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0 pointsfxtentacle3y ago0 comments

You linked to the software fallback renderer which can be used for cross-platform compatibility. But JUCE also has platform-specific rendering modules.

CoreGraphicsContext::createPath will convert the CPU spline segments to CG spline segments which are then rasterized by CoreGraphics using Metal on the GPU.

https://github.com/juce-framework/JUCE/blob/2b16c1b94c90d0db...

And on Windows 7 and up it'll use the hardware-accelerated Direct2D APIs:

https://github.com/juce-framework/JUCE/blob/2b16c1b94c90d0db...

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Jasper_3y ago· 2 in thread

You mentioned using the OpenGL context, and this code is used by the OpenGL context.

CoreGraphics does not use the GPU.

Direct2D uses a approach which tesselates paths into triangles on the CPU. It is similar to the JUCE code in that the GPU is used for coverage, but it still does not natively render splines on the GPU.

fxtentacleOP3y ago

Juce has a CoreGraphicsMetalLayerRenderer which I believe uses Metal to render CoreGrapghics primitives.

And yes, I agree that JUCE will tesselate the splines into straight lines on the CPU. So technically, they are not fully rendered on GPU. But in practice, the slow rasterization is done on GPU while tesselation only has a negligible performance overhead. For example, I heard that UE4->UE5 removed the GPU tesselation support because it's usually easier to just DMA a new mesh from the CPU on-demand. I would treat that as a strong argument that CPU tesselation is practically never the bottleneck.

Jasper_3y ago

> Juce has a CoreGraphicsMetalLayerRenderer which I believe uses Metal to render CoreGrapghics primitives.

This class is part of a JUCE demo app, and you can read the source code to it if you want. [0] It uses CoreGraphics to render the graphics on the CPU, and then uploads it as a texture to the GPU so it can be used as a CAMetal layer. So, no, the graphics are still rendered on the CPU, with compositing being handled on the GPU.

I don't know why you're confidently saying something incorrect, it took me all of 2 minutes to find the source code and read it.

> For example, I heard that UE4->UE5 removed the GPU tesselation support

I know it's confusing, but GPU tessellation is a completely different thing. The word "tessellation" in graphics means "turn into triangles". In a 2D graphics context, we're turning splines and curves and 2D shapes into triangles. In a 3D graphics context, GPU tessellation refers to a control cage mesh which is adaptively subdivided. These two have nothing in common except that triangles come out the other side. I am not aware of anyone who has tried to use GPU tessellation to render 2D graphics.

GPU tessellation failed for a large number of reasons, but poor performance was one of them. So, you know, doing this sort of work efficiently on the GPU is still an open research problem. Just because it's not efficient to do it on the GPU does not mean the performance overhead is negligible. For rendering big complex vector graphics, tess overhead can easily outweigh rasterization overhead.

[0] https://github.com/juce-framework/JUCE/blob/4e68af7fde8a0a64...

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