Shaders: Anime4K presets in-session and in Settings

Vendored Anime4K v4.0.1 GLSL (MIT), extracted to app support once per
version. Presets A/B/C/A+A/B+B/C+A in HQ and Fast per Anime4K's mpv
templates, plus custom files. Shader button in the video controls
(works in fullscreen), Ctrl+1..6 / Ctrl+0, live apply with read-back,
failures fall back to Off with a toast. Render mode detected from
mpv's GL log; warns when on the software path. Docs include the
Jellyfin client section.

Co-Authored-By: Claude Opus 5.5 <noreply@anthropic.com>

apps/desktop/lib/src/shaders/shader_presets.dart

@@ -0,0 +1,87 @@
+import 'dart:io';
+
+// Anime4K v4.0.1 presets, file for file as in Anime4K's mpv templates
+// (md/Template/GLSL_Mac_Linux_{High,Low}-end/input.conf): HQ = the
+// high-end GPU set, Fast = the low-end set.
+
+/// Anime4K release the shipped files come from (assets/shaders/anime4k).
+const anime4kVersion = '4.0.1';
+
+enum ShaderPreset {
+  off('Off'),
+  a('Mode A'),
+  b('Mode B'),
+  c('Mode C'),
+  aa('Mode A+A'),
+  bb('Mode B+B'),
+  ca('Mode C+A'),
+  custom('Custom shaders');
+
+  final String label;
+  const ShaderPreset(this.label);
+
+  /// The six Anime4K modes, in Ctrl+1..Ctrl+6 order.
+  static const modes = [a, b, c, aa, bb, ca];
+
+  bool get isAnime4k => modes.contains(this);
+}
+
+enum ShaderQuality {
+  hq('HQ'),
+  fast('Fast');
+
+  final String label;
+  const ShaderQuality(this.label);
+}
+
+/// "Mode A (HQ)", "Off", "Custom shaders".
+String shaderLabel(ShaderPreset preset, ShaderQuality quality) =>
+    preset.isAnime4k ? '${preset.label} (${quality.label})' : preset.label;
+
+const _clamp = 'Anime4K_Clamp_Highlights.glsl';
+const _down = [
+  'Anime4K_AutoDownscalePre_x2.glsl',
+  'Anime4K_AutoDownscalePre_x4.glsl',
+];
+
+/// Anime4K file names of [preset] in mpv order; empty for off/custom.
+List<String> anime4kFiles(ShaderPreset preset, ShaderQuality quality) {
+  final hq = quality == ShaderQuality.hq;
+  // Big/small network sizes: HQ uses VL then M, Fast uses M then S.
+  final big = hq ? 'VL' : 'M';
+  final small = hq ? 'M' : 'S';
+  String restore(String size) => 'Anime4K_Restore_CNN_$size.glsl';
+  String soft(String size) => 'Anime4K_Restore_CNN_Soft_$size.glsl';
+  String up(String size) => 'Anime4K_Upscale_CNN_x2_$size.glsl';
+  String denoise(String size) => 'Anime4K_Upscale_Denoise_CNN_x2_$size.glsl';
+  return switch (preset) {
+    ShaderPreset.off || ShaderPreset.custom => const [],
+    ShaderPreset.a => [_clamp, restore(big), up(big), ..._down, up(small)],
+    ShaderPreset.b => [_clamp, soft(big), up(big), ..._down, up(small)],
+    ShaderPreset.c => [_clamp, denoise(big), ..._down, up(small)],
+    ShaderPreset.aa => [
+        _clamp, restore(big), up(big), restore(small), ..._down, up(small)
+      ],
+    ShaderPreset.bb => [
+        _clamp, soft(big), up(big), ..._down, soft(small), up(small)
+      ],
+    ShaderPreset.ca => [
+        _clamp, denoise(big), ..._down, restore(small), up(small)
+      ],
+  };
+}
+
+/// Every file some preset needs: exactly what assets/shaders/anime4k holds.
+List<String> get anime4kAllFiles => {
+      for (final p in ShaderPreset.modes)
+        for (final q in ShaderQuality.values) ...anime4kFiles(p, q),
+    }.toList()
+      ..sort();
+
+/// mpv's path-list separator: ';' on Windows, ':' elsewhere.
+String shaderListSeparator({bool? windows}) =>
+    (windows ?? Platform.isWindows) ? ';' : ':';
+
+/// The `glsl-shaders` value for [paths].
+String joinShaderPaths(List<String> paths, {bool? windows}) =>
+    paths.join(shaderListSeparator(windows: windows));