// this function tests if the ball has hit a block or the paddle
// if so, the ball is bounced and the block is removed from 
// the playfield note: very cheesy collision algorithm :)

// first test for ball block collisions

// the algorithm basically tests the ball against each 
// block's bounding box this is inefficient, but easy to 
// implement, later we'll see a better way

int x1 = BLOCK_ORIGIN_X, // current rendering position
    y1 = BLOCK_ORIGIN_Y; 

int ball_cx = ball_x+(BALL_SIZE/2),  // computer center of ball
    ball_cy = ball_y+(BALL_SIZE/2);

// test of the ball has hit the paddle
if (ball_y > (SCREEN_HEIGHT/2) && ball_dy > 0)
   {
   // extract leading edge of ball
   int x = ball_x+(BALL_SIZE/2);
   int y = ball_y+(BALL_SIZE/2);

   // test for collision with paddle
   if ((x >= paddle_x && x <= paddle_x+PADDLE_WIDTH) &&
       (y >= paddle_y && y <= paddle_y+PADDLE_HEIGHT))
       {
       // reflect ball
       ball_dy=-ball_dy;

       // push ball out of paddle since it made contact
       ball_y+=ball_dy;

       // add a little english to ball based on motion of paddle
       if (KEY_DOWN(VK_RIGHT))
          ball_dx-=(rand()%3);
       else
       if (KEY_DOWN(VK_LEFT))
          ball_dx+=(rand()%3);
       else
          ball_dx+=(-1+rand()%3);
       
       // test if there are no blocks, if so send a message
       // to game loop to start another level
       if (blocks_hit >= (NUM_BLOCK_ROWS*NUM_BLOCK_COLUMNS))
          {
          game_state = GAME_STATE_START_LEVEL;
          level++;
          } // end if

       // make a little noise
       MessageBeep(MB_OK);

       // return
       return; 

       } // end if

   } // end if

// now scan thru all the blocks and see of ball hit blocks
for (int row=0; row < NUM_BLOCK_ROWS; row++)
    {    
    // reset column position
    x1 = BLOCK_ORIGIN_X;

    // scan this row of blocks
    for (int col=0; col < NUM_BLOCK_COLUMNS; col++)
        {
        // if there is a block here then test it against ball
        if (blocks[row][col]!=0)
           {
           // test ball against bounding box of block
           if ((ball_cx > x1) && (ball_cx < x1+BLOCK_WIDTH) &&     
               (ball_cy > y1) && (ball_cy < y1+BLOCK_HEIGHT))
               {
               // remove the block
               blocks[row][col] = 0; 

               // increment global block counter, so we know 
               // when to start another level up
               blocks_hit++;

               // bounce the ball
               ball_dy=-ball_dy;

               // add a little english
               ball_dx+=(-1+rand()%3);

               // make a little noise
               MessageBeep(MB_OK);

               // add some points
               score+=5*(level+(abs(ball_dx)));

               // that's it -- no more block
               return;

               } // end if  

           } // end if

        // advance column position
        x1+=BLOCK_X_GAP;
        } // end for col

    // advance to next row position
    y1+=BLOCK_Y_GAP;

    } // end for row

} // end Process_Ball

///////////////////////////////////////////////////////////////

int Game_Main(void *parms)
{
// this is the workhorse of your game it will be called
// continuously in real-time this is like main() in C
// all the calls for you game go here!

char buffer[80]; // used to print text

// what state is the game in? 
if (game_state == GAME_STATE_INIT)
    {
    // initialize everything here graphics
    DD_Init(SCREEN_WIDTH, SCREEN_HEIGHT, SCREEN_BPP);

    // seed the random number generator
    // so game is different each play
    srand(Start_Clock());

    // set the paddle position here to the middle bottom
    paddle_x = PADDLE_START_X;
    paddle_y = PADDLE_START_Y;

    // set ball position and velocity
    ball_x = 8+rand()%(SCREEN_WIDTH-16);
    ball_y = BALL_START_Y;
    ball_dx = -4 + rand()%(8+1);
    ball_dy = 6 + rand()%2;

    // transition to start level state
    game_state = GAME_STATE_START_LEVEL;

