Alpha blending and UIView background color

Question

When I draw semitransparent textures with OpenGL, it looks like that I get them blended with EAGLView backgroundColor.

((EAGLView*)my_view).backgroundColor = [UIColor redColor];

opaque property is set to YES.

Now that image looks red, when I change to black it turns to gray(blended with black), to white it becomes white (even semitransparent black). What can it be?

my blending function setting is: src BFP_SRC_ALPHA, dest ONE_MINUS_SRC_ALPHA I tried also(possibly something like premultiplied alpha): src ONE dest GL_ONE_MINUS_SRC_ALPHA - it gives good result, but I get problems when drawing semitransparent quad(not texture).

Answer 1

问题是在预乘alpha中使用src ONE dest GL_ONE_MINUS_SRC_ALPHA，并且args也必须与预乘alpha一起glColor4f（r * a，g * a，b * a，a）