feat: Add bloom shader variant and enhance shader architecture in README

Signed-off-by: Hans Kokx <hans.d.kokx@gmail.com>

packages/wolf_3d_flutter/README.md

@@ -86,22 +86,147 @@ For full host wiring examples, see:
 - `lib/renderer/` — renderer host widgets.
 - `lib/managers/` — runtime/session/display/persistence managers.
 - `lib/audio/` — platform-aware audio backends.
-- `shaders/wolf_world.frag` — fragment shader included in package configuration.
+- `shaders/wolf_world.frag` — base fragment shader included in package configuration.
-
+- `shaders/wolf_world_bloom.frag` — bloom-enabled fragment shader variant.
-## Development Commands
-
-From this directory:
-
-```bash
-flutter analyze
-flutter test
-```
 
 ## Integration Notes
 
 - Keep UI/platform concerns in this package or app hosts, not in `wolf_3d_dart`.
 - Use exported APIs from `lib/wolf_3d_flutter.dart` rather than importing private internals from `lib/src` in dependencies.
-- Shader path is declared in this package `pubspec.yaml` and must stay synchronized with renderer usage.
+- Shader paths are declared in this package `pubspec.yaml` and must stay synchronized with renderer usage.
+
+## Shader Architecture And Performance Notes
+
+This package ships two shader variants:
+
+- `shaders/wolf_world.frag` (base pass, no bloom taps)
+- `shaders/wolf_world_bloom.frag` (bloom-enabled variant)
+
+The renderer selects one variant in Dart based on runtime settings. This is a
+performance decision: when bloom is disabled, we do not run bloom sampling code
+at all.
+
+### No-Branch Shader Policy
+
+For package-owned shader sources, do not use `if` statements. Use branchless
+selection patterns (`mix`, `step`, `smoothstep`, mask algebra) instead.
+
+Static check:
+
+```bash
+rg "\bif\s*\(" packages/wolf_3d_flutter/shaders
+```
+
+Expected result: no matches in source shader files.
+
+### Why This Is Different From Dart
+
+If you are primarily a Dart developer, this is the key mindset shift:
+
+- Dart code runs on CPU cores with branch prediction and comparatively cheap
+  control flow.
+- Fragment shaders run across many pixels in parallel on GPU SIMD/SIMT lanes.
+- If neighboring pixels take different branches, the GPU can serialize branch
+  paths (divergence), reducing throughput.
+- Texture reads are usually more expensive than scalar ALU math. Removing bloom
+  work entirely when disabled is often better than trying to gate it inside one
+  shader.
+
+In short: in Dart, `if` can be good structure. In fragment shaders, branchless
+math and pass selection are often better for frame time.
+
+### Dart-Style Thinking vs Shader-Style Thinking
+
+CPU/Dart style:
+
+```dart
+if (effectsEnabled) {
+  uv = warp(uv);
+}
+if (outsideScreen(uv)) {
+  return bezelColor;
+}
+```
+
+Shader style used here:
+
+```glsl
+vec2 effectiveUv = mix(uv, warpedUv, effectsMask);
+float bezelMask = (1.0 - insideMask) * effectsMask;
+vec3 outColor = mix(screenColor, bezelColor, bezelMask);
+```
+
+Both produce feature-equivalent behavior, but the second keeps execution paths
+uniform across fragments.
+
+### Shader Block Guide (What / Why)
+
+1. UV normalization:
+Convert fragment coordinates to 0..1 UV so all sampling math is resolution
+agnostic.
+
+2. Barrel warp:
+Simulates curved CRT glass by pushing UVs outward as radius increases.
+
+3. Inside/outside mask:
+Computes whether warped UV remains on the emissive screen rectangle. This
+replaces branch-based bezel routing.
+
+4. Edge-aware AA:
+Computes local luma span from N/S/E/W neighbors and blends toward neighborhood
+average only where contrast indicates potential aliasing.
+
+5. CRT modulation:
+Applies scanlines, moving sweep, center lift, and vignette to mimic phosphor
+and lens behavior.
+
+6. Bezel shading:
+Uses overflow distance and edge bleed sampling to build depth, inner lip, and
+scene-tinted glow on bezel regions.
+
+7. Bloom variant only:
+Adds three-ring cross taps, brightness gating, and tone mapping. This code is
+in a separate shader so bloom-off mode avoids paying this cost.
+
+### Constant Tuning Reference
+
+- Warp factor: `0.045`
+  Higher = stronger curvature.
+
+- AA blend ceiling: `0.45`
+  Higher = softer edges, more blur risk.
+
+- Scanline band: `0.88 + 0.12 * sin(...)`
+  Lower floor or higher amplitude increases CRT stripe intensity.
+
+- Sweep speed: `uTime * 0.08`
+  Higher = faster sweep line travel.
+
+- Bloom ring radii: `3`, `7`, `13` texels
+  Larger radii spread glow farther but increase halo size.
+
+- Bloom gain: `0.42`
+  Higher = brighter bloom before tone map.
+
+- Tone map: `color / (color + 0.75) * 1.75`
+  Controls highlight rolloff and midtone lift.
+
+### Glossary
+
+- UV: normalized texture coordinates in [0, 1].
+- Luma: perceived brightness estimate from RGB.
+- Mask: scalar 0..1 value used to blend between alternatives.
+- Vignette: edge darkening effect.
+- Tone map: compresses highlights into displayable range.
+- Tap: one texture sample read.
+- Divergence: parallel shader lanes taking different branches.
+
+### Profiling Expectations
+
+- Bloom disabled: base shader variant runs, no bloom taps.
+- Bloom enabled: bloom shader variant runs, additional texture sampling cost.
+- Effects disabled: both shaders still remain branchless; effect contribution is
+  blended out by mask values.
 
