Can you render to stencil buffer?

Hello, :chimpanzee_amused:

Basically, I have made a texture

 stencilTex = new Texture2D(camW, camH, Image.Format.Depth24Stencil8);

How can I run a fragment shader that can output to this texture?
I have tried:

depthBuffer = new FrameBuffer(camW, camH, 1);

But this throws an exception for this Texture format.
If I do:


I assume this binds the stencilTex to be read not written to. In that case it’s no good.

Now a little information about the problem I’m trying to solve. I have a fragment shader that outputs materialIDs per fragment. I’d like to store these ids in stencil buffer. Then for each material, there will be a pass with stencil operation to render the material’s matching fragments.

If there’s no way to render to stencil buffer, I suppose I could render to Texture of type eg. GL_R8UI, and copy its data to the stencilTex with CPU, but I’d like to avoid needless GPU-CPU transfers if possible. Also jme3 does not have Image.Format.R8UI, is there a reason why it doesnt have this type?

Thanks. :chimpanzee_amused:

One year ago, I used stencil buffer for my deferred pipeline.


source: jme3_ext_deferred/Pass4LBuffer.xtend at master · davidB/jme3_ext_deferred · GitHub


FYI, for materialId, I don’t used stencil, but 8bit (alpha of the normal texture in a Gbuffer / MRT).

Thank you for the reply. Btw what does depthBuf.slot = -101 do? is -101 some special number?

Yes I can store matID as alpha, but… Let’s say i got 10 different materials, each processing a fullscreen quad. Yes, I can compare the matID inside the fragment shader and discard, but that has two disadvantages: 1. extra frag shader code, 2. Each material processes every pixel. It’s not using an Early Fragment Test, which I wanted to use by using a stencil.

I think I have found a viable solution, instead of using a stencil, a depth buffer will do. :chimpanzee_amused:
I can add a Image.Format.Depth to a FrameBuffer and write to it with gl_FragDepth = float(m_MatId) / 256.0;

Then when rendering materials I can move the fullscreen quad to or from cam to select which pixels a shader will render. :chimpanzee_amused: This way fragments with other matIds should be tested out by the Depth Test.