Drawing objects based only on layer order with no overdraw

Questions & Answers
1

Hi everybody, my question is a bit complicated, but I’ll do my best to be as clear as possible:

I’m trying to write a shader for a 2.5D game that fulfills the following 2 requirements:

  1. Draw opaque objects in front of each other based solely on the order they are rendered in, as set by their order in layer (which basically happens by default if ZTest is Off & you’re rendering back to front like in the transparent queue).
  2. Produce no overdraw.

My first idea for avoiding overdraw was using ZTest & rendering Front To Back. The problem is: Adding “ZTest Less” gets rid of the overdraw, but the shader no longer draws objects solely based on their rendering order. Objects with lower ZDepth will always be drawn in front of others, no matter their order in layer.

Does anybody have an idea how the 2 requirements could be made to work together in a shader? Basically I’m looking for a way to tell a shader if a pixel has been rendered before and if so (regardless of ZDepth) to skip rendering it again.

One more constraint:
There’s going to be >255 objects on screen using this shader, so I think the stencil buffer wouldn’t work as a solution.

Here’s what the top of my shader-code looks like so far:

`SubShader
{
Tags
{
“Queue”=“Geometry”
“IgnoreProjector”=“True”
“RenderType”=“Opaque”
}

    Cull Back  
    Lighting Off  
    ZTest Less  
    ZWrite On  
    Blend Off  

    Pass  
    {}`

Thanks for reading, if anyone has an idea you’d really help me out! :slight_smile:

2

@jvo3dc helped me to figure this out, but I thought I’d leave the solution here in case somebody else stumbles across this:

This can be done using the stencil buffer by just increasing it everytime something is drawn and than checking for each pixel whether it’s reference value is greater than the stencil buffer value. Looks like this in the shader:

Stencil { Ref 1 Comp Greater Pass IncrSat }