From: chris_mears AT softhome DOT net (Chris Mears)
Newsgroups: comp.os.msdos.djgpp
Subject: Allegro & GDB
Organization: CHOAM
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Date: Sun, 19 Sep 1999 07:05:34 GMT
To: djgpp AT delorie DOT com
DJ-Gateway: from newsgroup comp.os.msdos.djgpp
Reply-To: djgpp AT delorie DOT com

Hi all,

In the middle of the night, I had the idea to write a bouncy-ball
program in Allegro.  I did, and it seems to work pretty well.
However, when I run it under the debugger, GDB, the ball is not drawn
at all.  I can't figure it out.

Does anyone know what's going on?

Thanks,

Chris

<file starts here>

/*
 *	Bouncy Ball.
 * (Allegro)
 */

#include <allegro.h>
#include <stdio.h>
#include <stdlib.h>
#include <dos.h>

#define	MAX_SPEED	4

#define	BALL_SIZE	25

#define	SCREEN_X		640
#define	SCREEN_Y		480
#define	COLOR_DEPTH	16

struct ball
	{
	int		x;
	int		y;
	int		xSpeed;
	int		ySpeed;
	int		width;
	int		height;
	BITMAP*	pic;
	BITMAP*	buffer;
	};

void init_ball(struct ball* b);
void move_ball(struct ball* b);
void draw_ball(struct ball* b, BITMAP* bmp);
void erase_ball(struct ball* b, BITMAP* bmp);

int main(void)
	{
	struct ball	b;
	BITMAP*		vscreen;

	allegro_init();
	install_keyboard();
	install_timer();

	printf("Loading graphics mode...\n");

	printf("Attempting to use resolution %dx%d\n", SCREEN_X, SCREEN_Y);

	set_color_depth(COLOR_DEPTH);
	if (set_gfx_mode(GFX_AUTODETECT, SCREEN_X, SCREEN_Y, 0, 0) < 0)
		{
		printf("Graphics mode could not be initialised...\n");
		printf("Allegro says: %s\n", allegro_error);
		abort();
		}

	init_ball(&b);

	vscreen = create_bitmap(SCREEN_W, SCREEN_H);
	if (vscreen == NULL)
		{
		abort();
		}
	clear(vscreen);

	while (!keypressed())
		{
      move_ball(&b);
		draw_ball(&b, vscreen);
		blit(vscreen, screen, 0, 0, 0, 0, SCREEN_W, SCREEN_H);
		erase_ball(&b, vscreen);
		}

	clear_keybuf();

	return 0;
	}

void init_ball(struct ball* b)
	{
	b->x = rand() % (SCREEN_W - b->width);
	b->y = rand() % (SCREEN_H - b->height);
	b->xSpeed = (rand() % MAX_SPEED) + 1;
	b->ySpeed = (rand() % MAX_SPEED) + 1;

	b->pic = create_bitmap(BALL_SIZE, BALL_SIZE);

	if (COLOR_DEPTH == 8)
		clear_to_color(b->pic, MASK_COLOR_8);
	else if (COLOR_DEPTH == 16)
		clear_to_color(b->pic, MASK_COLOR_16);
	else
		clear(b->pic);

	circlefill(b->pic, BALL_SIZE / 2 + 1, BALL_SIZE / 2 + 1, BALL_SIZE
/ 2,
			makecol(255, 255, 255));

	b->buffer = create_bitmap(BALL_SIZE, BALL_SIZE);
	clear(b->buffer);		/* Redundant. */

	b->width = BALL_SIZE;
	b->height = BALL_SIZE;
	}

void move_ball(struct ball* b)
	{
	if ((b->x + b->width + b->xSpeed) > SCREEN_W)
		b->xSpeed = -((rand() % MAX_SPEED) + 1);

	if ((b->y + b->height + b->ySpeed) > SCREEN_H)
		b->ySpeed = -((rand() % MAX_SPEED) + 1);

	if ((b->x + b->xSpeed) < 0)
		b->xSpeed = (rand() % MAX_SPEED) + 1;

	if ((b->y + b->ySpeed) < 0)
		b->ySpeed = (rand() % MAX_SPEED) + 1;

	b->x += b->xSpeed;
	b->y += b->ySpeed;
	}

void draw_ball(struct ball* b, BITMAP* bmp)
	{
	blit(bmp, b->buffer, b->x, b->y, 0, 0, b->width, b->height);
   masked_blit(b->pic, bmp, 0, 0, b->x, b->y, b->width, b->height);
	}

void erase_ball(struct ball* b, BITMAP* bmp)
	{
	blit(b->buffer, bmp, 0, 0, b->x, b->y, b->width, b->height);
	}

<file ends here>