AllegroGL and translucent textures

no-reply@allegro.cc (samwyse) — Sun, 03 Sep 2006 01:45:47 +0000

I can't get the alpha-channel to work on textures. I've gone so far as to dump the bitmap that I'm using and, yes, the information is there. I'm suspecting that there's a flag somewhere that I'm forgetting to set, but as this is the first time I've tried doing this, I'm not sure what it would be.

Anyway, here's the code I'm using to create the texture (with embedded logging):

1GLuint LoadTexture(char * bmp_name, int translucent = 0)
2{
  GLuint texture_handle;
4 
  // Load the texture
  set_color_depth(32);
  BITMAP* bmp = load_bitmap(bmp_name, 0);
  cerr << "loading " << bmp_name << endl;
  if (translucent) {
    cerr << "setting alpha" << endl;
    set_write_alpha_blender();
    drawing_mode(DRAW_MODE_TRANS, NULL, 0, 0);
    for (int y=0; y<bmp->h; y++)
      for (int x=0; x<bmp->w; x++)
        putpixel(bmp, x, y, 0x77);
    drawing_mode(DRAW_MODE_SOLID, NULL, 0, 0);
  }
  for (int y=0; y<bmp->h; y+=0x55)
    for (int x=0; x<bmp->w; x+=0x55)
      cerr << hex << x << "," << y << ": " << getpixel(bmp,x,y) << endl;
  texture_handle = allegro_gl_make_texture_ex(
      AGL_TEXTURE_HAS_ALPHA, bmp, -1);
  glTexEnvi(GL_TEXTURE_2D, GL_TEXTURE_MAG_FILTER, GL_NEAREST);
  glTexEnvi(GL_TEXTURE_2D, GL_TEXTURE_MIN_FILTER, GL_NEAREST);
  destroy_bitmap(bmp);
  return texture_handle;
27}

And here's what I get when I run it:

1loading clouds2.tga
20,0: c88365
355,0: db9c81
40,55: aa5536
555,55: d59377
6loading drock03048477.tga
70,0: 90b6b6
855,0: 94baba
90,55: 90b6b6
1055,55: 789e9e
11loading water038.tga
12setting alpha
130,0: 77ff795f
1455,0: 77e95d4c
150,55: 77f6684f
1655,55: 77ff7a5e

I've got a half-meg screen dump if you really want to see it, but trust me when I say that you can't see the river bottom through the water. But that does bring up a second small issue. I've noticed that save_bitmap is inverting my screenshots. I presume that this is due to Allegro putting (0,0) in the upper left and OpenGL putting it in the lower left. Is there any way to fix this, or should I resign myself to manually flipping things?

no-reply@allegro.cc (Jakub Wasilewski) — Sun, 03 Sep 2006 04:20:39 +0000

Just to be sure - you do call glBlendFunc and glEnable(GL_BLEND) prior to drawing anything with those textures, right?

You can also try using GL_RGBA instead of the -1 with make_texture_ex to force a pixel format that contains alpha.

no-reply@allegro.cc (ImLeftFooted) — Mon, 04 Sep 2006 01:04:26 +0000

Heres my init code

  if(0 != install_allegro_gl())
      throw "Unable to init Allegro GL.";
  
  allegro_gl_clear_settings();
  allegro_gl_set(AGL_DOUBLEBUFFER, 1);
allegro_gl_set(AGL_RENDERMETHOD, 1);
  allegro_gl_set(AGL_COLOR_DEPTH, settings.colorDepth);
  allegro_gl_set(AGL_RENDERMETHOD, 1);
allegro_gl_set(AGL_Z_DEPTH, 0);
  allegro_gl_set(AGL_SAMPLE_BUFFERS, 0);
  allegro_gl_set(AGL_SAMPLES, 0);
  
  allegro_gl_set(AGL_DONTCARE, AGL_Z_DEPTH | AGL_SAMPLE_BUFFERS | AGL_SAMPLES);
  allegro_gl_set(AGL_SUGGEST, AGL_COLOR_DEPTH | AGL_RENDERMETHOD);
  allegro_gl_set(AGL_REQUIRE, AGL_DOUBLEBUFFER);
  
  set_color_depth(settings.colorDepth);
  
  int mode = GFX_OPENGL;
  
  if((curProfile && curProfile->fullscreen) || (!curProfile && settings.fullscreen)) {
      
  allegro_gl_set(AGL_FULLSCREEN, 1);
  allegro_gl_set(AGL_WINDOWED, 0);
  allegro_gl_set(AGL_SUGGEST, AGL_FULLSCREEN | AGL_WINDOWED);
  mode=GFX_OPENGL_FULLSCREEN;
  }
  else {
      
  allegro_gl_set(AGL_FULLSCREEN, 0);
  allegro_gl_set(AGL_WINDOWED, 1);
  allegro_gl_set(AGL_SUGGEST, AGL_FULLSCREEN | AGL_WINDOWED);
  mode=GFX_OPENGL_WINDOWED;
}
  
  if(0 != set_gfx_mode(mode, settings.screenWidth, settings.screenHeight, 0, 0))
      throw "Unable to set OpenGL graphics mode.";
  
  switch(allegro_gl_get(AGL_COLOR_DEPTH)) {
      
      case 16: set_color_conversion(COLORCONV_32_TO_16);
          break;
      case 24: set_color_conversion(COLORCONV_32_TO_24);
          break;
  }
  
  initAllegro();
  
  allegro_gl_begin();
      glMatrixMode(GL_PROJECTION);
      glLoadIdentity();
      glOrtho(0.0, 640.0, 480.0, 0.0, -1.0, 1.0);
      glMatrixMode(GL_MODELVIEW);
      glLoadIdentity();
      glClearColor(0, 0, 0, 1);
      glTexParameteri(GL_TEXTURE_2D,GL_TEXTURE_MIN_FILTER,GL_NEAREST);
      glTexParameteri(GL_TEXTURE_2D,GL_TEXTURE_MAG_FILTER,GL_NEAREST);
      glTexParameteri(GL_TEXTURE_2D,GL_TEXTURE_WRAP_S,GL_CLAMP_TO_EDGE);
      glTexParameteri(GL_TEXTURE_2D,GL_TEXTURE_WRAP_T,GL_CLAMP_TO_EDGE);
      glBlendFunc(GL_SRC_ALPHA, GL_ONE_MINUS_SRC_ALPHA);
      glDisable(GL_DEPTH_TEST);
      allegro_gl_use_alpha_channel(1);
      allegro_gl_set_texture_format(GL_RGBA8);
      glEnable(GL_BLEND);
      glEnable(GL_TEXTURE_2D);
  allegro_gl_end();

For loading textures i just do this:

texture = allegro_gl_make_texture(src);

Alpha channel works perfect for me.

How are you drawing the texture to the screen?

no-reply@allegro.cc (samwyse) — Mon, 04 Sep 2006 04:26:43 +0000

Jakub Wasilewski said:

Just to be sure - you do call glBlendFunc and glEnable(GL_BLEND) prior to drawing anything with those textures, right?

D'oh! Note to self: In the future, I must make sure that I haven't commented out any code before posting questions to the forum.

Dustin Dettmer said:

Heres my init code

Wow!!! That's some heavy duty code. Thanks for sharing, I think I'll spend the rest of the week-end studying it.

no-reply@allegro.cc (Jakub Wasilewski) — Mon, 04 Sep 2006 04:32:57 +0000

Quote:

Note to self: In the future, I must make sure that I haven't commented out any code before posting questions to the forum.

Nothing to be ashamed of, I just mentioned it because I once made the same error (GL_BLEND disabled) and then wondered for an hour what's wrong.

no-reply@allegro.cc (ImLeftFooted) — Wed, 06 Sep 2006 07:31:24 +0000

If anything doesnt make sense you can ask me about it.

Heres how i draw.

1int texture = allegro_gl_make_texture(src);
2 
3while(!quit) {
4 
  int x = 0;
  int y = 0;
  int w = src->w;
  int h = src->h;
9 
  glBindTexture(GL_TEXTURE_2D, texture);
  
  glBegin(GL_QUADS);
      glTexCoord2f(0.0f, 1.0f);
      glVertex2i(x, y);
      glTexCoord2f(1.0f, 1.0f);
      glVertex2i(x + w, y);
      glTexCoord2f(1.0f, 0.0f);
      glVertex2i(x + w, y + h);
      glTexCoord2f(0.0f, 0.0f);
      glVertex2i(x, y + h);
  glEnd();
22 
  allegro_gl_flip();
24}

1	GLuint LoadTexture(char * bmp_name, int translucent = 0)
2	{
3	GLuint texture_handle;
4
5	// Load the texture
6	set_color_depth(32);
7	BITMAP* bmp = load_bitmap(bmp_name, 0);
8	cerr << "loading " << bmp_name << endl;
9	if (translucent) {
10	cerr << "setting alpha" << endl;
11	set_write_alpha_blender();
12	drawing_mode(DRAW_MODE_TRANS, NULL, 0, 0);
13	for (int y=0; y<bmp->h; y++)
14	for (int x=0; x<bmp->w; x++)
15	putpixel(bmp, x, y, 0x77);
16	drawing_mode(DRAW_MODE_SOLID, NULL, 0, 0);
17	}
18	for (int y=0; y<bmp->h; y+=0x55)
19	for (int x=0; x<bmp->w; x+=0x55)
20	cerr << hex << x << "," << y << ": " << getpixel(bmp,x,y) << endl;
21	texture_handle = allegro_gl_make_texture_ex(
22	AGL_TEXTURE_HAS_ALPHA, bmp, -1);
23	glTexEnvi(GL_TEXTURE_2D, GL_TEXTURE_MAG_FILTER, GL_NEAREST);
24	glTexEnvi(GL_TEXTURE_2D, GL_TEXTURE_MIN_FILTER, GL_NEAREST);
25	destroy_bitmap(bmp);
26	return texture_handle;
27	}

