feat: Add GLSL effects toggle and enhance shader for CRT-like post-processing

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

packages/wolf_3d_renderer/lib/wolf_3d_glsl_renderer.dart

@@ -11,12 +11,16 @@ import 'package:wolf_3d_renderer/wolf_3d_asset_painter.dart';
 
 /// Displays software-rendered frames through a GLSL post-processing pass.
 class WolfGlslRenderer extends BaseWolfRenderer {
+  /// Whether CRT-like post effects are enabled in the shader pass.
+  final bool effectsEnabled;
+
   /// Callback when shader loading fails and software fallback should be used.
   final VoidCallback? onUnavailable;
 
   /// Creates a GLSL renderer bound to [engine].
   const WolfGlslRenderer({
     required super.engine,
+    this.effectsEnabled = false,
     super.onKeyEvent,
     this.onUnavailable,
     super.key,
@@ -113,6 +117,8 @@ class _WolfGlslRendererState extends BaseWolfRendererState<WolfGlslRenderer> {
           painter: _GlslFramePainter(
             frame: _renderedFrame!,
             shader: _shader!,
+            effectsEnabled: widget.effectsEnabled,
+            elapsedSeconds: widget.engine.timeAliveMs / 1000.0,
           ),
           child: const SizedBox.expand(),
         ),
@@ -152,10 +158,14 @@ class _WolfGlslRendererState extends BaseWolfRendererState<WolfGlslRenderer> {
 class _GlslFramePainter extends CustomPainter {
   final ui.Image frame;
   final ui.FragmentShader shader;
+  final bool effectsEnabled;
+  final double elapsedSeconds;
 
   _GlslFramePainter({
     required this.frame,
     required this.shader,
+    required this.effectsEnabled,
+    required this.elapsedSeconds,
   });
 
   @override
@@ -167,6 +177,8 @@ class _GlslFramePainter extends CustomPainter {
       ..setFloat(1, size.height)
       ..setFloat(2, texelX)
       ..setFloat(3, texelY)
+      ..setFloat(4, effectsEnabled ? 1.0 : 0.0)
+      ..setFloat(5, elapsedSeconds)
       ..setImageSampler(0, frame);
 
     final Paint paint = Paint()
@@ -178,6 +190,9 @@ class _GlslFramePainter extends CustomPainter {
 
   @override
   bool shouldRepaint(covariant _GlslFramePainter oldDelegate) {
-    return oldDelegate.frame != frame || oldDelegate.shader != shader;
+    return oldDelegate.frame != frame ||
+        oldDelegate.shader != shader ||
+        oldDelegate.effectsEnabled != effectsEnabled ||
+        oldDelegate.elapsedSeconds != elapsedSeconds;
   }
 }

packages/wolf_3d_renderer/shaders/wolf_world.frag

@@ -4,6 +4,10 @@
 uniform vec2 uResolution;
 // One source-texel step in UV space: (1/width, 1/height).
 uniform vec2 uTexel;
+// 1.0 enables CRT post-process effects, 0.0 keeps only base AA.
+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;
 
@@ -17,6 +21,30 @@ float luma(vec3 color) {
 void main() {
   // Convert fragment coordinates to normalized UV coordinates.
   vec2 uv = FlutterFragCoord().xy / uResolution;
+
+  if (uEffectsEnabled > 0.5) {
+    // Barrel-like warp to emulate curved CRT glass.
+    vec2 centered = uv * 2.0 - 1.0;
+    float radius2 = dot(centered, centered);
+    centered *= 1.0 + radius2 * 0.045;
+    uv = centered * 0.5 + 0.5;
+
+    // Fill outside warped bounds with a subtle gray plastic TV bezel.
+    if (uv.x < 0.0 || uv.x > 1.0 || uv.y < 0.0 || uv.y > 1.0) {
+      vec2 clampedUv = clamp(uv, 0.0, 1.0);
+      vec2 edgeDelta = abs(uv - clampedUv);
+      float overflow = max(edgeDelta.x, edgeDelta.y);
+
+      float verticalShade = 0.96 + 0.06 * (1.0 - (FlutterFragCoord().y / uResolution.y));
+      float depthShade = 1.0 - smoothstep(0.0, 0.06, overflow) * 0.18;
+      float grain = sin(FlutterFragCoord().x * 0.21 + FlutterFragCoord().y * 0.11) * 0.01;
+
+      vec3 bezelColor = vec3(0.46, 0.46, 0.44) * verticalShade * depthShade + vec3(grain);
+      fragColor = vec4(bezelColor, 1.0);
+      return;
+    }
+  }
+
   // Read the base color from the source frame.
   vec4 centerSample = texture(uTexture, uv);
 
@@ -47,5 +75,24 @@ void main() {
   vec3 aaColor = mix(centerSample.rgb, neighborhoodAvg, edgeAmount * 0.45);
 
   // Preserve source alpha and output the anti-aliased color.
-  fragColor = vec4(aaColor, centerSample.a);
+  vec3 outColor = aaColor;
+
+  if (uEffectsEnabled > 0.5) {
+    // Horizontal scanline modulation.
+    float scanlineBand = 0.88 + 0.12 * sin(uv.y * uResolution.y * 3.14159265);
+
+    // Slow bright line crawling down the screen.
+    float sweepPos = fract(uTime * 0.08);
+    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;
+    float vignette = smoothstep(1.15, 0.25, length(centeredUv));
+    float centerLift = 1.0 + 0.08 * (1.0 - length(centeredUv));
+
+    outColor *= scanlineBand * sweepBand * centerLift;
+    outColor *= mix(0.62, 1.0, vignette);
+  }
+
+  fragColor = vec4(outColor, centerSample.a);
 }