glClear( ... );
glLoadIdentity();
glColor4f( 0.0f, 0.0f, 0.0f, 0.5f );
DrawBox( 100, 100, 100, 100 ); // just draw the square
glEnable( GL_BLEND );
glBelndFunc( GL_DST_ALPHA, GL_ONE );
glColor4f( 1.0f, 1.0f, 1.0f, 1.0f );
DrawBox( 0, 0, 800, 600 );
glDisable( GL_BLEND );
Alpha Blending problem
Author
Hello,
I have a problem with alpha blending in OpenGL.
I'm trying to do 2d hard shadows (described in tutorial on GameDev: "Dynamic 2d Soft Shadows").
Here is some piece of code:
Make sure you've actually got destination alpha. If you don't explicitly ask for it, you may or may not get it. If you don't have it, DST_ALPHA will always be one, and hence you'll get no blending.
(So check the code where you create your window/OpenGL context.)
(So check the code where you create your window/OpenGL context.)
Author
Do you mean PFD_TYPE_RGBA flag in pixelformatdescriptor?
It's done. Here is my pixelformatdescriptor:
I think it's correct.
It's done. Here is my pixelformatdescriptor:
static PIXELFORMATDESCRIPTOR pfd = { sizeof(PIXELFORMATDESCRIPTOR), 1, PFD_DRAW_TO_WINDOW | PFD_SUPPORT_OPENGL | PFD_DOUBLEBUFFER, PFD_TYPE_RGBA, 32, 0, 0, 0, 0, 0, 0, 0, 0, 0, 0, 0, 0, 0, 16, 0, 0, PFD_MAIN_PLANE, 0, 0, 0, 0};I think it's correct.
Mmm.. No, I don't think that's the one. I'm don't use Windows, so I can't say for sure, but I think there should be either a flag for destination alpha or a way to request a number of destination alpha bits. Check the documentation for the pixelformatdescriptor
typedef struct tagPIXELFORMATDESCRIPTOR { // pfd //... BYTE cAlphaBits; I think that's the one. Try setting it to 8
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