Run the view transform after the detail stage, in a pass of its own

The fused pass stops at "linear working values" when a sharpener, a
blur or a repair follows, and the detail passes convolve what it hands
on. Until now it handed on the rendering: the base curve, and since the
last commit the view transform, ran before the store. So every kernel
worked on display-referred values while its comments promised the
opposite — D19's second finding.

A fused pass composed for a detail stage now stops before the view
transform, and carries a second shader, `ComposedShader::view`, composed
from the same inputs. It runs the same prologue, for the positions a
fragment reads (a film's grain seeds from `source_px`) and the corners
it blacks out, takes its colour from the detail stage's result bound
where the sample cache would be, and runs the view transform, the
output transform and the mask reveal. `render_detailed` dispatches it
after the last detail pass, in the same encoder.

So no detail pass encodes any more. Every pass writes an intermediate,
the last one included, which retires three things that existed only to
make the last pass encode: `writes_output` and the runner's second
layout, the body-less resolve pass for an active kernel with nothing to
draw at this scale, and capture sharpening's pass-through, which now
emits no pass at all. An empty chain is a whole render: the view pass
reads the fused result directly. The detail stage no longer takes an
output space either, so `compose_detail_for` folds into
`compose_detail` and the space is named once, on the fused half.

The cost is one full-render read and write per frame when a detail
stage exists, and a third intermediate for a one-pass chain.

core/dr-gpu/tests/capture_sharpen.rs

@@ -87,8 +87,7 @@ fn sharpened(amount: f32, radius: f32, threshold: f32) -> EditGraph {
 fn render(pass: &mut AdjustPass, graph: &EditGraph, source: &DemosaicedImage, out: u32) -> Vec<u8> {
     let shader = graph.compose_for(ColourSpace::Srgb);
     let scale = graph.render_scale(source.size(), (out, out));
-    let detail =
-        graph.compose_detail_for(scale.full_size(), scale.render_size(), ColourSpace::Srgb);
+    let detail = graph.compose_detail(scale.full_size(), scale.render_size());
     let key = graph.invalidation().through(Affects::Colour);
     pass.render_detailed(source, &shader, out, out, None, &detail, key)
         .expect("render");
@@ -413,7 +412,7 @@ fn dragging_the_amount_recompiles_nothing_and_reallocates_nothing() {
     let pipelines = pass.cached_detail_pipelines();
     let allocations = pass.detail_allocations();
     assert_eq!(pipelines, 2, "one per axis of the separable mask");
-    assert_eq!(allocations, 2, "the colour result, and one hand-off");
+    assert_eq!(allocations, 3, "the colour result, and the ping-pong pair");
     assert_eq!(pass.detail_dispatches(), 2);
     assert_eq!(pass.colour_dispatches(), 1);
 
@@ -453,13 +452,12 @@ fn dragging_the_amount_recompiles_nothing_and_reallocates_nothing() {
 
 #[test]
 fn a_render_too_coarse_for_the_radius_still_reaches_the_screen() {
-    // The failure mode that the pass-through exists to prevent, proved on a
-    // device rather than argued about. With the radius finer than a render
-    // pixel the operation declines to sharpen — but it is still active, so the
-    // fused pass has already been composed to hand on unclipped linear values,
-    // and something must still perform the output transform. An empty chain
-    // here would not be a soft preview: it would be a hard error out of
-    // `render_detailed`, on the most ordinary develop view there is.
+    // Proved on a device rather than argued about. With the radius finer than
+    // a render pixel the operation declines to sharpen — but it is still
+    // active, so the fused pass has already been composed to hand on
+    // unclipped linear values, and something must still perform the output
+    // transform. Since D19 that is the view pass, whatever the chain holds:
+    // the chain is empty and the frame is still whole.
     let Some(ctx) = ctx() else { return };
     const SOURCE: u32 = 128;
     const RENDER: u32 = 32; // a quarter scale, as a fit view of a large frame
@@ -471,7 +469,16 @@ fn a_render_too_coarse_for_the_radius_still_reaches_the_screen() {
 
     let mut pass = AdjustPass::new(&ctx);
     let sharp = render(&mut pass, &graph, &source, RENDER);
-    assert_eq!(pass.detail_dispatches(), 1, "one pass, and it only encodes");
+    assert_eq!(
+        pass.detail_dispatches(),
+        0,
+        "nothing to sharpen at this scale"
+    );
+    assert_eq!(
+        pass.view_dispatches(),
+        1,
+        "and the view pass finishes the frame"
+    );
 
     // And what reaches the screen is the unsharpened picture, not a black
     // frame, a linear one, or a guess.