title: Custom blending equations (shader) for OpenGL
body: <p>I am trying to experiment with different alpha blending equations for transparent objects using OpenGL but it looks like fragment shaders operate on the color of fragments on single objects and cant take into account the scene behind the object. </p>
  
  <p>On the other hand there doesn't seem to be a way to intercept the <a href="https://www.khronos.org/opengl/wiki/Blending" rel="nofollow noreferrer">blending stage</a> with arbitrary GLSL code, for example I can't think of a way to reproduce <a href="https://en.wikipedia.org/wiki/Blend_modes#Soft_Light" rel="nofollow noreferrer">soft light blend mode</a> with the current OpenGL primitives. </p>
  
  <p>Is there a way to reconcile these?</p>