Shaders: Abs node; 763 checks

Development.md

@@ -12,7 +12,7 @@ npm run check        # typecheck + lint + format:check + tests, the gate CI runs
                      #   code is lost (tail's is reported), so a red run reads as green
 npm run build        # writes dist/ and regenerates index.html
 ./build.sh           # the same under `set -o pipefail`, for callers that pipe the output
-node tools/seed-e2e.mjs && node tools/e2e.mjs                 # 762 editor checks, screenshots in /tmp/gm-e2e-*.png
+node tools/seed-e2e.mjs && node tools/e2e.mjs                 # 763 editor checks, screenshots in /tmp/gm-e2e-*.png
 GM_STEPS=20 node tools/e2e.mjs                                # or 1-12, or 6,20 — a subset while working on one step
 ./e2e.sh start [GM_STEPS]                                     # the same run detached, see below
 ./e2e.sh status                                               # live progress, or the last run's result
@@ -151,4 +151,4 @@ widths to find click points. The **render device is not in this repo** — `/dev
 and a 1 GB `/dev/shm` come from `container.options` in the runner's own `config.yaml`, which
 applies to every job on that runner. Without them chromium falls back to llvmpipe, which gets
 WebGL 1.0 only. Measured in the job container: `ANGLE (Intel, Vulkan 1.3.230, HD Graphics 630)`,
-WebGL 2.0, and the same 762 checks as here.
+WebGL 2.0, and the same 763 checks as here.

Shaders.md

@@ -38,7 +38,7 @@ fed to a colour port is broadcast to all three channels. A colour cannot be fed
 | **Add**, **Subtract**, **Multiply**, **Divide** | in `a`, `b` (any) · out `result` | Arithmetic, per channel for colours. An unconnected input is the number typed on the node (0, or 1 for the second input of Multiply and Divide). |
 | **Mix** | in `a`, `b` (any), `t` (number) · out `result` | Blends from `a` to `b`: `t` = 0 is `a`, 1 is `b`, beyond that it extrapolates. |
 | **Luminance** | in `color` · out `value` | How bright a colour is (Rec. 709 weights), as one number. |
-| **Sin**, **Floor**, **Fract** | in `value` (any) · out `result` | The sine of a number in radians (one wave every 6.283); rounded down to a whole number; the part after the decimal point (2.75 becomes 0.75, a rising value becomes a sawtooth). Per channel for colours. |
+| **Sin**, **Floor**, **Fract**, **Abs** | in `value` (any) · out `result` | The sine of a number in radians (one wave every 6.283); rounded down to a whole number; the part after the decimal point (2.75 becomes 0.75, a rising value becomes a sawtooth); the distance from 0 with the sign dropped (-0.3 becomes 0.3, a value crossing 0 becomes a V). Per channel for colours. |
 | **Step** | in `edge` (number), `value` (any) · out `result` | 0 while `value` is below `edge`, 1 from `edge` on: a hard cut. Per channel for colours. |
 | **Pow** | in `value` (any), `exponent` (number) · out `result` | `value` to the power of `exponent`: 2 squares it, 0.5 is the square root; an easing curve on `u`, a gamma on a colour. Below 0 the value counts as 0, because GLSL leaves `pow` undefined there (0 to a power of 0 or less is undefined too). Per channel for colours. |