    } // end if 
////////////////////////////////////////////////////////////////
else
if (game_state == GAME_STATE_START_LEVEL)
    {
    // get a new level ready to run

    // initialize the blocks
    Init_Blocks();

    // reset block counter
    blocks_hit = 0;

    // transition to run state
    game_state = GAME_STATE_RUN;

    } // end if
///////////////////////////////////////////////////////////////
else
if (game_state == GAME_STATE_RUN)
    {
    // start the timing clock
    Start_Clock();

    // clear drawing surface for the next frame of animation
    Draw_Rectangle(0,0,SCREEN_WIDTH-1, SCREEN_HEIGHT-1,200);

    // move the paddle
    if (KEY_DOWN(VK_RIGHT))
       {
       // move paddle to right
       paddle_x+=8;
 
       // make sure paddle doesn't go off screen
       if (paddle_x > (SCREEN_WIDTH-PADDLE_WIDTH))
          paddle_x = SCREEN_WIDTH-PADDLE_WIDTH;

       } // end if
    else
    if (KEY_DOWN(VK_LEFT))
       {
       // move paddle to right
       paddle_x-=8;
 
       // make sure paddle doesn't go off screen
       if (paddle_x < 0)
          paddle_x = 0;

       } // end if

    // draw blocks
    Draw_Blocks();

    // move the ball
    ball_x+=ball_dx;
    ball_y+=ball_dy;

    // keep ball on screen, if the ball hits the edge of 
    // screen then bounce it by reflecting its velocity
    if (ball_x > (SCREEN_WIDTH - BALL_SIZE) || ball_x < 0) 
       {
       // reflect x-axis velocity
       ball_dx=-ball_dx;

       // update position 
       ball_x+=ball_dx;
       } // end if

    // now y-axis
    if (ball_y < 0) 
       {
       // reflect y-axis velocity
       ball_dy=-ball_dy;

       // update position 
       ball_y+=ball_dy;
       } // end if
   else 
   // penalize player for missing the ball
   if (ball_y > (SCREEN_HEIGHT - BALL_SIZE))
       {
       // reflect y-axis velocity
       ball_dy=-ball_dy;

       // update position 
       ball_y+=ball_dy;

       // minus the score
       score-=100;

       } // end if

    // next watch out for ball velocity getting out of hand
    if (ball_dx > 8) ball_dx = 8;
    else
    if (ball_dx < -8) ball_dx = -8;    

    // test if ball hit any blocks or the paddle
    Process_Ball();

    // draw the paddle and shadow
    Draw_Rectangle(paddle_x-8, paddle_y+8, 
                   paddle_x+PADDLE_WIDTH-8, 
                   paddle_y+PADDLE_HEIGHT+8,0);

    Draw_Rectangle(paddle_x, paddle_y, 
                   paddle_x+PADDLE_WIDTH, 
                   paddle_y+PADDLE_HEIGHT,PADDLE_COLOR);

    // draw the ball
    Draw_Rectangle(ball_x-4, ball_y+4, ball_x+BALL_SIZE-4, 
                   ball_y+BALL_SIZE+4, 0);
    Draw_Rectangle(ball_x, ball_y, ball_x+BALL_SIZE, 
                   ball_y+BALL_SIZE, 255);

    // draw the info
    sprintf(buffer,"F R E A K O U T           Score %d             Level %d",score,level);
    Draw_Text_GDI(buffer, 8,SCREEN_HEIGHT-16, 127);
    
    // flip the surfaces
    DD_Flip();

    // sync to 33ish fps
    Wait_Clock(30);

    // check of user is trying to exit
    if (KEY_DOWN(VK_ESCAPE))
       {
       // send message to windows to exit
       PostMessage(main_window_handle, WM_DESTROY,0,0);

       // set exit state
       game_state = GAME_STATE_SHUTDOWN;

       } // end if

    } // end if
///////////////////////////////////////////////////////////////
else
if (game_state == GAME_STATE_SHUTDOWN)
   {
   // in this state shut everything down and release resources
   DD_Shutdown();

   // switch to exit state
   game_state = GAME_STATE_EXIT;

   } // end if

// return success
return(1);

} // end Game_Main

///////////////////////////////////////////////////////////////