 ## Troubleshooting
 

packages/wolf_3d_flutter/lib/renderer/wolf_3d_glsl_renderer.dart

@@ -37,12 +37,16 @@ class WolfGlslRenderer extends BaseWolfRenderer {
 class _WolfGlslRendererState extends BaseWolfRendererState<WolfGlslRenderer> {
   static const int _renderWidth = 960;
   static const int _renderHeight = 600;
+  static const String _baseShaderAsset =
+      'packages/wolf_3d_flutter/shaders/wolf_world.frag';
+  static const String _bloomShaderAsset =
+      'packages/wolf_3d_flutter/shaders/wolf_world_bloom.frag';
 
   final SoftwareRenderer _renderer = SoftwareRenderer();
 
   ui.Image? _renderedFrame;
-  ui.FragmentProgram? _shaderProgram;
+  ui.FragmentShader? _baseShader;
-  ui.FragmentShader? _shader;
+  ui.FragmentShader? _bloomShader;
   bool _isShaderUnavailable = false;
 
   @override
@@ -99,7 +103,11 @@ class _WolfGlslRendererState extends BaseWolfRendererState<WolfGlslRenderer> {
       return const CircularProgressIndicator(color: Colors.white24);
     }
 
-    if (_isShaderUnavailable || _shader == null) {
+    final ui.FragmentShader? activeShader = widget.bloomEnabled
+        ? _bloomShader
+        : _baseShader;
+
+    if (_isShaderUnavailable || activeShader == null) {
       // Keep frames visible even if GLSL initialization failed.
       return Padding(
         padding: const EdgeInsets.all(16.0),
@@ -117,9 +125,8 @@ class _WolfGlslRendererState extends BaseWolfRendererState<WolfGlslRenderer> {
         child: CustomPaint(
           painter: _GlslFramePainter(
             frame: _renderedFrame!,
-            shader: _shader!,
+            shader: activeShader,
             effectsEnabled: widget.effectsEnabled,
-            bloomEnabled: widget.bloomEnabled,
             elapsedSeconds: widget.engine.timeAliveMs / 1000.0,
           ),
           child: const SizedBox.expand(),
@@ -130,15 +137,18 @@ class _WolfGlslRendererState extends BaseWolfRendererState<WolfGlslRenderer> {
 
   Future<void> _loadShader() async {
     try {
-      final ui.FragmentProgram program = await ui.FragmentProgram.fromAsset(
+      final List<ui.FragmentProgram> programs = await Future.wait(
-        'packages/wolf_3d_flutter/shaders/wolf_world.frag',
+        <Future<ui.FragmentProgram>>[
+          ui.FragmentProgram.fromAsset(_baseShaderAsset),
+          ui.FragmentProgram.fromAsset(_bloomShaderAsset),
+        ],
       );
       if (!mounted) {
         return;
       }
       setState(() {
-        _shaderProgram = program;
+        _baseShader = programs[0].fragmentShader();
-        _shader = _shaderProgram!.fragmentShader();
+        _bloomShader = programs[1].fragmentShader();
         _isShaderUnavailable = false;
       });
     } catch (_) {
@@ -157,14 +167,12 @@ class _GlslFramePainter extends CustomPainter {
   final ui.Image frame;
   final ui.FragmentShader shader;
   final bool effectsEnabled;
-  final bool bloomEnabled;
   final double elapsedSeconds;
 
   _GlslFramePainter({
     required this.frame,
     required this.shader,
     required this.effectsEnabled,
-    required this.bloomEnabled,
     required this.elapsedSeconds,
   });
 
@@ -179,7 +187,6 @@ class _GlslFramePainter extends CustomPainter {
       ..setFloat(3, texelY)
       ..setFloat(4, effectsEnabled ? 1.0 : 0.0)
       ..setFloat(5, elapsedSeconds)
-      ..setFloat(6, bloomEnabled ? 1.0 : 0.0)
       ..setImageSampler(0, frame);
 
     final Paint paint = Paint()
@@ -194,7 +201,6 @@ class _GlslFramePainter extends CustomPainter {
     return oldDelegate.frame != frame ||
         oldDelegate.shader != shader ||
         oldDelegate.effectsEnabled != effectsEnabled ||
-        oldDelegate.bloomEnabled != bloomEnabled ||
         oldDelegate.elapsedSeconds != elapsedSeconds;
   }
 }

packages/wolf_3d_flutter/pubspec.yaml

@@ -28,7 +28,7 @@ dev_dependencies:
 flutter:
   shaders:
     - shaders/wolf_world.frag
-
+    - shaders/wolf_world_bloom.frag
   # To add assets to your package, add an assets section, like this:
   # assets:
   #   - images/a_dot_burr.jpeg

packages/wolf_3d_flutter/shaders/wolf_world.frag

@@ -1,100 +1,91 @@
 #include <flutter/runtime_effect.glsl>
 
-// Output surface size in pixels.
+// ----------------------------------------------------------------------------
+// Base Variant (Branchless, No Bloom)
+// ----------------------------------------------------------------------------
+// This shader is the bloom-disabled base variant of the Wolf CRT post-process
+// path.
+//
+// Why keep a separate base file?
+// - Dart/CPU side can select this program when bloom is off.
+// - That avoids bloom texture taps entirely in the hot path.
+// - This is a direct performance optimization, not just stylistic separation.
+//
+// Why branchless math throughout?
+// - Fragment programs run many pixels in lockstep.
+// - Divergent control flow can reduce throughput.
+// - Mask-based selection using mix/step/smoothstep keeps execution uniform.
+//
+// For Dart developers:
+// - Think dataflow over fields of values, not object-level control logic.
+// - Most operations transform scalar/vector fields per pixel.
+// - Alternative outcomes are blended by masks instead of branching.
+
+// Output surface size in pixels for the current draw call.
 uniform vec2 uResolution;
-// One source-texel step in UV space: (1/width, 1/height).
+// One source texel step in UV space: (1/width, 1/height).
+// This keeps neighborhood kernels stable across resolutions.
 uniform vec2 uTexel;
-// 1.0 enables CRT post-process effects, 0.0 keeps only base AA.
+// 1.0 enables CRT warp/scanline stack, 0.0 keeps only base AA stack.
+// Even though this is conceptually boolean, it is expressed as float so the
+// shader can blend outcomes natively with mask math.
 uniform float uEffectsEnabled;
 // Engine time in seconds used to animate scanline travel.
 uniform float uTime;
-// 1.0 enables CRT phosphor bloom glow, 0.0 disables it.
-uniform float uBloomEnabled;
 // Source frame produced by the software renderer.
 uniform sampler2D uTexture;
 
 out vec4 fragColor;
 
-// Perceptual brightness approximation used for edge detection.
+// Perceptual brightness approximation for edge detection.
+// This uses Rec.601-style luma weighting.
 float luma(vec3 color) {
   return dot(color, vec3(0.299, 0.587, 0.114));
 }
 
+// Returns 1.0 when uv is inside [0,1] on both axes, else 0.0.
+// Implemented branchlessly as a product of step() tests.
+float uvInsideMask(vec2 uv) {
+  vec2 lower = step(vec2(0.0), uv);
+  vec2 upper = step(uv, vec2(1.0));
+  return lower.x * lower.y * upper.x * upper.y;
+}
+
 void main() {
-  // Convert fragment coordinates to normalized UV coordinates.
+  // Normalize destination pixel coordinate into UV space.
   vec2 uv = FlutterFragCoord().xy / uResolution;
 
-  if (uEffectsEnabled > 0.5) {
+  // --------------------------------------------------------------------------
-    // Barrel-like warp to emulate curved CRT glass.
+  // 1) CRT warp selection (branchless)
-    vec2 centered = uv * 2.0 - 1.0;
+  // --------------------------------------------------------------------------
-    float radius2 = dot(centered, centered);
+  // The centered radius term drives a mild barrel distortion.
-    centered *= 1.0 + radius2 * 0.045;
+  vec2 centered = uv * 2.0 - 1.0;
-    uv = centered * 0.5 + 0.5;
+  float radius2 = dot(centered, centered);
+  vec2 warpedUv = centered * (1.0 + radius2 * 0.045) * 0.5 + 0.5;
 
-    // Fill outside warped bounds with a darker consumer-TV charcoal bezel.
+  // Mix between linear and warped UV with a float mask.
-    if (uv.x < 0.0 || uv.x > 1.0 || uv.y < 0.0 || uv.y > 1.0) {
+  // In Dart, this is conceptually: useWarped ? warpedUv : uv.
-      vec2 clampedUv = clamp(uv, 0.0, 1.0);
+  vec2 effectiveUv = mix(uv, warpedUv, uEffectsEnabled);
-      vec2 edgeDelta = uv - clampedUv;
-      float overflow = max(abs(edgeDelta.x), abs(edgeDelta.y));
 
-      // Sample near-edge scene colors and spread them onto the bezel.
+  // Clamp once to keep all downstream texture fetches in bounds.
-      vec2 inwardDir = normalize(-edgeDelta + vec2(1e-6));
+  vec2 sampleUv = clamp(effectiveUv, 0.0, 1.0);
-      vec2 bleedStep = vec2(uTexel.x * 1.6, uTexel.y * 1.6);
-      vec2 bleedUv1 = clamp(clampedUv + inwardDir * bleedStep, 0.0, 1.0);
-      vec2 bleedUv2 = clamp(clampedUv + inwardDir * bleedStep * 2.6, 0.0, 1.0);
-      vec2 bleedUv3 = clamp(clampedUv + inwardDir * bleedStep * 4.2, 0.0, 1.0);
-      vec3 edgeBleedColor =
-          texture(uTexture, clampedUv).rgb * 0.52 +
-          texture(uTexture, bleedUv1).rgb * 0.28 +
-          texture(uTexture, bleedUv2).rgb * 0.14 +
-          texture(uTexture, bleedUv3).rgb * 0.06;
-      float edgeBleedLuma = luma(edgeBleedColor);
 
