SDL Phantom Blitting

/*
  lesson5.cpp
  Cone3D GFX with SDL lesson 5.
  Made by Marius Andra 2002
  http://cone3d.gamedev.net

  You can use the code for anything you like.
  Even in a commercial project.
  But please let me know where it ends up.
  I''m just curious. That''s all.
*/

#include <stdio.h>
#include <stdlib.h>
#include <stdarg.h>
#include <string.h>
#include <time.h>

#include "SDL.h"

#include "font.h"

// These two variables contain the dimensions of the playfield

int rows;
int cols;

SDL_Surface *screen;   // The screen surface

SDL_Surface *balls[10];// The ball images

SDLFont *font1;        // 2 fonts

SDLFont *font2;

char *playf;           // The playfield itself


// The default width and height of the screen

int scrwidth=640, scrheight=480;
int centx=0,centy=0;   // Used to center the grid nicely onto the screen


int bls=4;             // Number of differently colored balls


int bla=0;             // Used with the mouse...


int score=0;           // The current score


// This function draws a surface onto the screen

void DrawIMG(SDL_Surface *img, int x, int y)
{
  SDL_Rect dest;
  dest.x = x;
  dest.y = y;
  SDL_BlitSurface(img, NULL, screen, &dest);
}

// This swaps two type char variables

void swap(char &r1, char &r2)
{
  char temp=r1;
  r1=r2;
  r2=temp;
}

// Returns the color of a ball in the playfield.

inline char &grid(int a, int b)
{
  return playf[a*cols+b];
}

// This function makes balls fall down and rows move left.

void collapse()
{
  // Make balls fall down

  int to=-1;
  for(int j=0;j<cols;j++)
  {
    to=-1;
    for(int i=rows-1;i>=0;i--)
    {
      if(to==-1 && grid(i,j)==-1) {to=i;}
      else if(to!=-1 && grid(i,j)!=-1) {swap(grid(i,j),grid(to,j)); to--;}
    }
  }
  
  // Move rows to the left

  to=-1;
  {
    for(int j=0;j<cols;j++)
    {
  	  if(to==-1 && grid(rows-1,j)==-1)
      {
        to=j;
      } else if(to!=-1 && grid(rows-1,j)!=-1) {
        for(int i=0;i<rows;i++)
        {
          grid(i,to) = grid(i,j);
        }
  	    to++;
      }
    }
	
    {
      if(to!=-1)
      {
        for(int j=to;j<cols;j++)
        {
          for(int i=0;i<rows;i++)
          {
            grid(i,j)=-1;
          }
   	    }
      }
    }
  }
}

// This is a recursive function that clears a bunch of balls.

// It uses the flood fill algorithm

int pick(int i, int j, int a)
{
  int sum=1;
  grid(i,j)=-1;
  if(i != 0 && grid(i-1,j)==a) sum+=pick(i-1,j,a);
  if(j != 0 && grid(i,j-1)==a) sum+=pick(i,j-1,a);
  if(i<rows-1 && grid(i+1,j) == a) sum+=pick(i+1,j,a);
  if(j<cols-1 && grid(i,j+1) == a) sum+=pick(i,j+1,a);
  return sum;
}

// This function checks whether one ball is connected to an other

int bunch(int i,int j)
{
  int a = grid(i,j);
  if(i!=0 && grid(i-1,j) == a) return 1;
  if(j!=0 && grid(i,j-1) == a) return 1;
  if(i<rows-1 && grid(i+1,j) == a) return 1;
  if(j<cols-1 && grid(i,j+1) == a) return 1;
  return 0;
}

// Draw the screen

void DrawScene()
{
  //SDL_ShowCursor(0);                    // Hide the mouse cursor

  SDL_FillRect(screen,NULL,0x000000);   // Clear the entire screen with black


  // Draw the balls

  for(int i=0;i<rows;i++)
  {
    for(int j=0;j<cols;j++)
    {
      if(grid(i,j)!=-1) DrawIMG(balls[grid(i,j)],j*45+centx,i*45+centy);
    }
  }

  // Draw some info and the score

  drawString(screen,font1,1,scrheight-16,"SPACE restarts, gray + and - change the nr of balls (%d). Score: %d",bls,score);

  // Draw the webspace url to the bottom-right of the screen

  drawString(screen,font2,scrwidth-stringWidth(font2,"http://cone3d.gamedev.net"),

                                        scrheight-16,"http://cone3d.gamedev.net");

  SDL_Flip(screen);        // Flip the buffers

  //SDL_ShowCursor(1);       // Show the cursor again

}

// This function resets the entire grid by adding random balls to it

void newgame()
{
  // Reset the score

  score=0;

  // Fill the grid with random balls

  for(int i=0;i<rows;i++)
  {
    for(int j=0;j<cols;j++)
    {
      grid(i,j) = rand()%bls;
    }
  }

  // Redraw the screen

  DrawScene();
}

// This is our main function

int main(int argc, char *argv[])
{
  srand(time(NULL));    // We initalize the random number generator


