iPhone – OpenGL texture mixing problem

 glTexEnvi(GL_TEXTURE_ENV, GL_TEXTURE_ENV_MODE, GL_MODULATE);

 glClearColor(1.0f, 1.0f, 1.0f, 1.0f);

 glDisable(GL_DEPTH_TEST) ;

 glEnableClientState(GL_VERTEX_ARRAY);
 glEnableClientState(GL_COLOR_ARRAY);
 glEnable(GL_TEXTURE_2D);
 glBlendFunc(GL_SRC_ALPHA, GL_ONE_MINUS_SRC_ALPHA, GL_ONE_MINUS_SRC_ALPHA); );
 glEnable(GL_BLEND);

I am using OpenGL ES to create a 2D application for the iPad, and I have some problems drawing transparent images.

I am using a fully transparent png-24 image. I am also changing the color of some textures, these textures are white, and some areas are transparent or semi-transparent. Everything is normal. < /p>

However, when I try to set the alpha value of one of the textures, its effect is not normal. The color is too saturated, if the alpha value = 0, I will leave white on a light gray background instead Transparent image. When such a transparent image is on a dark image, the dark image becomes a color similar to the color of the transparent image.

I have tried many parameter combinations of glTexEnvi and glBlendFunc without success.

I don’t know much about OpenGL, so if anyone has any suggestions, it would be great. If there are any details that can help me, please let me know.

Thank you.

p>

This is the initialization of OpenGL

 glTexEnvi(GL_TEXTURE_ENV, GL_TEXTURE_ENV_MODE, GL_MODULATE);

 glClearColor(1.0f, 1.0f, 1.0 f, 1.0f);

 glDisable(GL_DEPTH_TEST);

 glEnableClientState(GL_VERTEX_ARRAY);
 glEnableClientState(GL_COLOR_ARRAY);
 glEnable(GL_TEXTURE_2D); 
 glBlendFunc(GL_SRC_ALPHA, GL_ONE_MINUS_SRC_ALPHA);
 glEnableClientState(GL_TEXTURE_COORD_ARRAY);
 glEnable(GL_BLEND);

It sounds like you told OpenGL that your texture has premultiplied alpha, but it doesn’t.

What parameter glBlendFunc do you use?

More explanation of pre-multiplied alpha