-      // Approximate concave bezel depth by measuring how far this fragment is
+  // 1.0 for screen interior, 0.0 outside.
-      // from the emissive screen boundary in aspect-corrected UV space.
+  float insideMask = uvInsideMask(effectiveUv);
-      vec2 aspectScale = vec2(uResolution.x / max(uResolution.y, 1.0), 1.0);
+  // Bezel contributes only where warped coordinates leave the source screen.
-      float bezelDistance = length(edgeDelta * aspectScale);
+  float bezelMask = (1.0 - insideMask) * uEffectsEnabled;
 
-      // Corners receive less direct bleed because the nearest lit area is
+  // --------------------------------------------------------------------------
-      // diagonally offset, so attenuate glow toward corner regions.
+  // 2) Lightweight edge-aware AA
-      vec2 clampedCentered = clampedUv * 2.0 - 1.0;
+  // --------------------------------------------------------------------------
-      float cornerFactor = smoothstep(0.60, 1.15, length(clampedCentered));
+  // Sample center + cardinal neighbors.
+  vec4 centerSample = texture(uTexture, sampleUv);
+  vec3 sampleN = texture(uTexture, clamp(sampleUv + vec2(0.0, -uTexel.y), 0.0, 1.0)).rgb;
+  vec3 sampleS = texture(uTexture, clamp(sampleUv + vec2(0.0, uTexel.y), 0.0, 1.0)).rgb;
+  vec3 sampleE = texture(uTexture, clamp(sampleUv + vec2(uTexel.x, 0.0), 0.0, 1.0)).rgb;
+  vec3 sampleW = texture(uTexture, clamp(sampleUv + vec2(-uTexel.x, 0.0), 0.0, 1.0)).rgb;
 
-      float verticalShade = 0.88 + 0.07 * (1.0 - (FlutterFragCoord().y / uResolution.y));
+  // Luma span estimates local contrast; high span implies stronger edge.
-      float depthShade = 1.0 - smoothstep(0.0, 0.058, overflow) * 0.34;
-      float grain = sin(FlutterFragCoord().x * 0.21 + FlutterFragCoord().y * 0.11) * 0.006;
-      float moldedHighlight = smoothstep(0.072, 0.0, overflow) * 0.028;
-
-      // Deeper arcade-style profile: tighter, scene-tinted bleed rolloff.
-      float bezelGlow = exp(-bezelDistance * 82.0) * mix(1.0, 0.56, cornerFactor);
-      float innerLip = exp(-bezelDistance * 170.0) * 0.10;
-      float bleedStrength = smoothstep(0.12, 0.0, overflow) * (0.78 - cornerFactor * 0.26);
-      float bloomBezelBoost = 1.0 +
-          uBloomEnabled * smoothstep(0.16, 0.82, edgeBleedLuma) * 0.75;
-      float bloomLipBoost = 1.0 +
-          uBloomEnabled * smoothstep(0.10, 0.68, edgeBleedLuma) * 0.45;
-
-      vec3 bezelColor =
-          vec3(0.225, 0.225, 0.215) * verticalShade * depthShade +
-          edgeBleedColor * bezelGlow * bleedStrength * 1.12 * bloomBezelBoost +
-          edgeBleedColor * innerLip * 0.36 * bloomLipBoost +
-          vec3(moldedHighlight) +
-          vec3(grain);
-      fragColor = vec4(bezelColor, 1.0);
-      return;
-    }
-  }
-
-  // Read the base color from the source frame.
-  vec4 centerSample = texture(uTexture, uv);
-
-  // Sample 4-neighborhood (N/S/E/W) around the current pixel.
-  vec3 sampleN = texture(uTexture, uv + vec2(0.0, -uTexel.y)).rgb;
-  vec3 sampleS = texture(uTexture, uv + vec2(0.0, uTexel.y)).rgb;
-  vec3 sampleE = texture(uTexture, uv + vec2(uTexel.x, 0.0)).rgb;
-  vec3 sampleW = texture(uTexture, uv + vec2(-uTexel.x, 0.0)).rgb;
-
-  // Compute local luma range; wider range means a stronger edge.
   float lumaCenter = luma(centerSample.rgb);
   float lumaMin = min(
     lumaCenter,
@@ -104,72 +95,78 @@ void main() {
     lumaCenter,
     max(max(luma(sampleN), luma(sampleS)), max(luma(sampleE), luma(sampleW)))
   );
-
+  float edgeAmount = smoothstep(0.03, 0.18, max(lumaMax - lumaMin, 0.0001));
-  float edgeSpan = max(lumaMax - lumaMin, 0.0001);
-  // Convert raw edge strength into a smooth 0..1 blending amount.
-  float edgeAmount = smoothstep(0.03, 0.18, edgeSpan);
-
-  // Average neighbors and blend toward that average only near edges.
-  // This acts like a lightweight edge-aware anti-aliasing pass.
   vec3 neighborhoodAvg = (sampleN + sampleS + sampleE + sampleW) * 0.25;
+
+  // Blend toward neighborhood average near likely edges.
   vec3 aaColor = mix(centerSample.rgb, neighborhoodAvg, edgeAmount * 0.45);
 