  // Depending on the command line arguments given to this program,

  // we change the screen resolution.

  if(argc>1 && strcmp(argv[1],"640")==0) {scrwidth=640;scrheight=480;}
  if(argc>1 && strcmp(argv[1],"800")==0) {scrwidth=800;scrheight=600;}
  if(argc>1 && strcmp(argv[1],"1024")==0) {scrwidth=1024;scrheight=768;}
  if(argc>1 && strcmp(argv[1],"1152")==0) {scrwidth=1152;scrheight=864;}
  if(argc>1 && strcmp(argv[1],"1280")==0) {scrwidth=1280;scrheight=960;}
  if(argc>1 && strcmp(argv[1],"1600")==0) {scrwidth=1600;scrheight=1200;}

  // Initalize SDL

  if ( SDL_Init(SDL_INIT_AUDIO|SDL_INIT_VIDEO) < 0 )
  {
    printf("Unable to init SDL: %s\n", SDL_GetError());
    exit(1);
  }
  atexit(SDL_Quit);

  // We load in a random ball image as the icon for this program

  char tempstring[100];
  sprintf(tempstring,"data/balls/%d.bmp",rand()%9+1);
  SDL_WM_SetIcon(SDL_LoadBMP(tempstring),NULL);

  // Initalize the video mode

  screen=SDL_SetVideoMode(scrwidth,scrheight,32,SDL_HWSURFACE|SDL_HWPALETTE);
  if ( screen == NULL )
  {
    printf("Unable to set %dx%d video: %s\n", scrwidth, scrheight, SDL_GetError());
    exit(1);
  }

  // Load in the fonts

  font1 = initFont("data/font1");
  font2 = initFont("data/font2",1,1,0);

  // Load in all the balls

  for(int a=1;a<10;a++)
  {
    char temp[100];
    sprintf(temp,"data/balls/%d.bmp",a);
    balls[a-1]=SDL_LoadBMP(temp);
  }

  // Calculate how much balls fit on the screen with the current

  // screen resolution

  rows=(scrheight-16)/45;
  cols=(scrwidth)/45;

  // Calculate how much must the balls be movedso that they would be centered.

  centx = (scrwidth-cols*45)/2;
  centy = (scrheight-16-rows*45)/2;

  // Allocate space for the playfield

  playf = new char[rows*cols];

  // Reset the score and generate the playfield

  newgame();

  // Loop a bit

  int done=0;
  while(done == 0)
  {
    DrawScene();
    SDL_Delay(30);
    SDL_Event event;

    while ( SDL_PollEvent(&event) )
    {
      // If someone closes the prorgam, then quit

      if ( event.type == SDL_QUIT )  {  done = 1;  }

      if ( event.type == SDL_KEYDOWN )
      {
        // If someone presses ESC, then quit

        if ( event.key.keysym.sym == SDLK_ESCAPE ) { done = 1; }
        // Space restarts the game

        if ( event.key.keysym.sym == SDLK_SPACE ) { newgame(); }
        // The gray keypad + increases the nr. of different balls

        if ( event.key.keysym.sym == SDLK_KP_PLUS ) { if(bls<9) {bls++;newgame();} }
        // The gray keypad - decreases the nr. of different balls

        if ( event.key.keysym.sym == SDLK_KP_MINUS ) { if(bls>3) {bls--;newgame(); } }
      }
    }

    int x,y;     // Used to hold the mouse coordinates

    int x2,y2;   // Used to hold the ball coordinates

    float x3,y3; // Used to temporarily hold the ball coordinates

    SDL_GetMouseState(&x, &y);    // Get the mouse coords

    x3=(((float)(x-centx))/45);   // Get the ball coords

    y3=(((float)(y-centy))/45);
    if(x3<0 || y3<0) continue;    // If they are negative, restart the loop

    else {x2=(int)x3;y2=(int)y3;} // else store them as ints


    // If the mouse button is released, make bla equal 1

    if(!SDL_GetMouseState(NULL, NULL)&SDL_BUTTON(1))
    {
      bla=1;
    }

    // If the mouse button was released the previous frame and is now

    // held down, then ...

    if(SDL_GetMouseState(NULL, NULL)&SDL_BUTTON(1) && bla==1)
    {
      // Make bla equal zero so that we could get here only if we release

      // the mouse button and then click it again.

      bla=0;
      // Investigate the clicked ball

      if(x2>=0 && y2>=0 && x2<cols && y2<rows && grid(y2,x2) != -1 && bunch(y2,x2))
      {
        // If it really is clickable then get rid of the balls

        int a=pick(y2,x2,grid(y2,x2));
        // Increase the score by the (removed balls-2)^2

        score+=(a-2)*(a-2);
        // Make the balls fall down

        collapse();
        // And update the screen

        
      }
    }
  }

  // Let''s clean up...

  freeFont(font1);
  freeFont(font2);

  return 0;
}