Create a new texture from two blended textures

OpenGL OpenGL: Basic Coding
1

Hi guys, I am trying to create a new texture from a background texture but with it’s alpha values set from the colour gradient of another texture. Ie like this:

This is a framework of the C++ code I am using:


unsigned tex_aft(int tex, int copy_tex)
{
    //tex is the texture to set the alpha to, copy_tex is the texture to take the colour gradients from for the alpha values
    GLuint texture = tex, copy_texture = copy_tex;
    glPushAttrib(GL_CURRENT_BIT | GL_COLOR_BUFFER_BIT | GL_ENABLE_BIT);
    glColor4f(1,1,1,1);
    glClear(GL_COLOR_BUFFER_BIT);
    glDisable(GL_BLEND);
    glBindTexture(GL_TEXTURE_2D, texture);
    int w, h;
    glGetTexLevelParameteriv(GL_TEXTURE_2D,0,GL_TEXTURE_WIDTH, &w);
    glGetTexLevelParameteriv(GL_TEXTURE_2D,0,GL_TEXTURE_HEIGHT, &h);
    glEnable(GL_BLEND);
    glBlendFunc(GL_ONE_MINUS_DST_ALPHA, GL_SRC_COLOR);
    glBindTexture(GL_TEXTURE_2D, copy_texture);
    char* bitmap = new char[(h<<(lgpp2(w)+2))|2];  //lgpp2() function is used to get powers of two
    glGetTexImage(GL_TEXTURE_2D, 0, GL_RGBA, GL_UNSIGNED_BYTE, bitmap);
    GLuint tex_new;
    glGenTextures(1, &tex_new);
    glBindTexture(GL_TEXTURE_2D, tex_new);
    glTexImage2D(GL_TEXTURE_2D, 0, 4, w, h, 0, GL_RGBA, GL_UNSIGNED_BYTE, void(bitmap));
    delete[] bitmap;
    glPopAttrib();
    return tex_new;
}

But from what I know you can’t use glBlendFunc to blend bound textures like this, all this code winds up doing is returning a straight replica of the copy_tex. So does anybody here please know what code I could use to blend the two textures like I have described and create a new texture from this?

Thanks for any help.