1	loading clouds2.tga
2	0,0: c88365
3	55,0: db9c81
4	0,55: aa5536
5	55,55: d59377
6	loading drock03048477.tga
7	0,0: 90b6b6
8	55,0: 94baba
9	0,55: 90b6b6
10	55,55: 789e9e
11	loading water038.tga
12	setting alpha
13	0,0: 77ff795f
14	55,0: 77e95d4c
15	0,55: 77f6684f
16	55,55: 77ff7a5e

1	if(0 != install_allegro_gl())
2	throw "Unable to init Allegro GL.";
3
4	allegro_gl_clear_settings();
5	allegro_gl_set(AGL_DOUBLEBUFFER, 1);
6	allegro_gl_set(AGL_RENDERMETHOD, 1);
7	allegro_gl_set(AGL_COLOR_DEPTH, settings.colorDepth);
8	allegro_gl_set(AGL_RENDERMETHOD, 1);
9	allegro_gl_set(AGL_Z_DEPTH, 0);
10	allegro_gl_set(AGL_SAMPLE_BUFFERS, 0);
11	allegro_gl_set(AGL_SAMPLES, 0);
12
13	allegro_gl_set(AGL_DONTCARE, AGL_Z_DEPTH \| AGL_SAMPLE_BUFFERS \| AGL_SAMPLES);
14	allegro_gl_set(AGL_SUGGEST, AGL_COLOR_DEPTH \| AGL_RENDERMETHOD);
15	allegro_gl_set(AGL_REQUIRE, AGL_DOUBLEBUFFER);
16
17	set_color_depth(settings.colorDepth);
18
19	int mode = GFX_OPENGL;
20
21	if((curProfile && curProfile->fullscreen) \|\| (!curProfile && settings.fullscreen)) {
22
23	allegro_gl_set(AGL_FULLSCREEN, 1);
24	allegro_gl_set(AGL_WINDOWED, 0);
25	allegro_gl_set(AGL_SUGGEST, AGL_FULLSCREEN \| AGL_WINDOWED);
26	mode=GFX_OPENGL_FULLSCREEN;
27	}
28	else {
29
30	allegro_gl_set(AGL_FULLSCREEN, 0);
31	allegro_gl_set(AGL_WINDOWED, 1);
32	allegro_gl_set(AGL_SUGGEST, AGL_FULLSCREEN \| AGL_WINDOWED);
33	mode=GFX_OPENGL_WINDOWED;
34	}
35
36	if(0 != set_gfx_mode(mode, settings.screenWidth, settings.screenHeight, 0, 0))
37	throw "Unable to set OpenGL graphics mode.";
38
39	switch(allegro_gl_get(AGL_COLOR_DEPTH)) {
40
41	case 16: set_color_conversion(COLORCONV_32_TO_16);
42	break;
43	case 24: set_color_conversion(COLORCONV_32_TO_24);
44	break;
45	}
46
47	initAllegro();
48
49	allegro_gl_begin();
50	glMatrixMode(GL_PROJECTION);
51	glLoadIdentity();
52	glOrtho(0.0, 640.0, 480.0, 0.0, -1.0, 1.0);
53	glMatrixMode(GL_MODELVIEW);
54	glLoadIdentity();
55	glClearColor(0, 0, 0, 1);
56	glTexParameteri(GL_TEXTURE_2D,GL_TEXTURE_MIN_FILTER,GL_NEAREST);
57	glTexParameteri(GL_TEXTURE_2D,GL_TEXTURE_MAG_FILTER,GL_NEAREST);
58	glTexParameteri(GL_TEXTURE_2D,GL_TEXTURE_WRAP_S,GL_CLAMP_TO_EDGE);
59	glTexParameteri(GL_TEXTURE_2D,GL_TEXTURE_WRAP_T,GL_CLAMP_TO_EDGE);
60	glBlendFunc(GL_SRC_ALPHA, GL_ONE_MINUS_SRC_ALPHA);
61	glDisable(GL_DEPTH_TEST);
62	allegro_gl_use_alpha_channel(1);
63	allegro_gl_set_texture_format(GL_RGBA8);
64	glEnable(GL_BLEND);
65	glEnable(GL_TEXTURE_2D);
66	allegro_gl_end();

1	int texture = allegro_gl_make_texture(src);
2
3	while(!quit) {
4
5	int x = 0;
6	int y = 0;
7	int w = src->w;
8	int h = src->h;
9
10	glBindTexture(GL_TEXTURE_2D, texture);
11
12	glBegin(GL_QUADS);
13	glTexCoord2f(0.0f, 1.0f);
14	glVertex2i(x, y);
15	glTexCoord2f(1.0f, 1.0f);
16	glVertex2i(x + w, y);
17	glTexCoord2f(1.0f, 0.0f);
18	glVertex2i(x + w, y + h);
19	glTexCoord2f(0.0f, 0.0f);
20	glVertex2i(x, y + h);
21	glEnd();
22
23	allegro_gl_flip();
24	}