Hi folks,
im having some problems using OpenGL with SDL.
The way i am doing i can blit images on screen but i get a wierd result in the alpha channel. I am using the following code:
Initing SDL:
39 glEnable( GL_TEXTURE_2D );
40 glEnable( GL_ALPHA_TEST );
41 glAlphaFunc( GL_GREATER,0.01f);
42
43 glClearColor( 0.0f, 0.0f, 0.0f, 0.0f );
44 glViewport( 0,
45 0,
46 Config::SCREEN_WIDTH,
47 Config::SCREEN_HEIGHT
48 );
49
50 glClear( GL_COLOR_BUFFER_BIT );
51 glMatrixMode( GL_PROJECTION );
52 glLoadIdentity();
53
54 glOrtho(0.0f,
55 Config::SCREEN_WIDTH,
56 Config::SCREEN_HEIGHT,
57 0.0f,
58 -1.0f,
59 1.0f);
60
61 glMatrixMode( GL_MODELVIEW );
62 glLoadIdentity();
63
64 if( glGetError() != GL_NO_ERROR ) { throw SDLError(); }
Screen draw:
81 glBindTexture(GL_TEXTURE_2D, img->texture);
82 glBegin( GL_QUADS );
83 //Top-left vertex (corner)
84 glTexCoord2i( 0, 0 );
85 glVertex3f( x, y, 0 );
86 //Top-right vertex (corner)
87 glTexCoord2i( 1, 0 );
88 glVertex3f( x+img->width, y, 0 );
89 //Bottom-right vertex (corner)
90 glTexCoord2i( 1, 1 );
91 glVertex3f( x+img->width, y+img->height, 0 );
92 //Bottom-left vertex (corner)
93 glTexCoord2i( 0, 1 );
94 glVertex3f( x, y+img->height, 0 );
95 glEnd();
Texture creating:
68 glGenTextures( 1, &texture );
69 glBindTexture( GL_TEXTURE_2D, texture );
70
71 glTexImage2D( GL_TEXTURE_2D,
72 0,
73 GL_RGBA,
74 surface->w,
75 surface->h,
76 0,
77 GL_RGBA,
78 GL_UNSIGNED_BYTE,
79 surface->pixels);
80
81 glTexParameteri( GL_TEXTURE_2D, GL_TEXTURE_MIN_FILTER, GL_LINEAR );
82 glTexParameteri( GL_TEXTURE_2D, GL_TEXTURE_MAG_FILTER, GL_LINEAR );
83 SDL_FreeSurface(surface);
And the image used has a power of 2 size and was created by the following code:
26 image = SDL_CreateRGBSurface(
27 SDL_SWSURFACE,
28 w,
29 h,
30 Config::SCREEN_BPP,
31 #if SDL_BYTEORDER == SDL_LIL_ENDIAN /* OpenGL RGBA masks */
32 0x000000FF,
33 0x0000FF00,
34 0x00FF0000,
35 0xFF000000
36 #else
37 0xFF000000,
38 0x00FF0000,
39 0x0000FF00,
40 0x000000FF
41 #endif
42 );
if i try using one of the following modes all the screen gets black:
glEnable(GL_BLEND);
glBlendFunc(GL_SRC_ALPHA, GL_ONE_MINUS_SRC_ALPHA);
glEnable( GL_ALPHA_TEST );
glAlphaFunc( GL_GREATER,0.1f);
Using only SDL the image is displayed correctly but if i use opengl the alpha channel gets black like this:
http://img48.imageshack.us/img48/3606/opengltd4.png
can someone help me??
thanks in advance!
