feat: Implement fizzle fade transition effects for menus and intros, enhancing visual transitions

Signed-off-by: Hans Kokx <hans.d.kokx@gmail.com>
2026-03-23 11:00:48 +01:00
parent a84c677845
commit d63b316f1b
7 changed files with 815 additions and 33 deletions
@@ -3,6 +3,7 @@ import 'dart:math' as math;

 import 'package:arcane_helper_utils/arcane_helper_utils.dart';
 import 'package:wolf_3d_dart/src/menu/menu_manager.dart';
+import 'package:wolf_3d_dart/src/rendering/fizzle_fade.dart';
 import 'package:wolf_3d_dart/wolf_3d_data_types.dart';
 import 'package:wolf_3d_dart/wolf_3d_engine.dart';
 import 'package:wolf_3d_dart/wolf_3d_menu.dart';
@@ -130,6 +131,8 @@ class AsciiRenderer extends CliRendererBackend<dynamic> {

  late List<List<ColoredChar>> _screen;
  late List<List<int>> _scenePixels;
+  List<List<ColoredChar>> _screenScratch = const <List<ColoredChar>>[];
+  List<List<int>> _scenePixelsScratch = const <List<int>>[];
  List<int>? _mainMenuBandFirstColumn;
  String? _lastLoggedThemeName;

@@ -488,7 +491,7 @@ class AsciiRenderer extends CliRendererBackend<dynamic> {
      }

      _drawCenteredMenuFooter();
-      _applyMenuFade(engine.menuManager.transitionAlpha, bgColor);
+      _applyMenuTransition(engine.menuManager, bgColor);
      return;
    }

@@ -538,7 +541,7 @@ class AsciiRenderer extends CliRendererBackend<dynamic> {
      }

      _drawCenteredMenuFooter();
-      _applyMenuFade(engine.menuManager.transitionAlpha, bgColor);
+      _applyMenuTransition(engine.menuManager, bgColor);
      return;
    }

@@ -597,7 +600,7 @@ class AsciiRenderer extends CliRendererBackend<dynamic> {
          );
        }
        _drawCenteredMenuFooter();
-        _applyMenuFade(engine.menuManager.transitionAlpha, bgColor);
+        _applyMenuTransition(engine.menuManager, bgColor);
        return;
      }

@@ -638,7 +641,7 @@ class AsciiRenderer extends CliRendererBackend<dynamic> {
      }

      _drawCenteredMenuFooter();
-      _applyMenuFade(engine.menuManager.transitionAlpha, bgColor);
+      _applyMenuTransition(engine.menuManager, bgColor);
      return;
    }

@@ -742,7 +745,7 @@ class AsciiRenderer extends CliRendererBackend<dynamic> {
      }

      _drawCenteredMenuFooter();
-      _applyMenuFade(engine.menuManager.transitionAlpha, bgColor);
+      _applyMenuTransition(engine.menuManager, bgColor);
      return;
    }

@@ -795,7 +798,7 @@ class AsciiRenderer extends CliRendererBackend<dynamic> {
      }

      _drawCenteredMenuFooter();
-      _applyMenuFade(engine.menuManager.transitionAlpha, bgColor);
+      _applyMenuTransition(engine.menuManager, bgColor);
      return;
    }

@@ -851,7 +854,7 @@ class AsciiRenderer extends CliRendererBackend<dynamic> {
        );
      }
      _drawCenteredMenuFooter();
-      _applyMenuFade(engine.menuManager.transitionAlpha, bgColor);
+      _applyMenuTransition(engine.menuManager, bgColor);
      return;
    }

@@ -878,7 +881,7 @@ class AsciiRenderer extends CliRendererBackend<dynamic> {
    }

    _drawCenteredMenuFooter();
-    _applyMenuFade(engine.menuManager.transitionAlpha, bgColor);
+    _applyMenuTransition(engine.menuManager, bgColor);
  }

  String _gameTitle(GameVersion version) {
@@ -932,10 +935,7 @@ class AsciiRenderer extends CliRendererBackend<dynamic> {
      _blitVgaImageAscii(image, x, y);
    }

-    _applyMenuFade(
-      engine.menuManager.introOverlayAlpha,
-      _rgbToPaletteColor(0x000000),
-    );
+    _applyIntroTransition(engine.menuManager, _rgbToPaletteColor(0x000000));
  }

  void _drawRetailWarningIntro(
@@ -1085,6 +1085,148 @@ class AsciiRenderer extends CliRendererBackend<dynamic> {
    }
  }