-  // Preserve source alpha and output the anti-aliased color.
+  // --------------------------------------------------------------------------
-  vec3 outColor = aaColor;
+  // 3) CRT scanline/sweep/vignette stack
+  // --------------------------------------------------------------------------
+  float scanlineBand = 0.88 + 0.12 * sin(sampleUv.y * uResolution.y * 3.14159265);
+  float sweepPos = fract(uTime * 0.08);
+  float sweepBand = 1.0 + 0.16 * exp(-pow((sampleUv.y - sweepPos) * 120.0, 2.0));
+  vec2 centeredUv = sampleUv * 2.0 - 1.0;
+  float vignette = smoothstep(1.15, 0.25, length(centeredUv));
+  float centerLift = 1.0 + 0.08 * (1.0 - length(centeredUv));
 
-  if (uEffectsEnabled > 0.5) {
+  vec3 crtColor = aaColor;
-    // Horizontal scanline modulation.
+  crtColor *= scanlineBand * sweepBand * centerLift;
-    float scanlineBand = 0.88 + 0.12 * sin(uv.y * uResolution.y * 3.14159265);
+  crtColor *= mix(0.62, 1.0, vignette);
 
-    // Slow bright line crawling down the screen.
+  // Effects mask decides whether CRT modulation is applied.
-    float sweepPos = fract(uTime * 0.08);
+  vec3 screenColor = mix(aaColor, crtColor, uEffectsEnabled);
-    float sweepBand = 1.0 + 0.16 * exp(-pow((uv.y - sweepPos) * 120.0, 2.0));
 
-    // Slight center brightening and edge falloff (CRT phosphor + lens feel).
+  // --------------------------------------------------------------------------
-    vec2 centeredUv = uv * 2.0 - 1.0;
+  // 4) Bezel shading path (branchless selection)
-    float vignette = smoothstep(1.15, 0.25, length(centeredUv));
+  // --------------------------------------------------------------------------
-    float centerLift = 1.0 + 0.08 * (1.0 - length(centeredUv));
+  // This base variant intentionally does not include bloom calculations.
 
-    outColor *= scanlineBand * sweepBand * centerLift;
+  // edgeDelta is non-zero when warp pushes UV outside source bounds.
-    outColor *= mix(0.62, 1.0, vignette);
+  vec2 edgeDelta = effectiveUv - sampleUv;
-  }
+  float overflow = max(abs(edgeDelta.x), abs(edgeDelta.y));
 
-  if (uBloomEnabled > 0.5) {
+  // Sample inward from clamped border to pull scene tint into bezel.
-    // CRT phosphor bloom: bright areas spread a soft luminance glow.
+  vec2 inwardDir = normalize(-edgeDelta + vec2(1e-6));
-    // Sample a three-ring cross pattern directly from the source texture so
+  vec2 bleedStep = vec2(uTexel.x * 1.6, uTexel.y * 1.6);
-    // the spread is measured in source-texel space and stays resolution-stable.
+  vec2 bleedUv1 = clamp(sampleUv + inwardDir * bleedStep, 0.0, 1.0);
-    vec2 s1 = uTexel * 3.0;
+  vec2 bleedUv2 = clamp(sampleUv + inwardDir * bleedStep * 2.6, 0.0, 1.0);
-    vec2 s2 = uTexel * 7.0;
+  vec2 bleedUv3 = clamp(sampleUv + inwardDir * bleedStep * 4.2, 0.0, 1.0);
-    vec2 s3 = uTexel * 13.0;
+  vec3 edgeBleedColor =
+      texture(uTexture, sampleUv).rgb * 0.52 +
+      texture(uTexture, bleedUv1).rgb * 0.28 +
+      texture(uTexture, bleedUv2).rgb * 0.14 +
+      texture(uTexture, bleedUv3).rgb * 0.06;
 
-    vec3 glow = vec3(0.0);
+  // Aspect-corrected radial metrics for bezel falloff shaping.
-    // Inner ring — weight 1.0 each
+  vec2 aspectScale = vec2(uResolution.x / max(uResolution.y, 1.0), 1.0);
-    glow += texture(uTexture, uv + vec2( s1.x,  0.0)).rgb;
+  float bezelDistance = length(edgeDelta * aspectScale);
-    glow += texture(uTexture, uv + vec2(-s1.x,  0.0)).rgb;
+  vec2 clampedCentered = sampleUv * 2.0 - 1.0;
-    glow += texture(uTexture, uv + vec2( 0.0,   s1.y)).rgb;
+  float cornerFactor = smoothstep(0.60, 1.15, length(clampedCentered));
-    glow += texture(uTexture, uv + vec2( 0.0,  -s1.y)).rgb;
-    // Mid ring — weight 0.5 each
-    glow += texture(uTexture, uv + vec2( s2.x,  0.0)).rgb * 0.5;
-    glow += texture(uTexture, uv + vec2(-s2.x,  0.0)).rgb * 0.5;
-    glow += texture(uTexture, uv + vec2( 0.0,   s2.y)).rgb * 0.5;
-    glow += texture(uTexture, uv + vec2( 0.0,  -s2.y)).rgb * 0.5;
-    // Outer ring — weight 0.25 each
-    glow += texture(uTexture, uv + vec2( s3.x,  0.0)).rgb * 0.25;
-    glow += texture(uTexture, uv + vec2(-s3.x,  0.0)).rgb * 0.25;
-    glow += texture(uTexture, uv + vec2( 0.0,   s3.y)).rgb * 0.25;
-    glow += texture(uTexture, uv + vec2( 0.0,  -s3.y)).rgb * 0.25;
-    // Normalize: 4*1.0 + 4*0.5 + 4*0.25 = 7.0
-    glow /= 7.0;
 
