Comment by vFunct
2 days ago
I still don't understand why we need text rendered offline and stored in an atlas alongside tricks like SDFs, when GPUs have like infinite vertex/pixel drawing capabilities.. Even the article mentions writing glyph curves to an atlas. Why can't the shaders render text directly? There has to be a way to convert bezier to triangle meshes. I'm about to embark on a GPU text renderer for a CAD app and I hope to figure out why soon.
It's simply less expensive in most cases to cache the results of rendering when you render the same glyph over and over. GPUs are fast but not infinitely fast, and they are extremely good at sampling from prerendered textures.
Also it's not just about speed, but power consumption. Once you are fast enough to hit the monitor frame rate then further performance improvements won't improve responsiveness, but you may notice your battery lasting longer. So there's no such thing as "fast enough" when it comes to rendering. You can always benefit from going faster.
> Once you are fast enough to hit the monitor frame rate then further performance improvements won't improve responsiveness
This is not true, if your rendering is faster then you can delay the start of rendering and processing of input to be closer to the frame display time thus reducing input latency.
This is true but very rarely implemented.
That's true, but in this case one can cache the output of e.g. a rendered letter and re-use that, without the intermediate SDF etc. steps.
Of course for e.g. games that breaks if the font size changes, letters rotate and/or become skewed etc.
The triangle density of even a basic font is crazy high at typical display sizes. All modern GPU architectures are very bad at handling high density geometry. It's very inefficient to just blast triangles at the GPU for these cases compared to using an atlas or some other scheme.
Most GPUs dispatch pixel shaders in groups of 4. If all your triangles are only 1 pixel big then you end up with 3 of those shader threads not contributing to the output visually. It's called 'quad overdraw'. You also spend a lot of time processing vertices for no real reason too.
GPUs don't have infinite vertex/pixel drawing capabilities. Rendering text directly is simply more expensive. Yes, you can do it, but you'll be giving up a portion of your frame budget and increasing power usage for no real benefit.
To expand on this, GPUs cannot rasterize text directly because they only work with triangles. You need to either implement the rasterization in shaders or convert the smooth curves in the font into enough triangles that the result doesn't look different (number of triangles required increases with font pixel size).
Triangles are the wrong choice, but otherwise you make a good point. This guy uses an atlas because he renders fonts by super sampling bezier curves using up to 512 samples per pixel, which is very expensive. However, you could e.g. compute the integral of the intersection of the bezier curve area with the subpixel area much faster, which I think could run in real time without a need for an atlas and would be more accurate than supersampling.
GPUs are very fast, but not quite infinite. If you spend your GPU time on text, you can't spend it on something else. And almost always you would like to spend it on something else. Also the more GPU time you require, the faster the minimum required hardware needs to be. Text is cool and important, but maybe not important enough to lose users or customers.
Thin tris -> performance nuke
> Why can't the shaders render text directly?
https://sluglibrary.com/ implements Dynamic GPU Font Rendering and Advanced Text Layout
GPU rasterizers don't do sub-pixel rendering. This is OK for most 3D geometry but for small text you want to take advantage of any additional resolution you can squeeze out.
On the other hand, if you are rendering to an atlas anyway then you don't really need to bother with a GPU implementation for that an can just use an existing software font rasterizer like FreeType to generate that atlas for you.
As far as I understand it, this is exactly what this article is about