+  void _applyMenuTransition(MenuManager menuManager, int coverColor) {
+    switch (menuManager.transitionEffect) {
+      case WolfTransitionEffect.none:
+        return;
+      case WolfTransitionEffect.normalFade:
+        _applyMenuFade(menuManager.transitionAlpha, coverColor);
+        return;
+      case WolfTransitionEffect.fizzleFade:
+        _applyFizzleTransition(
+          phase: menuManager.transitionPhase,
+          progress: menuManager.transitionPhaseProgress,
+          coverColor: coverColor,
+        );
+        return;
+    }
+  }
+
+  void _applyIntroTransition(MenuManager menuManager, int coverColor) {
+    switch (menuManager.introOverlayEffect) {
+      case WolfTransitionEffect.none:
+        return;
+      case WolfTransitionEffect.normalFade:
+        _applyMenuFade(menuManager.introOverlayAlpha, coverColor);
+        return;
+      case WolfTransitionEffect.fizzleFade:
+        _applyFizzleTransition(
+          phase: menuManager.introOverlayPhase,
+          progress: menuManager.introOverlayPhaseProgress,
+          coverColor: coverColor,
+        );
+        return;
+    }
+  }
+
+  void _applyFizzleTransition({
+    required WolfTransitionPhase phase,
+    required double progress,
+    required int coverColor,
+  }) {
+    switch (phase) {
+      case WolfTransitionPhase.idle:
+        return;
+      case WolfTransitionPhase.covering:
+        _applyFizzleCover(progress, coverColor);
+        return;
+      case WolfTransitionPhase.revealing:
+        _applyFizzleReveal(progress, coverColor);
+        return;
+    }
+  }
+
+  void _applyFizzleCover(double progress, int coverColor) {
+    final int coverCount = FizzleFade.revealCountForProgress(progress);
+    if (coverCount <= 0) {
+      return;
+    }
+
+    FizzleFade.forEachCanonicalPixel(coverCount, (int x, int y) {
+      _fillRect320(x, y, 1, 1, coverColor);
+    });
+  }
+
+  void _applyFizzleReveal(double progress, int coverColor) {
+    final int revealCount = FizzleFade.revealCountForProgress(progress);
+    if (revealCount <= 0) {
+      if (_usesTerminalLayout) {
+        _fillTerminalRect(0, 0, width, _terminalPixelHeight, coverColor);
+      } else {
+        _fillRect(0, 0, width, height, ' ', coverColor);
+      }
+      return;
+    }
+    if (revealCount >= FizzleFade.canonicalPixelCount) {
+      return;
+    }
+
+    _captureTransitionScratch();
+    if (_usesTerminalLayout) {
+      _fillTerminalRect(0, 0, width, _terminalPixelHeight, coverColor);
+    } else {
+      _fillRect(0, 0, width, height, ' ', coverColor);
+    }
+
+    FizzleFade.forEachCanonicalPixel(revealCount, (int x, int y) {
+      _copyCanonicalPixelFromScratch(x, y);
+    });
+  }
+
+  void _captureTransitionScratch() {
+    if (_usesTerminalLayout) {
+      _scenePixelsScratch = List<List<int>>.generate(
+        _scenePixels.length,
+        (int y) => List<int>.from(_scenePixels[y]),
+      );
+      return;
+    }
+
+    _screenScratch = List<List<ColoredChar>>.generate(
+      _screen.length,
+      (int y) => List<ColoredChar>.from(_screen[y]),
+    );
+  }
+
+  void _copyCanonicalPixelFromScratch(int x320, int y200) {
+    final double scaleX =
+        (_usesTerminalLayout ? projectionWidth : width) / 320.0;
+    final double scaleY =
+        (_usesTerminalLayout ? _terminalPixelHeight : height) / 200.0;
+    final int offsetX = _usesTerminalLayout ? projectionOffsetX : 0;