-    // Only bright pixels contribute — gate the bloom contribution on luma.
+  // Shading layers:
-    float glowLuma = luma(glow);
+  // - verticalShade: slight top/bottom tonal variance
-    float bloomStrength = smoothstep(0.18, 0.82, glowLuma);
+  // - depthShade: darkens with overflow depth
+  // - grain: subtle analog texture
+  // - moldedHighlight: narrow inner edge highlight
+  float verticalShade = 0.88 + 0.07 * (1.0 - (FlutterFragCoord().y / uResolution.y));
+  float depthShade = 1.0 - smoothstep(0.0, 0.058, overflow) * 0.34;
+  float grain = sin(FlutterFragCoord().x * 0.21 + FlutterFragCoord().y * 0.11) * 0.006;
+  float moldedHighlight = smoothstep(0.072, 0.0, overflow) * 0.028;
+  float bezelGlow = exp(-bezelDistance * 82.0) * mix(1.0, 0.56, cornerFactor);
+  float innerLip = exp(-bezelDistance * 170.0) * 0.10;
+  float bleedStrength = smoothstep(0.12, 0.0, overflow) * (0.78 - cornerFactor * 0.26);
 
-    // Add bloom additively then apply a gentle Reinhard-style tone-map to
+  vec3 bezelColor =
-    // prevent over-saturation while keeping dark areas clean.
+      vec3(0.225, 0.225, 0.215) * verticalShade * depthShade +
-    outColor = outColor + glow * bloomStrength * 0.42;
+      edgeBleedColor * bezelGlow * bleedStrength * 1.12 +
-    outColor = outColor / (outColor + vec3(0.75)) * 1.75;
+      edgeBleedColor * innerLip * 0.36 +
-  }
+      vec3(moldedHighlight) +
+      vec3(grain);
 
-  fragColor = vec4(outColor, centerSample.a);
+  // Final branchless selection between emissive screen and bezel.
+  vec3 outColor = mix(screenColor, bezelColor, bezelMask);
+  float outAlpha = mix(centerSample.a, 1.0, bezelMask);
+  fragColor = vec4(outColor, outAlpha);
 }

