OpenGL ES 1.x blend two textures acording to bitmap in mainmemory

Question

I have two textures (1024x1024, fully MipMapped, both PVRTC-4bitsPerPixel compressed). The Textures are applied on a 3D mesh.

On the CPU I'm updating a 512x512 boolean array.

Now I want to blend texture 2 over texture 1 with respect to this boolean array (true means the respective 4 pixels of texture1 are visible, false means the other texture is visible at this location)

My hardware has two texture units available.

How can I do that?

tito tito · Accepted Answer · 2011-03-04T09:17:03

You can use a specific shader for that. If you have tex1, tex2, and texbool:

# set your textures
glActiveTexture(GL_TEXTURE0)
glBindTexture(GL_TEXTURE_2D, tex1)
glActiveTexture(GL_TEXTURE0+1)
glBindTexture(GL_TEXTURE_2D, tex2)
glActiveTexture(GL_TEXTURE0+2)
glBindTexture(GL_TEXTURE_2D, texbool)

# when you're starting your shader (id is 1 for eg)
glUseProgram(1)
glUniformi(glGetUniformLocation(1, "tex1"), 0)
glUniformi(glGetUniformLocation(1, "tex2"), 1)
glUniformi(glGetUniformLocation(1, "texbool"), 2)

# and now, draw your model as you wish

The fragment shader can be something like:

// i assume that you'll pass tex coords too. Since the tex1 and tex2
// look the same size, i'll assume that for now.
varying vec2 tex1_coords;

// get the binded texture
uniform sample2D tex1;
uniform sample2D tex2;
uniform sample2D texbool;

// draw !
void main(void) {
  vec4 c1 = texture2D(tex1, tex1_coords);
  vec4 c2 = texture2D(tex2, tex1_coords);
  vec4 cbool = texture2D(texbool, tex1_coords / 2.);
  // this will mix c1 to c2, according to cbool.
  // if cbool is 0, c1 will be used, otherwise, it will be c2
  glFragColor = mix(c1, c2, cbool);
}

I didn't test for your example, but that how i'll start to found a solution :)

OpenGL ES 1.x blend two textures acording to bitmap in mainmemory

1 Answers