I'm supposed to receive a texture in BC4 format. In OpenGL, i guess this format is called GL_COMPRESSED_RED_RGTC1.

The texture is not really a "texture", more like a data to handle at fragment shader.

Usually, to get colors from a texture within a fragment shader, i do :

uniform sampler2D TextureUnit;
void main()
{
   vec4 TexColor = texture2D(TextureUnit, vec2(gl_TexCoord[0]));
(...)

the result of which is obviously a v4, for RGBA.

But now, i'm supposed to receive a single float from the read. I'm struggling to understand how this is achieved.

Should i still use a texture sampler, and expect the value to be in a specific position (for example, within TexColor.r ?), or should i use something else ?