packages/wolf_3d_flutter/shaders/wolf_world_bloom.frag

@@ -0,0 +1,212 @@
+#include <flutter/runtime_effect.glsl>
+
+// ----------------------------------------------------------------------------
+// Bloom Variant (Branchless)
+// ----------------------------------------------------------------------------
+// This shader is the bloom-enabled variant of the Wolf CRT post-process path.
+//
+// Why a separate file instead of one giant toggle-heavy shader?
+// - Dart/CPU side chooses this program only when bloom is enabled.
+// - When bloom is disabled, the renderer uses the base shader variant and
+//   avoids bloom texture taps entirely.
+// - This is a deliberate performance decision: skipping work at pipeline
+//   selection time is usually faster than computing work and masking it out.
+//
+// Why so much branchless math?
+// - GPU fragment execution runs many pixels in lockstep.
+// - Divergent control flow reduces throughput.
+// - We prefer mask-driven selection using mix/step/smoothstep.
+//
+// For Dart developers:
+// - Think of this as vectorized numeric dataflow, not object-oriented logic.
+// - Most values are scalar or vector fields over the whole screen.
+// - We combine fields with interpolation/masks instead of choosing one code
+//   path with direct branching.
+
+// Output surface size in pixels for the current draw call.
+uniform vec2 uResolution;
+// One source texel step in UV space: (1/width, 1/height).
+// This keeps kernel sizes stable across resolutions.
+uniform vec2 uTexel;
+// 1.0 enables CRT warp/scanline stack, 0.0 keeps only base AA stack.
+// Even though this is a boolean concept, it is expressed as float because
+// interpolation and mask blending are native operations in GLSL.
+uniform float uEffectsEnabled;
+// Engine time in seconds used to animate scanline travel.
+uniform float uTime;
+// Source frame produced by the software renderer.
+uniform sampler2D uTexture;
+
+out vec4 fragColor;
+
+// Perceptual brightness approximation for edge and bloom gating.
+// This is Rec.601-style luma weighting.
+float luma(vec3 color) {
+  return dot(color, vec3(0.299, 0.587, 0.114));
+}
+
+// Returns 1.0 when uv is inside [0,1] on both axes, else 0.0.
+// Implemented branchlessly with step() products.
+float uvInsideMask(vec2 uv) {
+  vec2 lower = step(vec2(0.0), uv);
+  vec2 upper = step(uv, vec2(1.0));
+  return lower.x * lower.y * upper.x * upper.y;
+}
+
+void main() {
+  // Normalize destination pixel coordinate into UV space.
+  vec2 uv = FlutterFragCoord().xy / uResolution;
+
+  // --------------------------------------------------------------------------
+  // 1) CRT warp selection (branchless)
+  // --------------------------------------------------------------------------
+  // The centered radius term drives a mild barrel distortion.
+  vec2 centered = uv * 2.0 - 1.0;
+  float radius2 = dot(centered, centered);
+  vec2 warpedUv = centered * (1.0 + radius2 * 0.045) * 0.5 + 0.5;
+
+  // Mix between linear and warped UV with a float mask.
+  // In Dart, this is conceptually: useWarped ? warpedUv : uv.
+  vec2 effectiveUv = mix(uv, warpedUv, uEffectsEnabled);
+
+  // Clamp once to keep all downstream texture fetches in bounds.
+  vec2 sampleUv = clamp(effectiveUv, 0.0, 1.0);
+
+  // 1.0 for screen interior, 0.0 outside.
+  float insideMask = uvInsideMask(effectiveUv);
+  // Bezel contributes only where warped coordinates leave the source screen.
+  float bezelMask = (1.0 - insideMask) * uEffectsEnabled;
+
+  // --------------------------------------------------------------------------
+  // 2) Lightweight edge-aware AA
+  // --------------------------------------------------------------------------
+  // Sample center + cardinal neighbors.
+  vec4 centerSample = texture(uTexture, sampleUv);
+  vec3 sampleN = texture(uTexture, clamp(sampleUv + vec2(0.0, -uTexel.y), 0.0, 1.0)).rgb;
+  vec3 sampleS = texture(uTexture, clamp(sampleUv + vec2(0.0, uTexel.y), 0.0, 1.0)).rgb;
+  vec3 sampleE = texture(uTexture, clamp(sampleUv + vec2(uTexel.x, 0.0), 0.0, 1.0)).rgb;
+  vec3 sampleW = texture(uTexture, clamp(sampleUv + vec2(-uTexel.x, 0.0), 0.0, 1.0)).rgb;
+
+  // Luma span estimates local contrast; high span implies stronger edge.
+  float lumaCenter = luma(centerSample.rgb);
+  float lumaMin = min(
+    lumaCenter,
+    min(min(luma(sampleN), luma(sampleS)), min(luma(sampleE), luma(sampleW)))
+  );
+  float lumaMax = max(
+    lumaCenter,
+    max(max(luma(sampleN), luma(sampleS)), max(luma(sampleE), luma(sampleW)))
+  );
+  float edgeAmount = smoothstep(0.03, 0.18, max(lumaMax - lumaMin, 0.0001));
+  vec3 neighborhoodAvg = (sampleN + sampleS + sampleE + sampleW) * 0.25;
+
+  // Blend toward neighborhood average near likely edges.
+  vec3 aaColor = mix(centerSample.rgb, neighborhoodAvg, edgeAmount * 0.45);
+
+  // --------------------------------------------------------------------------
+  // 3) CRT scanline/sweep/vignette stack
+  // --------------------------------------------------------------------------
+  float scanlineBand = 0.88 + 0.12 * sin(sampleUv.y * uResolution.y * 3.14159265);
+  float sweepPos = fract(uTime * 0.08);
+  float sweepBand = 1.0 + 0.16 * exp(-pow((sampleUv.y - sweepPos) * 120.0, 2.0));
