OpenGL ES: How to tint texture with color

Question

I have texture with alpha. And I want to tint it with some color, so it will be colored depending on color alpha value, but overal opacity will be defined only by texture alpha.

This is similar to multi-texturing but with color instead of second texture. How to do it?

(Updated) I have tried to set up texture combiner. Color is tinted fine, but there is problem with alpha - it doesn't take value from texture (like mask). My code at this moment:

glActiveTexture (GL_TEXTURE0); // do we need stage #1?
glTexEnvi(GL_TEXTURE_ENV, GL_TEXTURE_ENV_MODE, GL_COMBINE);
glTexEnvi(GL_TEXTURE_ENV, GL_COMBINE_RGB, GL_INTERPOLATE);
glTexEnvfv(GL_TEXTURE_ENV, GL_TEXTURE_ENV_COLOR, (GLfloat*) &tintColor_);
glTexEnvi(GL_TEXTURE_ENV, GL_SRC0_RGB, GL_TEXTURE);
glTexEnvi(GL_TEXTURE_ENV, GL_SRC1_RGB, GL_CONSTANT);
glTexEnvi(GL_TEXTURE_ENV, GL_SRC2_RGB, GL_CONSTANT);
glTexEnvi(GL_TEXTURE_ENV, GL_OPERAND0_RGB, GL_SRC_COLOR);
glTexEnvi(GL_TEXTURE_ENV, GL_OPERAND1_RGB, GL_SRC_COLOR);
glTexEnvi(GL_TEXTURE_ENV, GL_OPERAND2_RGB, GL_ONE_MINUS_SRC_ALPHA);
// this doesn't work for alpha:
glTexEnvi(GL_TEXTURE_ENV, GL_COMBINE_ALPHA, GL_REPLACE);
glTexEnvi(GL_TEXTURE_ENV, GL_SRC0_ALPHA, GL_TEXTURE);
glTexEnvi(GL_TEXTURE_ENV, GL_OPERAND0_ALPHA, GL_SRC_ALPHA);

Screenshots:

No tinting:

Tint with RGBA = (0, 0.5, 1, 0.5):

Answer 1

Have you tried the above code with glEnable(GL_BLEND)?

Answer 2

You might want to read the OpenGL documentation on transparency, 15.020: "How can I achieve a transparent effect?"

Make sure you are rendering the scene in the right order (your answer does not show any rendering).

Make sure you are using the desired blend function.

Another suggestion I could make is to start using shaders. I always feel a bit more in control when I use them.

Answer 3

I get the same results (running on Android Samsung Galaxy S, for what it's worth). I don't understand why it doesn't work. The docs seem reasonably clear.

For me it works if I use GL_MODULATE for the RGB. It fails again if I use GL_ADD or GL_ADD_SIGNED. Even using GL_MODULATE on the alpha gives the same erroneous behaviour when using those modes on the RGB. You might be stuck with modulating your colours instead of interpolating them.

In summary, this works for me:

glActiveTexture (GL_TEXTURE0); // do we need stage #1?
glTexEnvi(GL_TEXTURE_ENV, GL_TEXTURE_ENV_MODE, GL_COMBINE);
glTexEnvfv(GL_TEXTURE_ENV, GL_TEXTURE_ENV_COLOR, (GLfloat*) &tintColor_);

glTexEnvi(GL_TEXTURE_ENV, GL_COMBINE_RGB, GL_MODULATE);
glTexEnvi(GL_TEXTURE_ENV, GL_SRC0_RGB, GL_TEXTURE);
glTexEnvi(GL_TEXTURE_ENV, GL_SRC1_RGB, GL_CONSTANT);
glTexEnvi(GL_TEXTURE_ENV, GL_OPERAND0_RGB, GL_SRC_COLOR);
glTexEnvi(GL_TEXTURE_ENV, GL_OPERAND1_RGB, GL_SRC_COLOR);

glTexEnvi(GL_TEXTURE_ENV, GL_COMBINE_ALPHA, GL_REPLACE);
glTexEnvi(GL_TEXTURE_ENV, GL_SRC0_ALPHA, GL_TEXTURE);
glTexEnvi(GL_TEXTURE_ENV, GL_OPERAND0_ALPHA, GL_SRC_ALPHA);