Loading an RGB bitmap with alpha?

OpenGL OpenGL: Basic Coding
1

If I have a texture in 24-bit RGB format and I want to treat a color as ‘transparent alpha’, say magenta (ff00ff), is there a way to load into GL as an RGBA texture with an alpha channel? Or must I pre-convert the image into an RGBA format and then load the texture?

2

I guess you need to “pre-convert”. I don’t know anything about using an arbitrary color as transparency.

3

Hmm I still get solid black pixels. I wonder do I need to handle this in the fragment shader?

If the color picked by the sampler2D() has an alpha value of 0.0, I suppose I must somehow blend with what is already there in the front buffer?

Right now my basic fragment shader looks like:

#version 330

uniform sampler2D tex;

in vec2 texPos;
in vec3 fragPos;

out vec4 outFragColor;

void main()
{
	vec4 tex_color;
	tex_color = texture2D(tex, texPos);

	outFragColor = tex_color;
}

Do I A) need to create my own framebuffer to do so?
or B) can somehow blend with the default buffer?

Right now it is very simple I am trying to draw bitmap font glyphs on the screen, obviously with transparency around the actual glyph itself.

4

Try this.

5

Oh goodie :slight_smile: I thought it might have been deprecated for some reason.

I added two lines to my GL init function and it works fine now.

glEnable(GL_BLEND);
glBlendFunc( GL_SRC_ALPHA, GL_ONE_MINUS_SRC_ALPHA );