Can I carry out MSAA for deferred rendering by just rendering the geometry twice?

Question

I have question about 3D rendering. Deferred rendering is very powerful but popular for not being nice to MSAA.

I clearly see why, but I suddenly came up some idea to solve that. It's simple : just do deferred rendering completely, and get screen image on texture. This texture(attached on framebuffer or whatever) is of course not-antialiased.

Here comes further processing : then next, draw full scene again but this time fragment shader looks up the exact same position on pre-rendered texture using texelFetch(). And output that. Done.

It's silly but I think it might work. If we draw the geometry again with deferred-rendered result as the output color, it means we re-render the scene with geometry. So we can now provide super-sampled depth information, and the GPU will be able to perform MSAA with aliased color but super-sampled depth geometry. (It's similar with picking up only the 'center' of fragment and evaluating that on ordinary MSAA process).

I'm not sure whether this description makes sense or not. I tested using opengl, but doing that makes no difference with just deferred-rendering.

Does my idea work?

Answer 1

No, your idea does not work.

If you did not render the initial image with multisampling, reading from it later while doing multisampling will not magically create information that doesn't exist in that image.

In your method, every sample which corresponds to a particular pixel in the multisampled rendering will have the same color value. So if two primitives overlap in a pixel, writing to different samples, it won't matter, since both primitives will be generating the same color. All you would be doing is generating multiple different depth values within a pixel, and that doesn't actually contribute to an antialiased output (directly).