+    final int startX = offsetX + (x320 * scaleX).floor();
+    final int endX = offsetX + ((x320 + 1) * scaleX).ceil();
+    final int startY = (y200 * scaleY).floor();
+    final int endY = ((y200 + 1) * scaleY).ceil();
+
+    if (_usesTerminalLayout) {
+      for (int y = startY; y < endY; y++) {
+        if (y < 0 || y >= _terminalPixelHeight) {
+          continue;
+        }
+        for (int x = startX; x < endX; x++) {
+          if (x < 0 || x >= width) {
+            continue;
+          }
+          _scenePixels[y][x] = _scenePixelsScratch[y][x];
+        }
+      }
+      return;
+    }
+
+    for (int y = startY; y < endY; y++) {
+      if (y < 0 || y >= height) {
+        continue;
+      }
+      for (int x = startX; x < endX; x++) {
+        if (x < 0 || x >= width) {
+          continue;
+        }
+        _screen[y][x] = _screenScratch[y][x];
+      }
+    }
+  }
+
  void _applyMenuFade(double alpha, int fadeColor) {
    if (alpha <= 0.0) {
      return;
@@ -0,0 +1,66 @@
+import 'dart:collection';
+
+/// Canonical Wolf3D-style 17-bit Galois LFSR used for Fizzle Fade ordering.
+///
+/// The sequence mirrors the original coordinate extraction strategy:
+/// low 8 bits minus one form `y`, the next 9 bits form `x`, and out-of-bounds
+/// points are skipped. For menu and intro rendering we use the original
+/// canonical 320x200 coordinate space and let renderers scale that to their
+/// output buffer.
+abstract final class FizzleFade {
+  static const int canonicalWidth = 320;
+  static const int canonicalHeight = 200;
+  static const int canonicalPixelCount = canonicalWidth * canonicalHeight;
+  static const int seed = 1;
+  static const int _xorMask = 0x12000;
+  static final List<int> _canonicalSequence = List<int>.unmodifiable(
+    _buildSequence(width: canonicalWidth, height: canonicalHeight),
+  );
+
+  static List<int> get canonicalSequence => _canonicalSequence;
+
+  static int nextState(int state) {
+    final bool lsbSet = (state & 1) != 0;
+    int next = state >> 1;
+    if (lsbSet) {
+      next ^= _xorMask;
+    }
+    return next;
+  }
+
+  static int xForState(int state) => (state >> 8) & 0x1FF;
+
+  static int yForState(int state) => ((state & 0xFF) - 1) & 0xFF;
+
+  static bool isInBounds(int state, {required int width, required int height}) {
+    return xForState(state) < width && yForState(state) < height;
+  }
+
+  static int revealCountForProgress(double progress, {int? pixelCount}) {
+    final int total = pixelCount ?? canonicalPixelCount;
+    return (progress.clamp(0.0, 1.0) * total).round().clamp(0, total);
+  }
+
+  static void forEachCanonicalPixel(
+    int count,
+    void Function(int x, int y) plot,
+  ) {
+    final int limit = count.clamp(0, canonicalPixelCount);
+    for (int i = 0; i < limit; i++) {
+      final int packed = _canonicalSequence[i];
+      plot(packed & 0xFFFF, packed >> 16);
+    }
+  }
+
+  static List<int> _buildSequence({required int width, required int height}) {
+    final List<int> points = <int>[];
+    int state = seed;
+    do {
+      if (isInBounds(state, width: width, height: height)) {
+        points.add((yForState(state) << 16) | xForState(state));
+      }
+      state = nextState(state);
+    } while (state != seed);
+    return UnmodifiableListView<int>(points);
+  }
+}
@@ -8,6 +8,7 @@ import 'dart:typed_data';