+  vec2 centeredUv = sampleUv * 2.0 - 1.0;
+  float vignette = smoothstep(1.15, 0.25, length(centeredUv));
+  float centerLift = 1.0 + 0.08 * (1.0 - length(centeredUv));
+
+  vec3 crtColor = aaColor;
+  crtColor *= scanlineBand * sweepBand * centerLift;
+  crtColor *= mix(0.62, 1.0, vignette);
+
+  // Effects mask decides whether CRT modulation is applied.
+  vec3 screenColor = mix(aaColor, crtColor, uEffectsEnabled);
+
+  // --------------------------------------------------------------------------
+  // 4) Bloom (enabled by selecting this shader variant)
+  // --------------------------------------------------------------------------
+  // Three cross-shaped rings measured in source texels.
+  vec2 s1 = uTexel * 3.0;
+  vec2 s2 = uTexel * 7.0;
+  vec2 s3 = uTexel * 13.0;
+
+  // Accumulate weighted glow taps.
+  vec3 glow = vec3(0.0);
+  glow += texture(uTexture, clamp(sampleUv + vec2( s1.x,  0.0), 0.0, 1.0)).rgb;
+  glow += texture(uTexture, clamp(sampleUv + vec2(-s1.x,  0.0), 0.0, 1.0)).rgb;
+  glow += texture(uTexture, clamp(sampleUv + vec2( 0.0,   s1.y), 0.0, 1.0)).rgb;
+  glow += texture(uTexture, clamp(sampleUv + vec2( 0.0,  -s1.y), 0.0, 1.0)).rgb;
+  glow += texture(uTexture, clamp(sampleUv + vec2( s2.x,  0.0), 0.0, 1.0)).rgb * 0.5;
+  glow += texture(uTexture, clamp(sampleUv + vec2(-s2.x,  0.0), 0.0, 1.0)).rgb * 0.5;
+  glow += texture(uTexture, clamp(sampleUv + vec2( 0.0,   s2.y), 0.0, 1.0)).rgb * 0.5;
+  glow += texture(uTexture, clamp(sampleUv + vec2( 0.0,  -s2.y), 0.0, 1.0)).rgb * 0.5;
+  glow += texture(uTexture, clamp(sampleUv + vec2( s3.x,  0.0), 0.0, 1.0)).rgb * 0.25;
+  glow += texture(uTexture, clamp(sampleUv + vec2(-s3.x,  0.0), 0.0, 1.0)).rgb * 0.25;
+  glow += texture(uTexture, clamp(sampleUv + vec2( 0.0,   s3.y), 0.0, 1.0)).rgb * 0.25;
+  glow += texture(uTexture, clamp(sampleUv + vec2( 0.0,  -s3.y), 0.0, 1.0)).rgb * 0.25;
+
+  // Normalize sum (4*1.0 + 4*0.5 + 4*0.25 = 7.0).
+  glow /= 7.0;
+
+  // Gate bloom with luma to keep dark areas cleaner.
+  float bloomStrength = smoothstep(0.18, 0.82, luma(glow));
+  screenColor = screenColor + glow * bloomStrength * 0.42;
+
+  // Gentle tone map to roll off highlights.
+  screenColor = screenColor / (screenColor + vec3(0.75)) * 1.75;
+
+  // --------------------------------------------------------------------------
+  // 5) Bezel shading path (branchless selection)
+  // --------------------------------------------------------------------------
+  // edgeDelta is non-zero when warp pushes UV outside source bounds.
+  vec2 edgeDelta = effectiveUv - sampleUv;
+  float overflow = max(abs(edgeDelta.x), abs(edgeDelta.y));
+
+  // Sample inward from clamped border to pull scene tint into bezel.
+  vec2 inwardDir = normalize(-edgeDelta + vec2(1e-6));
+  vec2 bleedStep = vec2(uTexel.x * 1.6, uTexel.y * 1.6);
+  vec2 bleedUv1 = clamp(sampleUv + inwardDir * bleedStep, 0.0, 1.0);
+  vec2 bleedUv2 = clamp(sampleUv + inwardDir * bleedStep * 2.6, 0.0, 1.0);
+  vec2 bleedUv3 = clamp(sampleUv + inwardDir * bleedStep * 4.2, 0.0, 1.0);
+  vec3 edgeBleedColor =
+      texture(uTexture, sampleUv).rgb * 0.52 +
+      texture(uTexture, bleedUv1).rgb * 0.28 +
+      texture(uTexture, bleedUv2).rgb * 0.14 +
+      texture(uTexture, bleedUv3).rgb * 0.06;
+
+  // Bezel luma drives bloom-biased boosts near bright edges.
+  float edgeBleedLuma = luma(edgeBleedColor);
+
+  // Aspect-corrected radial metrics for bezel falloff shaping.
+  vec2 aspectScale = vec2(uResolution.x / max(uResolution.y, 1.0), 1.0);
+  float bezelDistance = length(edgeDelta * aspectScale);
+  vec2 clampedCentered = sampleUv * 2.0 - 1.0;
+  float cornerFactor = smoothstep(0.60, 1.15, length(clampedCentered));
+
+  // Shading layers:
+  // - verticalShade: slight top/bottom tonal variance
+  // - depthShade: darkens with overflow depth
+  // - grain: subtle analog texture
+  // - moldedHighlight: narrow inner edge highlight
+  float verticalShade = 0.88 + 0.07 * (1.0 - (FlutterFragCoord().y / uResolution.y));
+  float depthShade = 1.0 - smoothstep(0.0, 0.058, overflow) * 0.34;
+  float grain = sin(FlutterFragCoord().x * 0.21 + FlutterFragCoord().y * 0.11) * 0.006;
+  float moldedHighlight = smoothstep(0.072, 0.0, overflow) * 0.028;
+  float bezelGlow = exp(-bezelDistance * 82.0) * mix(1.0, 0.56, cornerFactor);
+  float innerLip = exp(-bezelDistance * 170.0) * 0.10;
+  float bleedStrength = smoothstep(0.12, 0.0, overflow) * (0.78 - cornerFactor * 0.26);
+
+  // Bloom variant intentionally boosts bezel bleed near bright scene edges.
+  float bloomBezelBoost = 1.0 + smoothstep(0.16, 0.82, edgeBleedLuma) * 0.75;
+  float bloomLipBoost = 1.0 + smoothstep(0.10, 0.68, edgeBleedLuma) * 0.45;
+
+  vec3 bezelColor =
+      vec3(0.225, 0.225, 0.215) * verticalShade * depthShade +
+      edgeBleedColor * bezelGlow * bleedStrength * 1.12 * bloomBezelBoost +
+      edgeBleedColor * innerLip * 0.36 * bloomLipBoost +
+      vec3(moldedHighlight) +
+      vec3(grain);
+
+  // Final branchless selection between emissive screen and bezel.
+  vec3 outColor = mix(screenColor, bezelColor, bezelMask);
+  float outAlpha = mix(centerSample.a, 1.0, bezelMask);
+  fragColor = vec4(outColor, outAlpha);
+}