Does this mean, that this “opacity value”(if provided) will override any alpha value of the fragment (for each and every fragment for the rendered object, as this property is defined at object level ) calculated by custom shader as gl_FragColor = vec4(r,g,b,a); for the purpose of blending it to what ever object (destination framebuffer values) is behind it?
Regarding the idea of two different transparencies(sorry for being unclear, I had specific object like fur in mind), I meant type 1, as how we implement transparency for the object such as fur. then type 2 as how we combine this object (fur) fragments with another background object fragments. I hope I am clear now.