 import 'package:wolf_3d_dart/src/input/cli_input.dart';
 import 'package:wolf_3d_dart/src/menu/menu_manager.dart';
+import 'package:wolf_3d_dart/src/rendering/fizzle_fade.dart';
 import 'package:wolf_3d_dart/wolf_3d_data_types.dart';
 import 'package:wolf_3d_dart/wolf_3d_engine.dart';
 import 'package:wolf_3d_dart/wolf_3d_menu.dart';
@@ -36,6 +37,7 @@ class SixelRenderer extends CliRendererBackend<String> {
  static const int _headerHeadingY = 24;

  late Uint8List _screen;
+  Uint8List _transitionScratch = Uint8List(0);
  List<int>? _mainMenuBandFirstColumn;
  int _offsetColumns = 0;
  int _offsetRows = 0;
@@ -435,7 +437,7 @@ class SixelRenderer extends CliRendererBackend<String> {
          scale: 1,
        );
      }
-      _applyMenuFade(engine.menuManager.transitionAlpha, bgColor);
+      _applyMenuTransition(engine.menuManager, bgColor);
      return;
    }

@@ -470,7 +472,7 @@ class SixelRenderer extends CliRendererBackend<String> {
          scale: 1,
        );
      }
-      _applyMenuFade(engine.menuManager.transitionAlpha, bgColor);
+      _applyMenuTransition(engine.menuManager, bgColor);
      return;
    }

@@ -522,7 +524,7 @@ class SixelRenderer extends CliRendererBackend<String> {
          );
        }
      }
-      _applyMenuFade(engine.menuManager.transitionAlpha, bgColor);
+      _applyMenuTransition(engine.menuManager, bgColor);
      return;
    }

@@ -615,7 +617,7 @@ class SixelRenderer extends CliRendererBackend<String> {
          scale: 1,
        );
      }
-      _applyMenuFade(engine.menuManager.transitionAlpha, bgColor);
+      _applyMenuTransition(engine.menuManager, bgColor);
      return;
    }

@@ -662,7 +664,7 @@ class SixelRenderer extends CliRendererBackend<String> {
          scale: 1,
        );
      }
-      _applyMenuFade(engine.menuManager.transitionAlpha, bgColor);
+      _applyMenuTransition(engine.menuManager, bgColor);
      return;
    }

@@ -676,7 +678,7 @@ class SixelRenderer extends CliRendererBackend<String> {
    _fillRect320(28, 70, 264, 82, panelColor);
    if (_useCompactMenuLayout) {
      _drawCompactMenu(selectedDifficultyIndex, headingIndex, panelColor);
-      _applyMenuFade(engine.menuManager.transitionAlpha, bgColor);
+      _applyMenuTransition(engine.menuManager, bgColor);
      return;
    }

@@ -717,7 +719,7 @@ class SixelRenderer extends CliRendererBackend<String> {
      );
    }

-    _applyMenuFade(engine.menuManager.transitionAlpha, bgColor);
+    _applyMenuTransition(engine.menuManager, bgColor);
  }

  void _drawCustomizeMenuHeader(
@@ -816,10 +818,7 @@ class SixelRenderer extends CliRendererBackend<String> {
      _blitVgaImage(image, x, y);
    }

-    _applyMenuFade(
-      engine.menuManager.introOverlayAlpha,
-      _rgbToPaletteIndex(0x000000),
-    );
+    _applyIntroTransition(engine.menuManager, _rgbToPaletteIndex(0x000000));
  }

  void _drawRetailWarningIntro(int backgroundColor) {
@@ -861,6 +860,117 @@ class SixelRenderer extends CliRendererBackend<String> {
    return bestIndex;
  }

