Ok I found the issue and resolved it.
In the fragment shader I had this parameter
uniform sampler2D tex_dtex which should have been
uniform sampler2D tex_1 . Then in the program I manually added the depth texture to the quad.
My problem was that I assumed that
quad.setShaderInput("dtex",dtex) passed the texture to the shader, which I don’t think it was. panda3d.org/manual/index.php/Gener … ge_Filters says something along these lines, so it may be an issue with the filter shader generator or still my understanding.