Apply a mask layer's settings as offsets to the global ones

A local adjustment ran as a second chain after every global operation, then blended by the mask. So global contrast -30 with -20 on a face was contrast -30, the rest of the chain, and contrast -20 again on the result, rather than -50 where contrast runs. The two edits compounded in ways neither slider showed; a flattening applied to an already flattened picture is how the shadows of a night shot went magenta. A layer's setting is now an offset from its default, added to the global setting (clamped to the parameter's range; a moved switch or choice replaces it) and run at that operation's own place in the chain. At each operation the global fragment and each touching layer's combined fragment read the same input colour, and the pixel moves by each layer's weighted difference: c_g + sum w_i (c_i - c_g). At full weight that is the combined setting exactly, at zero the global result exactly, and no setting is applied twice. An offset that brings an operation back to neutral emits an empty version, which undoes the global setting inside the mask. Blending the colours rather than the uniforms is deliberate: the tone curve and colour mixer emit code only for the channels and bands that are touched, so the global and combined versions of one operation need not share a uniform set. A photograph with no masks compiles to the same shader byte for byte. Test: global -30 with a whole-frame layer at -20 renders within one count of global -50.
2026-09-26 20:43:02 -04:00
parent 8392cf772e
commit fc54523093
3 changed files with 489 additions and 119 deletions
@@ -1135,3 +1135,76 @@ fn two_shown_masks_are_drawn_each_in_its_own_colour() {
        "between them, alpha shows black: ({r}, {g}, {b})"
    );
 }
+
+/// Render a mid-grey-and-shadows frame through `chain` and `stack`.
+fn render_chain(
+    ctx: &GpuContext,
+    chain: &[Box<dyn dr_pipeline::operation::Operation>],
+    stack: &MaskStack,
+    field: Option<&LabelField>,
+) -> Vec<u8> {
+    // A ramp, so both ends of the tonal range are in the comparison.
+    let data: Vec<u8> = (0..SIZE * SIZE)
+        .flat_map(|i| {
+            let v = ((i % SIZE) * 255 / (SIZE - 1)) as u8;
+            [v, v / 2, v, 255]
+        })
+        .collect();
+    let source = DemosaicedImage::from_rgba8(ctx, &data, SIZE, SIZE).expect("upload");
+    let shader = compose_full(
+        chain,
+        &Framing::new(),
+        ColourSpace::Srgb,
+        stack,
+        &SpotSet::new(),
+        &[],
+    );
+    let mut masks = MaskPass::new(ctx).expect("mask pass");
+    let array = masks
+        .render(stack, field, None, None, SIZE, SIZE)
+        .expect("rasterise");
+    let mut adjust = AdjustPass::new(ctx);
+    adjust
+        .render_masked(&source, &shader, SIZE, SIZE, Some(array))
+        .expect("render");
+    adjust.export_pixels().expect("readback").0
+}
+
+fn contrast_chain(v: f32) -> Vec<Box<dyn dr_pipeline::operation::Operation>> {
+    let mut chain = ops::chain();
+    chain
+        .iter_mut()
+        .find(|o| o.descriptor().id.0 == "contrast")
+        .expect("contrast")
+        .set_param(ParamId("contrast"), v);
+    chain
+}
+
+/// A layer's setting is an offset to the global one, applied once: global
+/// −30 with a whole-frame layer at −20 is exactly global −50 — not −30 and
+/// then −20 again on the result, which is what a layer used to do.
+#[test]
+fn a_whole_frame_layer_adds_its_setting_to_the_global_one() {
+    let Some(ctx) = ctx() else {
+        eprintln!("no GPU adapter; skipping");
+        return;
+    };
+    let mut layer = MaskLayer::new("m1", whole_frame());
+    layer.set_param("contrast", ParamId("contrast"), -20.0);
+    let mut stack = MaskStack::new();
+    stack.push(layer);
+
+    let field = split_field(&ctx);
+    let offset = render_chain(&ctx, &contrast_chain(-30.0), &stack, Some(&field));
+    let direct = render_chain(&ctx, &contrast_chain(-50.0), &MaskStack::new(), None);
+    let worst = offset
+        .iter()
+        .zip(&direct)
+        .map(|(a, b)| a.abs_diff(*b))
+        .max()
+        .unwrap();
+    assert!(
+        worst <= 1,
+        "layer offset differs from the summed setting by {worst}"
+    );
+}