+  void _applyMenuTransition(MenuManager menuManager, int coverColor) {
+    switch (menuManager.transitionEffect) {
+      case WolfTransitionEffect.none:
+        return;
+      case WolfTransitionEffect.normalFade:
+        _applyMenuFade(menuManager.transitionAlpha, coverColor);
+        return;
+      case WolfTransitionEffect.fizzleFade:
+        _applyFizzleTransition(
+          phase: menuManager.transitionPhase,
+          progress: menuManager.transitionPhaseProgress,
+          coverColor: coverColor,
+        );
+        return;
+    }
+  }
+
+  void _applyIntroTransition(MenuManager menuManager, int coverColor) {
+    switch (menuManager.introOverlayEffect) {
+      case WolfTransitionEffect.none:
+        return;
+      case WolfTransitionEffect.normalFade:
+        _applyMenuFade(menuManager.introOverlayAlpha, coverColor);
+        return;
+      case WolfTransitionEffect.fizzleFade:
+        _applyFizzleTransition(
+          phase: menuManager.introOverlayPhase,
+          progress: menuManager.introOverlayPhaseProgress,
+          coverColor: coverColor,
+        );
+        return;
+    }
+  }
+
+  void _applyFizzleTransition({
+    required WolfTransitionPhase phase,
+    required double progress,
+    required int coverColor,
+  }) {
+    switch (phase) {
+      case WolfTransitionPhase.idle:
+        return;
+      case WolfTransitionPhase.covering:
+        _applyFizzleCover(progress, coverColor);
+        return;
+      case WolfTransitionPhase.revealing:
+        _applyFizzleReveal(progress, coverColor);
+        return;
+    }
+  }
+
+  void _applyFizzleCover(double progress, int coverColor) {
+    final int coverCount = FizzleFade.revealCountForProgress(progress);
+    if (coverCount <= 0) {
+      return;
+    }
+
+    FizzleFade.forEachCanonicalPixel(coverCount, (int x, int y) {
+      _fillRect320(x, y, 1, 1, coverColor);
+    });
+  }
+
+  void _applyFizzleReveal(double progress, int coverColor) {
+    final int revealCount = FizzleFade.revealCountForProgress(progress);
+    if (revealCount <= 0) {
+      _screen.fillRange(0, _screen.length, coverColor);
+      return;
+    }
+    if (revealCount >= FizzleFade.canonicalPixelCount) {
+      return;
+    }
+
+    _ensureTransitionScratch();
+    _transitionScratch.setAll(0, _screen);
+    _screen.fillRange(0, _screen.length, coverColor);
+
+    FizzleFade.forEachCanonicalPixel(revealCount, (int x, int y) {
+      _copyCanonicalPixelFromScratch(x, y);
+    });
+  }
+
+  void _ensureTransitionScratch() {
+    if (_transitionScratch.length == _screen.length) {
+      return;
+    }
+    _transitionScratch = Uint8List(_screen.length);
+  }
+
+  void _copyCanonicalPixelFromScratch(int x320, int y200) {
+    final double scaleX = width / 320.0;
+    final double scaleY = height / 200.0;
+    final int startX = (x320 * scaleX).floor();
+    final int endX = ((x320 + 1) * scaleX).ceil();
+    final int startY = (y200 * scaleY).floor();
+    final int endY = ((y200 + 1) * scaleY).ceil();
+
+    for (int y = startY; y < endY; y++) {
+      if (y < 0 || y >= height) {
+        continue;
+      }
+      final int rowOffset = y * width;
+      for (int x = startX; x < endX; x++) {
+        if (x < 0 || x >= width) {
+          continue;
+        }
+        final int index = rowOffset + x;
+        _screen[index] = _transitionScratch[index];
+      }
+    }
+  }
+
  void _applyMenuFade(double alpha, int bgColor) {
    if (alpha <= 0.0) {
      return;
@@ -1,6 +1,8 @@
 import 'dart:math' as math;
+import 'dart:typed_data';

 import 'package:wolf_3d_dart/src/menu/menu_manager.dart';
+import 'package:wolf_3d_dart/src/rendering/fizzle_fade.dart';
 import 'package:wolf_3d_dart/src/rendering/menu_font.dart';
 import 'package:wolf_3d_dart/src/rendering/renderer_backend.dart';
 import 'package:wolf_3d_dart/wolf_3d_data_types.dart';
@@ -18,6 +20,7 @@ class SoftwareRenderer extends RendererBackend<FrameBuffer> {
  static const int _headerHeadingY = 24;

  late FrameBuffer _buffer;
+  Uint32List _transitionScratch = Uint32List(0);
  List<int>? _mainMenuBandFirstColumn;

  @override
@@ -233,7 +236,7 @@ class SoftwareRenderer extends RendererBackend<FrameBuffer> {
        break;
    }

-    _applyMenuFade(engine.menuManager.transitionAlpha, bgColor);
+    _applyMenuTransition(engine.menuManager, bgColor);
  }

  void _drawIntroSplash(WolfEngine engine, WolfClassicMenuArt art) {
@@ -275,10 +278,7 @@ class SoftwareRenderer extends RendererBackend<FrameBuffer> {
      }
    }

-    _applyMenuFade(
-      engine.menuManager.introOverlayAlpha,
-      _rgbToFrameColor(0x000000),
-    );
+    _applyIntroTransition(engine.menuManager, _rgbToFrameColor(0x000000));
  }

  void _drawRetailWarningIntro(int backgroundColor) {
@@ -550,7 +550,8 @@ class SoftwareRenderer extends RendererBackend<FrameBuffer> {
        ? 0
        : ((optionEntries.length - 1) * optionsRowStep) + 10;
    final int optionsRowStart =
-        optionsPanelY + ((optionsPanelH - optionsRowsHeight) ~/ 2).clamp(0, 200);
+        optionsPanelY +
+        ((optionsPanelH - optionsRowsHeight) ~/ 2).clamp(0, 200);
    for (int i = 0; i < optionEntries.length; i++) {
      final int optionIndex = modeCount + i;
      final bool isSelected = optionIndex == selectedIndex;
@@ -937,6 +938,40 @@ class SoftwareRenderer extends RendererBackend<FrameBuffer> {
    }
  }

