Added benchmarks and fixed a parallelism bug

readme.md

@@ -18,6 +18,30 @@ Rendering goes through wgpu. On a machine without a GPU, the same shaders run
 on the CPU through Mesa's lavapipe (`vulkan-swrast` on Arch,
 `mesa-vulkan-drivers` on Debian and Ubuntu).
 
+## Performance and fidelity
+
+Lighting and camera fidelity are chosen separately: lighting tiers L0 to L3,
+camera tiers C0 to C3. A row is added here as each tier lands, with its
+measured cost and a sample image from the same scene, so the cost of each step
+up is visible at a glance.
+
+| Tier | Lighting | Camera | RTX 3060 | lavapipe (CPU) | Sample |
+|---|---|---|---|---|---|
+| L0 / C0 | Lambertian surfaces, Earth's and the Moon's limbs exact, eclipse by Earth and the Moon, no shadows on the target, no light from Earth | Pinhole, absolute radiometry to 12-bit DN, no noise or blur | 1.8–2.1 ms | 8–65 ms | [![L0/C0](docs/images/l0-c0.png)](docs/images/l0-c0.png) |
+
+Times are one 1920 x 1080 RGB frame end to end (`submit` to `wait`, readback
+of the DN image included), median of criterion runs, over models from 12 to
+752,000 triangles: the box-wing, Landsat 8 and ICESat-2. The GPU's own work is
+0.3 to 0.6 ms of that; reading 12 MB back and copying it out is most of the
+rest. lavapipe ran on the Intel Core Ultra 9 285K's 24 cores. The run-to-run
+noise is about 3 %. The sample is the Landsat 8 example scene
+(`examples/scenes/landsat8.toml`). `cargo bench -p resolved` reproduces the
+numbers, and `resolved render --timings N` shows the per-pass split.
+
+Planned tiers: L1 adds self-shadowing, Earthshine and albedo maps (M2); C1
+and C2 add lens distortion, blur and detector noise (M3); L2 adds measured
+materials and the atmosphere (M4); L3 is path traced (M5).
+
 ## Usage
 
 ```rust
@@ -149,6 +173,17 @@ them needs a Vulkan driver for the GPU and lavapipe installed. Set
 `WGPU_BACKEND`, `WGPU_ADAPTER_NAME` and the other standard wgpu environment
 variables to steer adapter discovery.
 
+Benchmarks are end-to-end frame times (`submit` then `wait`, readback
+included) on the GPU and on lavapipe, at two resolutions, for the box-wing and,
+once fetched, Landsat 8 and ICESat-2:
+
+```sh
+cargo bench -p resolved
+```
+
+For where a frame's time goes, `resolved render --timings N` adds GPU
+timestamps around each pass (`RendererOptions::profile` in the library).
+
 To see what the GPU tests render, set `RESOLVED_TEST_IMAGES=1`. Each test then
 writes a PNG per device to `target/tmp/test-images/`, scaled so a white
 surface facing the Sun is full white: