diff --git a/doc/architecture.dot b/doc/architecture.dot
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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;
+}
diff --git a/doc/architecture.md b/doc/architecture.md
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+# Pathfinder 3 Architecture
+
+## Rendering pipeline
+
+
+
+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 (TODO: 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.
+
+
diff --git a/doc/architecture.svg b/doc/architecture.svg
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+
+
+
+
+