FR: JUCE Vulkan

[parawave]

I found this entertaining thread from 2011.

Juce's not quite ready OpenGL Renderer

Sadly, no… I already spent a long time writing a very cunning path-to-triangle algorithm, but the only way to reliably render it with AA ended up being slower than just creating a texture from the edge table, which is how it works now. It’d probably be fast to use triangles if you were happy to just rely on the device’s multisampling to perform the AA, but as far as I can tell the results with that are (at best) piss-poor, or at worst, not anti-aliased at all. I also found that the quantity of…

Apparently @jules was facing exactly the same problem. It fundamentally comes down to
rendering anti-aliased polygons from a path.

He got quite pissed, people kept posting the same ideas that he already tested. A funny read : D
So from this experience I essentially take the following:

1. Hardware implemented MSAA for vector graphics looks like crap.

2. Optimizing or caching a whole stack of drawing operations is not really feasible, since it’s layered 2D graphics.

3. OpenGL performance suffers from framebuffer switching.

4. For small paths it was not clear if the triangulation costs more than the edge table calculation.

I don’t want to tear up old wounds, but he tried one idea that I haven’t considered before.
Anti-Aliasing via accumulation buffer. To quote the coarse idea:

@jules

For what feels like the thousandth time, this is what I was doing:

1. Bind the framebuffer
2. Clear it
3. Accumulate/jitter the polygon into this buffer to build up a (mono) anti-aliased mask
4. Switch back to the original target context/screen
5. Select the framebuffer as a texture, and use it as a mask to blend the appropriate colour/gradient/image/whatever onto the screen

He got it almost working, but performance was very bad. The problem was that binding / switching frame buffers was very expensive. It might be worth testing the same method in Vulkan.

Why? For once: Framebuffer switching is different.
Vulkan uses render passes and could utilize a sub or multi-pass solution and a mask shader with a more specialized format for this purpose.
And then there is instanced rendering. While the OpenGL version JUCE uses doesn’t allow instanced rendering and it would be necessary to render the same geometry with multiple draw calls, in Vulkan we can draw it instanced with different jitter uniforms or push constants to achieve anti aliased 2D geometry in one call.

I’m not sure how good the “jitter polygon into mono mask” method will look. But it’s worth trying. Seems a lot more general than specialized methods for each shape. And the results are tweakable, the AA quality depends on the amount of draw calls of the polygon.

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Did anyone ever try something similar to anti-aliasing via accumulation buffer?
Also @jules, I know you are busy with SOUL, but if you have any input on this topic I would much appreciate it!