module pixel_generator(switches,rst,hpos,vpos,red,green,blue);
   // horizontal and vertical input positions (10 bits apiece)
   input [9:0]		hpos;
   input [9:0]		vpos;

   // switches to control behavior
	input [3:0]		switches;

   // global reset
   input 	    rst;
   

   // red, green, and blue output pixel values.
   output 	    red;
   reg		    red;
   output 	    green;
   reg		    green;
   output 	    blue;
   reg 		    blue;

  	reg [2:0]	 setred;
	reg [2:0]	 setgreen;
	reg [2:0]	 setblue;

   // ball position on screen
   reg [9:0] 	    ball_x;
   reg [9:0] 	    ball_y;

   // ball velocity
   reg [9:0] 	    ball_vx;
   reg [9:0] 	    ball_vy;

   // need to invert velocity
   reg 		    bounce_x;
   reg 		    bounce_y;

	// paddle positions on screen
	reg[9:0]		paddle_a_y;
	reg[9:0]		paddle_b_y;


   // screen dimensions
   parameter 	    H_SIZE = 10'd800;
   parameter 	    V_SIZE = 10'd600;

   // playing field parameters
   parameter 	    BORDER = 10'd4;
   parameter 	    X_MIN = BORDER;
   parameter 	    X_MAX = H_SIZE - BORDER;
   parameter 	    Y_MIN = BORDER;
   parameter 	    Y_MAX = V_SIZE - BORDER;

   // ball parameters
   parameter 	    BALL_WIDTH = 10'd16;
   parameter 	    BALL_HEIGHT = 10'd12;

   reg 		    frame_index;
   reg [9:0] 	    frame;

   reg 		    do_reset_x;
   reg 		    do_reset_y;

	// paddle parameters
	parameter		PADDLE_WIDTH = 10'd8;
	parameter		PADDLE_HEIGHT = 10'd36;
	parameter		PADDLE_DIST_FROM_WALL = 10'd8;
	parameter		PADDLE_START = 10'd282;
	parameter		PADDLE_A_X_MIN = X_MIN + PADDLE_DIST_FROM_WALL;
	parameter		PADDLE_A_X_MAX = X_MIN + PADDLE_DIST_FROM_WALL + PADDLE_WIDTH;
	parameter		PADDLE_B_X_MIN = X_MAX - PADDLE_DIST_FROM_WALL - PADDLE_WIDTH;
	parameter		PADDLE_B_X_MAX = X_MAX - PADDLE_DIST_FROM_WALL;

	reg			 do_reset_p;

	initial begin
		setred = 0;
		setgreen = 0;
		setblue = 0;
	end

	always @(hpos or vpos) begin
		red = |setred;
		green = |setgreen;
		blue = |setblue;
	end

   // draw a blue border around playfield
   always @(hpos or vpos) begin
      if (hpos < X_MIN || hpos > X_MAX || vpos < Y_MIN || vpos > Y_MAX)
			setblue[0] = 1;
      else
			setblue[0] = 0;
   end

   // draw a yellow ball
   always @(hpos or vpos or ball_x or ball_y) begin
      if ((hpos >= ball_x) && (hpos < (ball_x + BALL_WIDTH)) 
			&& (vpos >= ball_y) && (vpos < (ball_y + BALL_HEIGHT)))
		begin
			setred[0] = 1;
		   setgreen[0] = 1;
		end else begin
		  setred[0] = 0;
		  setgreen[0] = 0;
	  	end
   end // always @ (hpos or vpos or ball_x or ball_y)

	always @(hpos or vpos) begin
		if ((hpos >= PADDLE_A_X_MIN) && (hpos < PADDLE_A_X_MAX)
			&& (vpos >= paddle_a_y) && (vpos < (paddle_a_y + PADDLE_HEIGHT)))
			setred[1] = 1;
		else
			setred[1] = 0;
	end

	always @(hpos or vpos) begin
		if ((hpos >= PADDLE_B_X_MIN) && (hpos < PADDLE_B_X_MAX)
			&& (vpos >= paddle_b_y) && (vpos < (paddle_b_y + PADDLE_HEIGHT)))
			setred[2] = 1;
		else
			setred[2] = 0;
	end

   // generate a frame_index pulse at the beginning of a frame
   always @(hpos or vpos) begin
      if (vpos == 0 && hpos == 0)
			frame_index = 1;
      else
			frame_index = 0;
   end

