire code if you want to take a look at it
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#include <sdl.h>

SDL_Surface *screen = NULL;
SDL_Surface *background = NULL;
SDL_Surface *sprite = NULL;
SDL_Surface *sprite2 = NULL;
SDL_Surface *sprite3 = NULL;
SDL_Surface *sprite4 = NULL;
SDL_Surface *sprite5 = NULL;
SDL_Surface *sprite6 = NULL;
//Integers

// Health Bar
int hwidth = 140;
int hheight = 30;

int hwidth2 = 140;
int hheight2 = 30;
int hwidth3= 140;

int healthx1 = 400;
int healthx2 = 100;
int healthy = 400;


// Gun right
int width = 200;
int height = 200;

int srcX = 0;
int srcY = 0;

int dstX = 530;
int dstY = 150;

// Bullet 1
int widthb1 = 20;
int heightb1 = 20;

int bullet1startX;
int bullet1startY;

// Gun Left
int width2 = 200;
int height2 = 200;

int srcX2 = 0;
int srcY2 = 0;

int dstX2 = -80;
int dstY2 = 150;

// Bullet 2

int widthb2 = 20;
int heightb2 = 20;

int bullet2startX;
int bullet2startY;

int bulletspeed = 1;
// Making an Image for the background
bool run = true;
SDL_Event event;

void surface(int x, int y, SDL_Surface* source, SDL_Surface* destination)
{
SDL_Rect rect;
rect.x = x;
rect.y = y;

SDL_BlitSurface (source, NULL, destination, &rect);

}

void draw_sprite(int srcX,int srcY,
     int dstX,int dstY,
     int width,int height,
     SDL_Surface *source, SDL_Surface *destination)
{
 SDL_Rect src;
 src.x = srcX;
 src.y = srcY;
 src.w = width;
 src.h = height;

 SDL_Rect dst;
 dst.x = dstX;
 dst.y = dstY;
 dst.w = width;
 dst.h = height;

SDL_BlitSurface(source, &src, destination, &dst);
}


int main ( int argc, char* argv[])

{

 SDL_Init(SDL_INIT_EVERYTHING);

 SDL_WM_SetCaption ("Gun Fight",NULL); // Sets caption
 //Load
 screen = SDL_SetVideoMode (640,440,32,SDL_SWSURFACE); //Establishes Screen
 background = SDL_LoadBMP("background.bmp"); // Loads the bmp
 sprite = SDL_LoadBMP("sprite.bmp"); // Loads the bmp
 sprite2 = SDL_LoadBMP("sprite2.bmp"); // Loads the bmp
 sprite3 = SDL_LoadBMP("sprite3.bmp"); // Loads the bmp
 sprite4 = SDL_LoadBMP("sprite4.bmp"); // Loads the bmp
 sprite5 = SDL_LoadBMP("sprite5.bmp"); // Loads the bmp
 sprite6 = SDL_LoadBMP("sprite6.bmp"); // Loads the bmp
 SDL_SetColorKey (sprite,SDL_SRCCOLORKEY,SDL_MapRGB (sprite ->format, 255, 255, 255)); //takes away any of set color
 SDL_SetColorKey (sprite2,SDL_SRCCOLORKEY,SDL_MapRGB (sprite2 ->format, 255, 255, 255)); //takes away any of set color
 SDL_SetColorKey (sprite6,SDL_SRCCOLORKEY,SDL_MapRGB (sprite6 ->format, 255, 255, 255));

 bool keys[323] = {false};
 bool shoot1 = {false};
 bool shoot2 = {false};
 
 while (run)

 {
	if (SDL_PollEvent(&event))
	 {	
		 if (event.type == SDL_QUIT)  
				  {
						  run = false;
				  }
		
		 
		 if(event.type == SDL_KEYDOWN) //If any key is pressed down
			{
			 
			keys[event.key.keysym.sym]	= true;
			
			}
		 if(event.type == SDL_KEYUP)
		 {
			keys[event.key.keysym.sym]	= false;
		 }
	}


// Key presses

// Right Gun
	    if (keys[SDLK_UP])
		{
			dstY -= 1;
		}
		if (keys[SDLK_DOWN])
		{
		dstY += 1;
		}
		
		if ( keys[SDLK_LEFT] & shoot1 == false )
		{
		
		shoot1 = true;
		bullet1startX = dstX;
		bullet1startY = dstY;
		}


// Left Gun
		if ( keys[SDLK_w] )
		{
			dstY2 -= 1;
		}

		if ( keys[SDLK_s] )
		{
			dstY2 += 1;
		}

		if ( keys[SDLK_d] & shoot2 == false )
		{
		
		shoot2 = true;
		bullet2startX = dstX2;
		bullet2startY = dstY2;
		}


// Screen Edges
		if (dstY < 0)
		{
			dstY = 0;
		}

		if (dstY > 360)
		{
			dstY = 360;
		}

		if (dstY2 < 0)
		{
			dstY2 = 0;
		}

		if (dstY2 > 360)
		{
			dstY2 = 360;
		}
	

   surface(0,0,background,screen);
   
    if ( shoot1 == true )
   {
	   if ( bullet1startX > 0 - widthb1 )
	   {
		    draw_sprite(srcX,srcY,
			bullet1startX,bullet1startY,
			widthb1,heightb1, 
			sprite4, screen);

			bullet1startX -= bulletspeed;
	   }
	   else
	   {
		shoot1 = false;
		
