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Add very preliminary architecture documentation

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Patrick Walton 2019-01-03 10:35:19 -08:00
parent ad8814fcea
commit f4ed611e56
3 changed files with 203 additions and 0 deletions
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digraph G {
graph[rankdir=LR,fontname="Source Sans Pro"];
node[shape=box,fontname="Source Sans Pro"];
edge[arrowhead=vee];
subgraph cluster_CPU {
Simplify -> Tile -> Cull -> Pack;
label="CPU";
}
subgraph clusterGPU {
Fill -> Shade;
label="GPU";
}
Pack -> Fill;
Paths[shape=none];
Image[shape=none];
Paths -> Simplify;
Shade -> Image;
}

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# Pathfinder 3 Architecture
## Rendering pipeline
![](architecture.svg)
Quoted timings are for the Ghostscript tiger at 1600×1600 pixels, 8-bit RGBA destination, 2017
MacBook Pro, Intel Core i7-7920HQ CPU @ 3.10GHz, (quad-core with hyperthreading), Intel HD Graphics
630 1536 MB.
### CPU
#### Simplify
Across all paths in parallel:
* Apply transforms.
* Convert strokes to fills.
* Make curves monotonic.
#### Tile
Across all paths in parallel:
* Cut paths into 16×16 tiles.
* Approximate curves with lines.
* Flag tiles that consist entirely of a solid color.
#### Cull
Sequentially (<span class="todo">TODO</span>: in parallel):
* Cull tiles occluded by solid-color tiles.
#### Pack
Sequentially:
* Gather up and compress per-instance data produced by the tile pass into batches.
* Upload to GPU.
Approximate CPU time for the tile, cull, and pack passes: 2.2 ms.
### GPU
#### Fill
In parallel:
* Rasterize all edges to an alpha coverage framebuffer (16-bit single-channel floating point).
Approximate GPU time: 2.6 ms.
#### Shade
In parallel:
* Draw solid-color tiles. (Z-buffer is not needed because we did occlusion culling in software.)
* Shade tiles back-to-front using the alpha mask generated during the fill step.
Approximate GPU time: 2.3 ms.
<style>
.todo {
text-transform: lowercase;
font-variant: small-caps;
}
</style>

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