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POColors are off in SDL program
 

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  1. POColors are off in SDL program
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    <p>I am currently working on a very simple game using a pure C approach with SDL (and its official extra libraries such as SDL_image) and OpenGL. Right now though I've hit a bit of a stumbling block and I have no idea why it is doing this: the colors are all off when drawn. I am running the program on a Mac currently, but if I remember correctly when I run it in Windows the colors are closer to being correct, but there are still some odd things happening (such as a pure white polygon drawing as yellow).</p> <p>Currently on my Mac all images that are loaded as png files have their color drawn a bit off, and a pure white polygon is drawn as dark green. There are also a few images that are drawn pure white. If I remember correctly on Windows, the images are drawn correctly but the white polygon is yellow, as mentioned earlier. Now I'll post the pertinent code for initialization and loading and such.</p> <pre><code>int main( int argc, char *argv[] ) { //initializing various OpenGL attributes with SDL utilities SDL_GL_SetAttribute( SDL_GL_DOUBLEBUFFER, 1 ); SDL_GL_SetAttribute( SDL_GL_DEPTH_SIZE, 16 ); //needs for 3D SDL_GL_SetAttribute( SDL_GL_RED_SIZE, 8 ); //only needed for systems other than mac osx SDL_GL_SetAttribute( SDL_GL_GREEN_SIZE, 8 ); SDL_GL_SetAttribute( SDL_GL_BLUE_SIZE, 8 ); SDL_GL_SetAttribute( SDL_GL_ALPHA_SIZE, 8 ); /* Set 640x480 video mode */ screen=SDL_SetVideoMode(screen_width,screen_height, 8, videoflags ); if (screen == NULL) { fprintf(stderr, "Couldn't set %dx%dx%d video mode: %s\n", screen_width, screen_height, video_info-&gt;vfmt-&gt;BitsPerPixel, SDL_GetError()); exit(2); } glShadeModel( GL_SMOOTH ); glClearColor( 0.3f, 0.3f, 0.3f, 0 ); glViewport( 0, 0, (GLsizei)screen-&gt;w, (GLsizei)screen-&gt;h ); glMatrixMode( GL_PROJECTION ); glLoadIdentity(); gluOrtho2D( 0.0f, screen-&gt;w, 0.0f, screen-&gt;h ); /*glEnable( GL_BLEND ); glBlendFunc( GL_SRC_ALPHA, GL_ONE_MINUS_SRC_ALPHA );*/ glEnable( GL_ALPHA_TEST ); glAlphaFunc( GL_GREATER, 0.1f ); // Some basic initialization stuff goes here // Assume infinite while loop goes here, except when esc is pressed glClear( GL_COLOR_BUFFER_BIT | GL_DEPTH_BUFFER_BIT ); glMatrixMode( GL_MODELVIEW ); glLoadIdentity(); glEnable( GL_TEXTURE_2D ); draw_gui(); // Things get drawn here glDisable( GL_TEXTURE_2D ); SDL_GL_SwapBuffers(); SDL_Delay( 10 ); // End of while loop, clean up, etc. } </code></pre> <p>Now I'll show the code that actually loads an image into memory:</p> <pre><code>Sprite *gen_sprite( char *file ) { SDL_Surface *buffer = IMG_Load( file ); if( buffer == NULL ) { fprintf( stderr, "Could not load image '%s'\n for reason: %s\n", file, IMG_GetError() ); exit( 3 ); } return gen_sprite_from( buffer ); } Sprite *gen_sprite_from( SDL_Surface *buffer ) { Sprite *sprite; GLuint texture; if( buffer == NULL ) { fprintf( stderr, "NULL surface passed to gen_sprite_from." ); exit( 3 ); } texture = gen_Gl_texture_from( buffer ); if( ( sprite = malloc( sizeof( Sprite ) ) ) == NULL ) { fprintf( stderr, "Malloc failed to allocate space for a Sprite.