CODEWITHSUNDEEP
webgl2
王仁結
王仁結

Reputation: 19

WebGL2 Copy depth value to default renderbuffer error

In order to implement deferred shading, I used a fbo to do multiple render target.

Now this approach works, but I want to add a sky sphere for the background.

Clearly this sky sphere is not belong to deferred rendering cycle, so I have to render in second pass.

However, in order to render the sky sphere correctly, I have to retrieve depth value, so the deferred render texture will not block the sphere.

To do so, I copy the depth texture from G buffer to default frame buffer:

     gl.bindFramebuffer( gl.READ_FRAMEBUFFER, gDeferredDrawer.FrameBuffer.Context );
     gl.bindFramebuffer( gl.DRAW_FRAMEBUFFER, null ); 
     gl.blitFramebuffer( 0, 0, gl.viewportWidth, gl.viewportHeight, 0, 0, gl.viewportWidth, gl.viewportHeight, gl.DEPTH_BUFFER_BIT, gl.NEAREST );
     gl.bindFramebuffer( gl.FRAMEBUFFER, null );

This approach did not work. WebGL give me this error message:

GL ERROR :GL_INVALID_OPERATION : glBlitFramebufferCHROMIUM: destination framebuffer is multisampled

I really don't know how I did it wrong. There's no clear example in the Internet as far as I know. So could someone please enlighten me?

Upvotes: 1

Views: 978

Answers (1)

user128511
user128511

Reputation:

from the spec section 4.3.2

If SAMPLE_BUFFERS for the draw framebuffer is greater than zero, an INVALID_OPERATION error is generated.

You can't use blitFramebuffer to blit to a multi-sampled destination. You can only read from a multi-sampled source.

So, if you want to use the technique you describe then

  1. Use another framebuffer, combine in that framebuffer then copy to the canvas.

  2. Make the canvas not multi-sampled

    const gl = someCanvas.getContext("webgl2", { antialias: false });

I'm guessing #2 is better in your case. There's no reason to have a multi-sampled canvas if you're actually doing all the rendering that would benefit from multi-sampling on some offscreen framebuffer.

Upvotes: 4

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