How to change color of a monocrome alpha texture in OpenGl?

You could give a vertex color to the triangles, using the texture for transparency.
Maybe this helps: https://learnopengl.com/Advanced-OpenGL/Blending

JoeJ said:
Maybe this helps: https://learnopengl.com/Advanced-OpenGL/Blending

Like many many others, I also started the OpenGl path with leranopengl.com, so yes, alpha blending is already working correctly for all the sprites.

You can take a look if you like, my graphics section is pretty much like many others and should be simple to follow: https://notabug.org/TooOld2Rock-nRoll/ArcadeFighterDemo/src/master/lib/ArcadeFighter/inc/graphics

Other people seam to make it work, in the past at least…

Learnopengl.com uses the FreeType library and renders one texture per glyph, which is not very economical, and forces the single red channel to the alpha field at the shader. I really would like to avoid creating a special shader just for fonts, it would require duplication of many features making it a bug nesting ground.

Thanks for the suggestion though, I will play around with the blending options and see if any of them makes a difference.

TooOld2rock-nRoll said:
I will play around with the blending options and see if any of them makes a difference.

It should work after soem trial and error. Personally i did it for a mobile game - render a quad with alpha blending from alpha texture, the vertex color could be changed per glyph. Using OpenGL ES 1.0 i had no shaders at all.

Found it!

GL_ALPHA is deprecated, the modern way of doing this is with swizzle!

First swizzle the texture to use GL_RED in all RGBA fields with:

static GLint swizzleMask[] = {GL_RED, GL_RED, GL_RED, GL_RED};
glTexParameteriv(GL_TEXTURE_2D, GL_TEXTURE_SWIZZLE_RGBA, swizzleMask);

(you can compound the literals in the function call for the mask, but I'm using cpp and would like to avoid the warning at compilation)

And then load the monocrome texture as usual, all the other rendering behavior previously implemented will work with no need for special shader treatment.

glTexImage2D (GL_TEXTURE_2D, 0, GL_RED, width, height, 0, GL_RED, GL_UNSIGNED_BYTE, data);