\n" ); exit( 1 ); } if( ( sprite-&gt;tex = malloc( sizeof( GLuint ) ) ) == NULL ) { fprintf( stderr, "Malloc failed to allocate space for a GLuint.\n" ); exit( 1 ); } sprite-&gt;tex[ 0 ] = texture; sprite-&gt;original = buffer; sprite-&gt;is_animation = 0; sprite-&gt;cur_frame = 0; sprite-&gt;cur_time = 0; sprite-&gt;num_frames = 1; sprite-&gt;frame_time = NULL; return sprite; } Uint32 gen_Gl_texture_from( SDL_Surface *buffer ) { GLuint texture; SDL_Surface *temp; glPixelStorei( GL_UNPACK_ALIGNMENT, 4 ); glGenTextures( 1, &amp;texture ); temp = SDL_CreateRGBSurface( SDL_SWSURFACE, buffer-&gt;w, buffer-&gt;h, 32, 0x000000FF, 0x0000FF00, 0x00FF0000, 0xFF000000 ); SDL_SetAlpha( buffer, 0, SDL_ALPHA_OPAQUE ); SDL_BlitSurface( buffer, NULL, temp, NULL ); glBindTexture( GL_TEXTURE_2D, texture ); //glTexParameteri( GL_TEXTURE_2D, GL_TEXTURE_MAG_FILTER, GL_NEAREST ); //glTexParameteri( GL_TEXTURE_2D, GL_TEXTURE_MIN_FILTER, GL_NEAREST ); glTexParameteri( GL_TEXTURE_2D, GL_TEXTURE_MAG_FILTER, GL_LINEAR ); glTexParameteri( GL_TEXTURE_2D, GL_TEXTURE_MIN_FILTER, GL_LINEAR ); glTexParameteri( GL_TEXTURE_2D, GL_GENERATE_MIPMAP, GL_TRUE ); gluBuild2DMipmaps( GL_TEXTURE_2D, 4, temp-&gt;w, temp-&gt;h, GL_RGBA, GL_UNSIGNED_BYTE, temp-&gt;pixels ); SDL_FreeSurface( temp ); // This just creates white blocks instead of actually loading textures //glPixelStorei( GL_UNPACK_ALIGNMENT, buffer-&gt;format-&gt;BytesPerPixel ); //glGenTextures( 1, &amp;texture ); //glBindTexture( GL_TEXTURE_2D, texture ); //glTexParameteri( GL_TEXTURE_2D, GL_TEXTURE_MAG_FILTER, GL_LINEAR ); //glTexParameteri( GL_TEXTURE_2D, GL_TEXTURE_MIN_FILTER, GL_LINEAR ); //glTexImage2D( GL_TEXTURE_2D, 0, mask_order, buffer-&gt;w, buffer-&gt;h, 0, // mask_order, GL_UNSIGNED_BYTE, buffer-&gt;pixels ); return texture; } </code></pre> <p>At this point, I believe all the code that is pertinent for why colors would be skewed has been posted. Drawing code is very simple and just involves something such as a translation or rotation, binding a texture, and then a simple begin/end block with texcoords and vertices. If anyone can tell me why colors are off, and let me know a good way to make sure that colors are always correct in a cross-platform way (I plan to build on all platforms, which is part of the reason I'm using SDL) I would really appreciate it.</p>
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    1. CO`screen=SDL_SetVideoMode(screen_width,screen_height, 8, videoflags );` Would set up 8 bits for colour... you seem to want 32, don't you?
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    2. COChanging it to 32 (or 0 to let SDL use the current screen's attributes) doesn't seem to do anything different. The drawn polygon is still dark green when it is supposed to be white.
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    3. COInstead of `temp = SDL_CreateRGBSurface( SDL_SWSURFACE, buffer->w, buffer->h, 32, 0x000000FF, 0x0000FF00, 0x00FF0000, 0xFF000000 );` try `temp = SDL_CreateRGBSurface( SDL_SWSURFACE, buffer->w, buffer->h, buffer->format->BitsPerPixel, buffer->format->Rmask, buffer->format->Gmask, buffer->format->Bmask, buffer->format->Amask);`. It might mess up your alpha rendering initially if you haven't set buffer as a surface with alpha enabled.
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