+  void _applyMenuTransition(MenuManager menuManager, int coverColor) {
+    switch (menuManager.transitionEffect) {
+      case WolfTransitionEffect.none:
+        return;
+      case WolfTransitionEffect.normalFade:
+        _applyMenuFade(menuManager.transitionAlpha, coverColor);
+        return;
+      case WolfTransitionEffect.fizzleFade:
+        _applyFizzleTransition(
+          phase: menuManager.transitionPhase,
+          progress: menuManager.transitionPhaseProgress,
+          coverColor: coverColor,
+        );
+        return;
+    }
+  }
+
+  void _applyIntroTransition(MenuManager menuManager, int coverColor) {
+    switch (menuManager.introOverlayEffect) {
+      case WolfTransitionEffect.none:
+        return;
+      case WolfTransitionEffect.normalFade:
+        _applyMenuFade(menuManager.introOverlayAlpha, coverColor);
+        return;
+      case WolfTransitionEffect.fizzleFade:
+        _applyFizzleTransition(
+          phase: menuManager.introOverlayPhase,
+          progress: menuManager.introOverlayPhaseProgress,
+          coverColor: coverColor,
+        );
+        return;
+    }
+  }
+
  void _applyMenuFade(double alpha, int fadeColor) {
    if (alpha <= 0.0) {
      return;
@@ -959,6 +994,81 @@ class SoftwareRenderer extends RendererBackend<FrameBuffer> {
    }
  }

+  void _applyFizzleTransition({
+    required WolfTransitionPhase phase,
+    required double progress,
+    required int coverColor,
+  }) {
+    switch (phase) {
+      case WolfTransitionPhase.idle:
+        return;
+      case WolfTransitionPhase.covering:
+        _applyFizzleCover(progress, coverColor);
+        return;
+      case WolfTransitionPhase.revealing:
+        _applyFizzleReveal(progress, coverColor);
+        return;
+    }
+  }
+
+  void _applyFizzleCover(double progress, int coverColor) {
+    final int coverCount = FizzleFade.revealCountForProgress(progress);
+    if (coverCount <= 0) {
+      return;
+    }
+
+    FizzleFade.forEachCanonicalPixel(coverCount, (int x, int y) {
+      _fillCanonicalRect(x, y, 1, 1, coverColor);
+    });
+  }
+
+  void _applyFizzleReveal(double progress, int coverColor) {
+    final int revealCount = FizzleFade.revealCountForProgress(progress);
+    if (revealCount <= 0) {
+      _buffer.pixels.fillRange(0, _buffer.pixels.length, coverColor);
+      return;
+    }
+    if (revealCount >= FizzleFade.canonicalPixelCount) {
+      return;
+    }
+
+    _ensureTransitionScratch();
+    _transitionScratch.setAll(0, _buffer.pixels);
+    _buffer.pixels.fillRange(0, _buffer.pixels.length, coverColor);
+
+    FizzleFade.forEachCanonicalPixel(revealCount, (int x, int y) {
+      _copyCanonicalPixelFromScratch(x, y);
+    });
+  }
+
+  void _ensureTransitionScratch() {
+    if (_transitionScratch.length == _buffer.pixels.length) {
+      return;
+    }
+    _transitionScratch = Uint32List(_buffer.pixels.length);
+  }
+
+  void _copyCanonicalPixelFromScratch(int startX320, int startY200) {
+    final int startX = (startX320 * _uiScaleX).floor();
+    final int endX = ((startX320 + 1) * _uiScaleX).ceil();
+    final int startY = (startY200 * _uiScaleY).floor();
+    final int endY = ((startY200 + 1) * _uiScaleY).ceil();
+
+    for (int y = startY; y < endY; y++) {
+      if (y < 0 || y >= height) {
+        continue;
+      }
+      final int rowStart = y * width;
+      for (int x = startX; x < endX; x++) {
+        if (x < 0 || x >= width) {
+          continue;
+        }
+        final int index = rowStart + x;
+        _buffer.pixels[index] = _transitionScratch[index];
+      }
+    }
+  }
+
  /// Converts an `RRGGBB` menu color into the framebuffer's packed channel
  /// order (`0xAABBGGRR`) used throughout this renderer.
  int _rgbToFrameColor(int rgb) {