	   }
   }

	 if ( shoot2 == true )
   {
	   if ( bullet2startX < 640 - widthb1 )
	   {
		    draw_sprite(srcX2,srcY2,
			bullet2startX,bullet2startY,
			widthb2,heightb2, 
			sprite3, screen);

			bullet2startX += bulletspeed;
	   }
	   else
	   {
		shoot2 = false;
		
	   }
   }


   draw_sprite(srcX,srcY,
      healthx1,healthy,
      hwidth3,hheight, 
      sprite5, screen);
   
   draw_sprite(srcX,srcY,
      healthx1,healthy,
      hwidth,hheight, 
      sprite6, screen);

    draw_sprite(srcX,srcY,
      healthx2,healthy,
      hwidth2,hheight2, 
      sprite5, screen);

	 draw_sprite(srcX,srcY,
      healthx2,healthy,
      hwidth,hheight, 
      sprite6, screen);

   draw_sprite(srcX,srcY,
      dstX,dstY,
      width,height, 
      sprite, screen);
  
   draw_sprite(srcX2,srcY2,
      dstX2,dstY2,
      width2,height2, 
      sprite2, screen);
  
  
   // Hit Detection

   
	if ( bullet2startX + widthb2 > dstX && dstY < bullet2startY && dstY + heightb2 > bullet2startY && shoot2 == true )
	{
		
		if (hwidth3 == 28)
		{
		hwidth3 = 0;

		}
		
		if (hwidth3 == 56)
		{
		hwidth3 = 28;
		}
		
		if (hwidth3 == 84)
		{
		hwidth3 = 56;
		}
		
		if (hwidth3 == 112)
		{
		hwidth3 = 84;
		}

		if (hwidth3 == 140)
		{
		hwidth3 = 112;
		}
		bullet2startX = 1000;
		}

	if ( bullet1startX + widthb1 > dstX2 && dstY2 < bullet1startY && dstY2 + heightb1 > bullet1startY && shoot1 == true )
	{
			
		if (hwidth2 == 28)
		{
		hwidth2 = 0;

		}
		
    	if (hwidth2 == 56)
		{
		hwidth2 = 28;
		}
		
		if (hwidth2 == 84)
		{
		hwidth2 = 56;
		}
		
		if (hwidth2 == 112)
		{
		hwidth2 = 84;
		}

		if (hwidth2 == 140)
		{
		hwidth2 = 112;
		}
		bullet1startX = -1000;
	}
	   SDL_Flip (screen);

 }
 SDL_Quit();
 return 0;

}



Thank you guys for any help you can provide!
(sorry for the messy code)

Also -- Screen shot
http://gyazo.com/3d46592f3e526cd9f8aed0e51eb3dd36
-----

-Kyle
Last edited on
ne555 (10692)
You ought to separate the interface. It will make your code clearer and more maintainable.
I meant, if you get hit the health will decrease. But how many hits you can take, or how will you represent it, it is another issue.

dstY < bullet2startY && dstY + heightb2 > bullet2startY That looks wrong.
I don't see in the code that the gun movement will make any difference.
Schadek (6)
ne555 Thank you for your assistance, I am having trouble understanding what you mean by "separating the interface"

Also, representing the hits that you take is done by re-adjusting the size of a bmp picture of a green bar, which you can see under the if statement for hit detection. The green bar lies underneath a black bar with 5 squares cut out, if you look at the screen shot you will see what I mean.

What looks wrong about the hit detection? could you be more specific

And yes, I do not see any code that the gun movement would make a difference, that is why I do not understand it.
Last edited on
ne555 (10692)
I think it should be dstY < bullet2startY && dstY + height > bullet2startY //The bullet is 'inside' the gun You are just checking the bottom (¿or is it the top?) but that simplification don't hurt so much.

About the health bar. At first I thought that that was part of the detection algorithm.
The thing is, ¿how much code you need to change and how hard is it to locate it, if you want to modify the game?
By instance give them 3 life instead of 5. Or using colors to represent the health.
Or no health at all (the one with more hits in a period wins).

For all that the detection shouldn't be updated. But that is the place where you control everything.
Schadek (6)
Yes I realize the way I am doing it is not even close to efficient, and I can actually locate everything in the game right now, I am sure in a few months I will have trouble remembering.

I tried your theory for hit detection and it caused massive bugs, it caused the bullets to randomly detect being hit through out the entire screen

I reverted the changes and stumbled upon another discovery if the left gun is at the top of the screen, than it can be hit without movement, but not the same for the right gun. This makes me think that it is my hit detection which is off and that the moving gun just causes the bullet to cover the entire gun and can hit the miniscule hit detection block
Schadek (6)
Bump, need to finish this game before tuesday for my computer prog class.
Schadek (6)
I have decided that the Hit Detection box was exactly the size of the bullet, making it nearly impossible to hit the gun unless the gun was in motion or it was a perfect shot. Also, ne555 was right when he was telling me that the hit detection was wrong, but his fixes caused it to bug out because the < > signs were also wrong for the left gun / bullet comming from the right gun. I was woundering where the x and y coords are based from on the picture I.E is it the upper right, left, bottom? etc. Thanks!
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