Weird Sprite Handler

no-reply@allegro.cc (horizon981) — Sun, 13 Aug 2006 13:18:52 +0000

I wanted to make a program to load sprites from a sprite strip and a simple sprite engine.
The proble is that I get a black screen only. The application doesn't crash, just that you get to see nothing.
If anything from the code is not clear to you, please don't hesitate to ask, it's really important.
The code:

1/*Advanced Sprite Animation with RLE Sprites*/
2#include 
3 
4struct Sprites
5{
int x, y;
int xSpeed, ySpeed;
int xDir, yDir;
bool isAlive;
int delay;
int curFrame, maxFrame;
12}monster;
13 
14 
15void setup_sprites(Sprites *Sprite)
16{
Sprite->x = rand()%100;
Sprite->y = rand()%100;
Sprite->xSpeed = 2; //--Move 2 pixels per keystroke
Sprite->ySpeed = 0; //--Vertical movement
Sprite->xDir = 1; //Default = +ve
Sprite->yDir = 0; //No movement in Y direction
Sprite->isAlive = true;
Sprite->delay = 20;
Sprite->curFrame = 0;
Sprite->maxFrame = 3;
27}

29void update_sprite(Sprites *Sprite)
30{
if(Sprite->xDir == 1)    
Sprite->x += Sprite->xSpeed;
else if(Sprite->xDir == -1)
Sprite->x -= Sprite->xSpeed;
else
Sprite->x += 0; 

if(Sprite->yDir == 1)    
Sprite->y += Sprite->ySpeed;
else if(Sprite->yDir == -1)
Sprite->y -= Sprite->ySpeed;
else
Sprite->y += 0;

Sprite->curFrame++;

if(Sprite->curFrame>3)
 Sprite->curFrame = 0;
49}
50 
  
52int main()
53{
allegro_init();
set_color_depth(desktop_color_depth());
set_gfx_mode(GFX_AUTODETECT_WINDOWED, 640, 480, 0, 0);

install_keyboard();

BITMAP *buffer  = create_bitmap(640, 480);
BITMAP *image = load_bitmap("monster.bmp", NULL);

if(!buffer)
{
allegro_message("Double Buffering Failed, outta here...");
allegro_exit();
return -1;
}
if(!image)
{
allegro_message("Sprite loading failed... outta here");
allegro_exit();
return -1;          
}

Sprites *Sprite = &monster;  
//--Lock Screen
acquire_screen();

//--Set up initial behaviour of sprites
setup_sprites(Sprite);

while(!key[KEY_ESC])
{
int x = image->w/(Sprite->maxFrame+1)*Sprite->curFrame;
int y = 0;
                     
update_sprite(Sprite);
rest(Sprite->delay);
blit(image, buffer, x, y, Sprite->x, Sprite->y, 
     (image->w/(Sprite->maxFrame+1)), image->h);

blit(buffer, screen, 0, 0, 0, 0, 640, 480); 
}
release_screen();

destroy_bitmap(image);
destroy_bitmap(buffer);
allegro_exit();
return 0;
101}
102END_OF_MAIN();

Thanks in advance!

no-reply@allegro.cc (Kauhiz) — Sun, 13 Aug 2006 13:27:23 +0000

Quote:

struct Sprites
{
int x, y;
int xSpeed, ySpeed;
int xDir, yDir;
bool isAlive;
int delay;
int curFrame, maxFrame;
}monster;

void setup_sprites(Sprites *Sprite)

That's wrong. Do

struct Sprites
{
 int x, y;
 int xSpeed, ySpeed;
 int xDir, yDir;
 bool isAlive;
 int delay;
 int curFrame, maxFrame;
}Sprites;

Edit: For clarification, right now you have a struct called monster, but use a struct called Sprites. Also, again, drop the ; at END_OF_MAIN()

no-reply@allegro.cc (horizon981) — Sun, 13 Aug 2006 14:13:09 +0000

In case you didn't notice, Sprite is a pointer to struct monster.

no-reply@allegro.cc (Kauhiz) — Sun, 13 Aug 2006 14:21:41 +0000

Sprite is declared as Sprites *Sprite. So, what is Sprites?

no-reply@allegro.cc (Kitty Cat) — Sun, 13 Aug 2006 15:04:20 +0000

You're doing more than drawing to the screen between the acquire/release_screen pairs. You don't need to call them at all when you only draw to the screen once per loop.

no-reply@allegro.cc (horizon981) — Sun, 13 Aug 2006 15:28:26 +0000

Sprites is a structure that holds all the data about a sprite. monster is an instance of this structure. Sprite is a pointer to monster. Does that help?

