move a bmp by an angle http://www.allegro.cc/forums/view/585630 Allegro.cc Forum Thread matthew@allegro.cc (Matthew Leverton) Sat, 27 May 2006 17:50:40 +0000

Hello

My BITMAP rotate left and right on keypress left and right, but this BITMAP don't go forward in the right angle on keypress up.

I think the problem is in calculating coordonate of the bitmap here :

x += 1 * cos(angle) ;
y += 1 * sin(angle) ;

someone can help the poor English speaker I'm please :)

1#include <allegro.h>
2#include <time.h>
3#include <math.h>
4 
5#define ECRAN_X 800
6#define ECRAN_Y 600
7 
8#define ERREUR(msg) {\
9 set_gfx_mode(GFX_TEXT,0,0,0,0);\
10 allegro_message("Error : \n%s\n", msg);\
11 allegro_exit();\
12 return 1;\
13}
14 
15 
16int main()
17{
18BITMAP *tank;
19BITMAP *page;
20float angle=0;
21float x, y;
22 
23 allegro_init();
24 install_keyboard();
25
26 set_color_depth(16);
27 if (set_gfx_mode(GFX_AUTODETECT_WINDOWED, ECRAN_X, ECRAN_Y, 0, 0) != 0)
28 ERREUR(allegro_error);
29
30 
31 tank=load_bitmap("tank.bmp",NULL);
32 page=create_bitmap(SCREEN_W,SCREEN_H);
33 if (!tank||!page)
34 ERREUR("load image");
35 
36 x=SCREEN_W/2;
37 y=SCREEN_H/2;
38
39 while (1){
40 rest(10);
41 if (key[KEY_ESC] )
42 return(0);
43 if (keypressed()){
44 if (key[KEY_LEFT]){
45 angle-=0.5;
46 }
47 if (key[KEY_RIGHT]){
48 angle+=0.5;
49 }
50 if (key[KEY_UP]){
51 x += 1 * cos(angle) ;
52 y += 1 * sin(angle) ;
53 }
54 }
55 angle=(angle>256)?0:angle;
56 clear_bitmap(page);
57
58 rotate_sprite(page, tank, x, y, ftofix(angle));
59 blit(page,screen,0,0,0,0,SCREEN_W,SCREEN_H);
60 }
61 return 0;
62}
63END_OF_MAIN();

]]> no-reply@allegro.cc (evenzzz) Sat, 27 May 2006 02:29:02 +0000

You have to use radians with sin and cos.

]]> no-reply@allegro.cc (deps) Sat, 27 May 2006 02:30:26 +0000

And cos/sin are in 360 degrees, not 256.

]]> no-reply@allegro.cc (Steve Terry) Sat, 27 May 2006 09:57:35 +0000

ok

I try this but it dont work :

#define DEGREES(x) int((x)/360.0*0xFFFFFF)
#define RADIANS(x) int((x)/2/M_PI*0xFFFFFF)

so i try this :

x += 10 * (cos((angle * 360 / 256 )) * ( M_PI / 180)) ;
y += 10 * (sin((angle * 360 / 256 )) * ( M_PI / 180)) ;

both dont work :(

]]> no-reply@allegro.cc (evenzzz) Sat, 27 May 2006 12:39:10 +0000

Tell me something:

angle * 360 / 256

What the hell does it do?

Try this, but I'm not sure what do you want to do: 

float angle, x, y;

x += cos(angle*M_PI/180);
y += sin(angle*M_PI/180);

]]> no-reply@allegro.cc (CursedTyrant) Sat, 27 May 2006 13:22:03 +0000

angle * 360 / 256 -> because allegro d'ont rotate over 256°

"Allegro uses a bizarre angle format for angles in all graphics commands"

]]> no-reply@allegro.cc (evenzzz) Sat, 27 May 2006 13:39:32 +0000

It should be angle_in_degrees * 256 / 360 to turn degrees to Allegro degrees. It's not that Allegro doesn't rotate over 256°, Allegro's degrees are on a scale between 0 and 255. So a full circle in Allegro's functions is 256 units which is equivalent to 360 degrees. Sin and cos and other standard math functions of course work in radians. So basically you should keep you variables as radians and when you need to pass them to an Allegro function, convert them from radians to Allegro degrees: 

angle_in degrees = angle_in_radians * 180/M_PI;
angle_in_allegro_degrees = angle_in_degrees * 256.0 / 360.0

]]> no-reply@allegro.cc (miran) Sat, 27 May 2006 13:46:49 +0000

Thank all i find the answer

if (key[KEY_UP]){
xenemy += enemy_vel * cos(angle) * dt;
yenemy += enemy_vel * sin(angle) * dt;
}

rotate_sprite(buffer, enemy, xenemy, yenemy, itofix((angle/2/M_PI*256)));

it work great !

]]> no-reply@allegro.cc (evenzzz) Sat, 27 May 2006 14:05:40 +0000
Steve Terry said:

And cos/sin are in 360 degrees, not 256.

Say what?

]]> no-reply@allegro.cc (gnolam) Sat, 27 May 2006 17:50:40 +0000