webGL - How do I set up a stencil buffer alongside a frame buffer and use it?

Question

Wandering if anyone could help me out. I am currently using webGL to render my content to a frame buffer so that it can be used as a texture for other parts of the project. This works like a champ. However I now need to make use of a stencil buffer whilst rendering to the frame buffer as I am using it to mask. I cant seem to figure out how to create / attach a stencil buffer to work with my frame buffer? This is my code so far:

// next time to create a frame buffer and texture
this.frameBuffer = gl.createFramebuffer();
this.texture = gl.createTexture();

gl.bindTexture(gl.TEXTURE_2D,  this.texture);
gl.texParameteri(gl.TEXTURE_2D, gl.TEXTURE_MAG_FILTER, gl.LINEAR);
gl.texParameteri(gl.TEXTURE_2D, gl.TEXTURE_MIN_FILTER, gl.LINEAR);
gl.texParameteri(gl.TEXTURE_2D, gl.TEXTURE_WRAP_S, gl.CLAMP_TO_EDGE);
gl.texParameteri(gl.TEXTURE_2D, gl.TEXTURE_WRAP_T, gl.CLAMP_TO_EDGE);
gl.bindFramebuffer(gl.FRAMEBUFFER, this.framebuffer );

gl.bindFramebuffer(gl.FRAMEBUFFER, this.frameBuffer );
gl.framebufferTexture2D(gl.FRAMEBUFFER, 
                        gl.COLOR_ATTACHMENT0, 
                        gl.TEXTURE_2D, 
                        this.texture,0);

So my question is, how do I create and then use a stencil buffer along with the frameBuffer created above?

Thanks all!

Answer 1

Continued where your code left off

var renderbuffer = gl.createRenderbuffer();
gl.bindRenderbuffer(gl.RENDERBUFFER, renderBuffer);
gl.renderbufferStorage(gl.RENDERBUFFER, gl.STENCIL_INDEX8, width, height);
gl.framebufferRenderbuffer(
   gl.FRAMEBUFFER, gl.STENCIL_ATTACHMENT, gl.RENDERBUFFER, renderbuffer);

Note: you didn't set the size of your texture by calling texImage2D. The size of the stencil buffer must match the size of texture.

Also, using just a stencil buffer is not guaranteed to work on all platforms. OpenGL ES unfortunately does not guarantee any combination of framebuffer attachments to work :( Fortunately WebGL does. It only requires 3 combinations to work.

• COLOR_ATTACHMENT0 = RGBA/UNSIGNED_BYTE texture
• COLOR_ATTACHMENT0 = RGBA/UNSIGNED_BYTE texture + DEPTH_ATTACHMENT = DEPTH_COMPONENT16 renderbuffer
• COLOR_ATTACHMENT0 = RGBA/UNSIGNED_BYTE texture + DEPTH_STENCIL_ATTACHMENT = DEPTH_STENCIL renderbuffer

So, you have 3 options.

1. Allocate only a stencil buffer and just pray it works

2. Allocate only a stencil buffer, attach it and the color texture, then call gl.checkFramebufferComplete to see if it works. If not print an error

3. Use a DEPTH_STENCIL attachment which is guaranteed to work everywhere.

I'd choose #3 :) In which case the code changes to

var renderbuffer = gl.createRenderbuffer();
gl.bindRenderbuffer(gl.RENDERBUFFER, renderBuffer);
gl.renderbufferStorage(gl.RENDERBUFFER, gl.DEPTH_STENCIL, width, height);
gl.framebufferRenderbuffer(
   gl.FRAMEBUFFER, gl.DEPTH_STENCIL_ATTACHMENT, gl.RENDERBUFFER, renderbuffer);