no-reply@allegro.cc (Kauhiz) — Sun, 13 Aug 2006 15:56:12 +0000

Wait, I think you're right, what was I looking at... Well, Kitty Cat is right anyway, the acquire/release bitmap calls are placed horribly, either get rid of them all together or just put them around the blitting (right now they're both outside the main loop )

no-reply@allegro.cc (horizon981) — Sun, 13 Aug 2006 17:36:44 +0000

Thanks a lot!!
What was wrong with the screen acquire cammands?

no-reply@allegro.cc (Jonny Cook) — Sun, 13 Aug 2006 17:43:46 +0000

If I remember correctly, you can only do drawing operations between acquire/release_screen() calls. And they are only beneficial when you draw to the screen multiple times in a row, which you aren't doing.

no-reply@allegro.cc (miran) — Sun, 13 Aug 2006 18:58:00 +0000

You should throw the book you're reading out the window. It's no good.

no-reply@allegro.cc (Kauhiz) — Sun, 13 Aug 2006 19:27:14 +0000

The screen needs to be acquired before it's drawn to. After that, it needs to be released. Blit does this automatically, unless you do it manually. The reason you may want to do it manually, is that if you draw a lot of stuff to the screen, it's better to acquire the screen then draw everything and release the screen than acquire before and release after every blit. The way you had it would release the screen after the user presses ESC, which just terrible.

no-reply@allegro.cc (horizon981) — Sun, 13 Aug 2006 20:02:18 +0000

So, is double buffering as good as manually acquiring the screen?

no-reply@allegro.cc (BAF) — Sun, 13 Aug 2006 20:05:45 +0000

You should be double buffering anyway. And its like comparing apples to oranges, double buffering has nothing to do with acquiring the screen.

no-reply@allegro.cc (Kikaru) — Mon, 14 Aug 2006 00:20:17 +0000

From my limited experience, double buffering eliminates flickering, really helps when using a custom mouse pointer.

Also, I've never used acquire_screen() - release_screen() functions, and all my games have run pretty well.

1	/Advanced Sprite Animation with RLE Sprites/
2	#include
3
4	struct Sprites
5	{
6	int x, y;
7	int xSpeed, ySpeed;
8	int xDir, yDir;
9	bool isAlive;
10	int delay;
11	int curFrame, maxFrame;
12	}monster;
13
14
15	void setup_sprites(Sprites *Sprite)
16	{
17	Sprite->x = rand()%100;
18	Sprite->y = rand()%100;
19	Sprite->xSpeed = 2; //--Move 2 pixels per keystroke
20	Sprite->ySpeed = 0; //--Vertical movement
21	Sprite->xDir = 1; //Default = +ve
22	Sprite->yDir = 0; //No movement in Y direction
23	Sprite->isAlive = true;
24	Sprite->delay = 20;
25	Sprite->curFrame = 0;
26	Sprite->maxFrame = 3;
27	}
28
29	void update_sprite(Sprites *Sprite)
30	{
31	if(Sprite->xDir == 1)
32	Sprite->x += Sprite->xSpeed;
33	else if(Sprite->xDir == -1)
34	Sprite->x -= Sprite->xSpeed;
35	else
36	Sprite->x += 0;
37
38	if(Sprite->yDir == 1)
39	Sprite->y += Sprite->ySpeed;
40	else if(Sprite->yDir == -1)
41	Sprite->y -= Sprite->ySpeed;
42	else
43	Sprite->y += 0;
44
45	Sprite->curFrame++;
46
47	if(Sprite->curFrame>3)
48	Sprite->curFrame = 0;
49	}
50
51
52	int main()
53	{
54	allegro_init();
55	set_color_depth(desktop_color_depth());
56	set_gfx_mode(GFX_AUTODETECT_WINDOWED, 640, 480, 0, 0);
57
58	install_keyboard();
59
60	BITMAP *buffer = create_bitmap(640, 480);
61	BITMAP *image = load_bitmap("monster.bmp", NULL);
62
63	if(!buffer)
64	{
65	allegro_message("Double Buffering Failed, outta here...");
66	allegro_exit();
67	return -1;
68	}
69	if(!image)
70	{
71	allegro_message("Sprite loading failed... outta here");
72	allegro_exit();
73	return -1;
74	}
75
76	Sprites *Sprite = &monster;
77	//--Lock Screen
78	acquire_screen();
79
80	//--Set up initial behaviour of sprites
81	setup_sprites(Sprite);
82
83	while(!key[KEY_ESC])
84	{
85	int x = image->w/(Sprite->maxFrame+1)*Sprite->curFrame;
86	int y = 0;
87
88	update_sprite(Sprite);
89	rest(Sprite->delay);
90	blit(image, buffer, x, y, Sprite->x, Sprite->y,
91	(image->w/(Sprite->maxFrame+1)), image->h);
92
93	blit(buffer, screen, 0, 0, 0, 0, 640, 480);
94	}
95	release_screen();
96
97	destroy_bitmap(image);
98	destroy_bitmap(buffer);
99	allegro_exit();
100	return 0;
101	}
102	END_OF_MAIN();