perf(tv): rasterize axis-aligned gradients into strip textures

Skia's dithered gradient shaders cost ~10ms per full-screen pass on Mali-class TV GPUs: the two spotlight scrims alone were ~20ms of a 27ms raster frame, while flat blended quads at the same coverage are ~free. Bake axis-aligned LinearGradients once into cached 1x1024 premultiplied strip textures drawn as stretched quads (shader fallback for unsupported shapes and the first frame). Converted the spotlight, TV detail backdrop, app-bar scrims, rail bleed, person-card overlay, and the video-controls scrim, which now also keeps one widget type across hasFrame flips so the controls subtree survives in-place source switches. Scripted-browse on a Mali-G31 box: draw p50 27.5ms -> 7.1ms, swap block 20.3ms -> 0.9ms, janky draws 69% -> 2%; screenshots pixel-identical.
2026-07-02 11:41:25 +02:00
parent 1059658515
commit b08b3b846a
7 changed files with 376 additions and 72 deletions
@@ -0,0 +1,96 @@
+import 'dart:typed_data';
+import 'dart:ui' as ui;
+
+import 'package:flutter/material.dart';
+import 'package:flutter/rendering.dart';
+import 'package:flutter_test/flutter_test.dart';
+import 'package:plezy/widgets/rasterized_gradient.dart';
+
+/// The strip texture must composite identically to Skia's gradient shader.
+/// Translucent non-black ramps are the regression case: rgba8888 strips are
+/// consumed premultiplied, so straight-alpha baking renders them far too
+/// bright (a white fade-to-transparent scrim becomes an opaque sheet).
+void main() {
+  Future<ui.Image> capture(WidgetTester tester, Key key) async {
+    final boundary = tester.renderObject<RenderRepaintBoundary>(find.byKey(key));
+    late ui.Image image;
+    await tester.runAsync(() async => image = await boundary.toImage());
+    return image;
+  }
+
+  Future<List<int>> centerColumn(WidgetTester tester, ui.Image image) async {
+    late ByteData bytes;
+    await tester.runAsync(() async => bytes = (await image.toByteData())!);
+    final x = image.width ~/ 2;
+    final column = <int>[];
+    for (var y = 0; y < image.height; y += 8) {
+      final offset = (y * image.width + x) * 4;
+      column.addAll([bytes.getUint8(offset), bytes.getUint8(offset + 1), bytes.getUint8(offset + 2)]);
+    }
+    return column;
+  }
+
+  testWidgets('strip path matches the gradient shader over a colored background', (tester) async {
+    final gradient = LinearGradient(
+      begin: Alignment.topCenter,
+      end: Alignment.bottomCenter,
+      colors: [
+        Colors.white.withValues(alpha: 0.8),
+        Colors.white.withValues(alpha: 0.4),
+        Colors.white.withValues(alpha: 0.0),
+      ],
+      stops: const [0.0, 0.4, 1.0],
+    );
+
+    // Bake ahead of the build so RasterizedGradient paints the strip from
+    // its first frame instead of the (trivially identical) shader fallback.
+    late ui.Image? strip;
+    await tester.runAsync(() async => strip = await RasterizedGradient.prebake(gradient));
+    expect(strip, isNotNull, reason: 'axis-aligned gradient must bake to a strip');
+
+    const rasterizedKey = Key('rasterized');
+    const shaderKey = Key('shader');
+    Widget sample(Key key, Widget gradientBox) => RepaintBoundary(
+      key: key,
+      child: SizedBox(
+        width: 64,
+        height: 256,
+        child: Stack(
+          fit: StackFit.expand,
+          children: [
+            const ColoredBox(color: Color(0xFF406080)),
+            gradientBox,
+          ],
+        ),
+      ),
+    );
+
+    await tester.pumpWidget(
+      Directionality(
+        textDirection: TextDirection.ltr,
+        child: Center(
+          child: Row(
+            mainAxisSize: MainAxisSize.min,
+            children: [
+              sample(rasterizedKey, RasterizedGradient(gradient: gradient)),
+              sample(shaderKey, DecoratedBox(decoration: BoxDecoration(gradient: gradient))),
+            ],
+          ),
+        ),
+      ),
+    );
+
+    final rasterized = await centerColumn(tester, await capture(tester, rasterizedKey));
+    final shader = await centerColumn(tester, await capture(tester, shaderKey));
+
+    for (var i = 0; i < shader.length; i++) {
+      // Skia dithers its gradient shader; the strip doesn't. Allow a couple
+      // of levels of noise — the premul bug is off by 50+ on this ramp.
+      expect(
+        (rasterized[i] - shader[i]).abs(),
+        lessThanOrEqualTo(3),
+        reason: 'channel ${i % 3} at sample ${i ~/ 3}: strip=${rasterized[i]} shader=${shader[i]}',
+      );
+    }
+  });
+}