   // keep a running count of the frame number
   always @(posedge frame_index) begin
      if (frame < 10'd600)
			frame = frame + 1;
      else
			frame = 0;
   end

   always @(negedge rst) begin
      do_reset_x = 1;
      do_reset_y = 1;
		do_reset_p = 1;

   end

   // update the ball position once per frame
   // do x and y as separate tasks
   always @(posedge frame_index) begin
      // at reset, put the ball in center court
      if (do_reset_x == 1) begin
	 		ball_x = X_MAX / 2;
		  	ball_vx = 3;
			do_reset_x = 0;
		end else begin
			// bounce the ball off the sides
			if (ball_x < X_MIN
				|| (ball_x < PADDLE_A_X_MAX
					&& !(ball_x < PADDLE_A_X_MIN)
					&& !((ball_y + BALL_HEIGHT) < paddle_a_y || ball_y > (paddle_a_y + PADDLE_HEIGHT)))
				|| (ball_x < PADDLE_B_X_MAX
					&& !(ball_x < PADDLE_B_X_MIN)
					&& !((ball_y + BALL_HEIGHT) < paddle_b_y || ball_y > (paddle_b_y + PADDLE_HEIGHT))))
				ball_vx = 3;		//bounce right
			else if (ball_x > (X_MAX - BALL_WIDTH)
				|| ((ball_x + BALL_WIDTH) > PADDLE_A_X_MIN 
					&& !((ball_x + BALL_WIDTH) > PADDLE_A_X_MAX)
					&& !((ball_y + BALL_HEIGHT) < paddle_a_y || ball_y > (paddle_a_y + PADDLE_HEIGHT)))
				|| ((ball_x + BALL_WIDTH) > PADDLE_B_X_MIN
					&& !((ball_x + BALL_WIDTH) > PADDLE_B_X_MAX)
					&& !((ball_y + BALL_HEIGHT) < paddle_b_y || ball_y > (paddle_b_y + PADDLE_HEIGHT))))
				ball_vx = -3;		//bounce left
			ball_x = ball_x + ball_vx;
   	end
	end // always @ (posedge frame_index)
   
   always @(posedge frame_index) begin
		// at reset, put the ball in center court
		if (do_reset_y == 1) begin
			ball_y = Y_MAX / 2;
			ball_vy = 3;
			do_reset_y = 0;
		end else begin
			// bounce the ball off the top and bottom
			if (ball_y < Y_MIN
				 || (ball_y < (paddle_a_y + PADDLE_HEIGHT)
				 		&& !((ball_y + BALL_HEIGHT) < (paddle_a_y + PADDLE_HEIGHT)) 
				     	&& !((ball_x + BALL_WIDTH) < PADDLE_A_X_MIN || ball_x > PADDLE_A_X_MAX))
				 || (ball_y < (paddle_b_y + PADDLE_HEIGHT)
				 		&& !((ball_y + BALL_HEIGHT) < (paddle_b_y + PADDLE_HEIGHT)) 
						&& !((ball_x + BALL_WIDTH) < PADDLE_B_X_MIN || ball_x > PADDLE_B_X_MAX)))
				ball_vy = 3;
			else if (ball_y > (Y_MAX - BALL_HEIGHT)
				 || ((ball_y + BALL_HEIGHT) > paddle_a_y
				 		&& !(ball_y > paddle_a_y)
						&& !((ball_x + BALL_WIDTH) < PADDLE_A_X_MIN || ball_x > PADDLE_A_X_MAX))
				 || ((ball_y + BALL_HEIGHT) > paddle_b_y
				 		&& !(ball_y > paddle_b_y)
				     	&& !((ball_x + BALL_WIDTH) < PADDLE_B_X_MIN || ball_x > PADDLE_B_X_MAX)))
				ball_vy = -3;
			ball_y = ball_y + ball_vy;
		end
	end // always @ (posedge frame_index)

 always @(posedge frame_index) begin
		// at reset, put the ball in center court
		if (do_reset_p == 1) begin
			paddle_a_y = PADDLE_START;
			paddle_b_y = PADDLE_START;
			do_reset_p = 0;
		end else begin
			if (^switches[1:0])
				if (switches[0] && paddle_a_y > Y_MIN)
					paddle_a_y = paddle_a_y - 1;
				else if (switches[1] && (paddle_a_y + PADDLE_HEIGHT) < Y_MAX)
					paddle_a_y = paddle_a_y + 1;

			if (^switches[3:2])
				if (switches[2] && paddle_b_y > Y_MIN)
					paddle_b_y = paddle_b_y - 1;
				else if (switches[3] && (paddle_b_y + PADDLE_HEIGHT) < Y_MAX)
					paddle_b_y = paddle_b_y + 1;

		end
	end // always @ (posedge frame_index)

endmodule