Improve nine-slice atlas sampling

CHANGELOG.md

@@ -3,7 +3,7 @@
 ## Unreleased
 
 - Added TexturePacker frame, manual source-region, and nine-slice image rendering fields for image-capable nodes.
-- Fixed nine-slice image seams by overlapping destination slices during runtime rendering.
+- Fixed nine-slice image seams by overlapping destination slices and using inset source sampling during runtime rendering.
 - Fixed Runtime alpha inheritance so parent fade commands apply to the full child subtree.
 - Added Runtime text shadow fields for text-capable nodes.
 - Fixed Runtime node color alpha composition so `#AARRGGBB` alpha now multiplies with node/runtime alpha instead of being overwritten.

lib/runtime/rendering/runtime_component.dart

@@ -44,6 +44,7 @@ List<({Rect source, Rect destination})> runtimeNineSliceRects({
   double sliceRight = 0,
   double sliceBottom = 0,
   double destinationOverlap = 0,
+  double sourceInset = 0,
 }) {
   if (source.width <= 0 ||
       source.height <= 0 ||
@@ -88,7 +89,7 @@ List<({Rect source, Rect destination})> runtimeNineSliceRects({
   final parts = <({Rect source, Rect destination})>[];
   for (var y = 0; y < 3; y++) {
     for (var x = 0; x < 3; x++) {
-      final sourcePart = Rect.fromLTRB(
+      final rawSourcePart = Rect.fromLTRB(
         sourceXs[x],
         sourceYs[y],
         sourceXs[x + 1],
@@ -100,12 +101,17 @@ List<({Rect source, Rect destination})> runtimeNineSliceRects({
         destXs[x + 1],
         destYs[y + 1],
       );
-      if (sourcePart.width <= 0 ||
+      if (rawSourcePart.width <= 0 ||
-          sourcePart.height <= 0 ||
+          rawSourcePart.height <= 0 ||
           rawDestPart.width <= 0 ||
           rawDestPart.height <= 0) {
         continue;
       }
+      final sourcePart = _insetNineSliceSourceRect(
+        rawSourcePart,
+        bounds: source,
+        inset: sourceInset,
+      );
       final destPart = _overlapNineSliceDestinationRect(
         rawDestPart,
         x: x,
@@ -119,6 +125,22 @@ List<({Rect source, Rect destination})> runtimeNineSliceRects({
   return parts;
 }
 
+Rect _insetNineSliceSourceRect(
+  Rect rect, {
+  required Rect bounds,
+  required double inset,
+}) {
+  if (inset <= 0 || rect.width <= inset * 2 || rect.height <= inset * 2) {
+    return rect;
+  }
+  return Rect.fromLTRB(
+    math.min(rect.right, math.max(bounds.left, rect.left + inset)),
+    math.min(rect.bottom, math.max(bounds.top, rect.top + inset)),
+    math.max(rect.left, math.min(bounds.right, rect.right - inset)),
+    math.max(rect.top, math.min(bounds.bottom, rect.bottom - inset)),
+  );
+}
+
 Rect _overlapNineSliceDestinationRect(
   Rect rect, {
   required int x,
@@ -575,7 +597,13 @@ class RuntimeComponent extends PositionComponent
         ..color = composeRuntimeColorAlpha(Colors.white, renderAlpha);
       final source = _imageSourceRect(image, _currentImageFrame(_node));
       if (_usesNineSlice(source, rect)) {
-        _drawNineSliceImage(canvas, image, source, rect, imagePaint);
+        _drawNineSliceImage(
+          canvas,
+          image,
+          source,
+          rect,
+          imagePaint..filterQuality = FilterQuality.none,
+        );
       } else {
         canvas.drawImageRect(image, source, rect, imagePaint);
       }
@@ -630,7 +658,8 @@ class RuntimeComponent extends PositionComponent
     final parts = runtimeNineSliceRects(
       source: source,
       destination: destination,
-      destinationOverlap: 0.5,
+      destinationOverlap: 1,
+      sourceInset: 0.5,
       sliceLeft: _node.sliceLeft ?? 0,
       sliceTop: _node.sliceTop ?? 0,
       sliceRight: _node.sliceRight ?? 0,

test/runtime/rendering/runtime_component_test.dart

@@ -284,6 +284,36 @@ void main() {
       expect(parts[4].source, const Rect.fromLTRB(10, 10, 20, 20));
     });
 
+    test('insets nine-slice source rects to avoid atlas edge sampling', () {
+      final parts = runtimeNineSliceRects(
+        source: const Rect.fromLTWH(10, 20, 30, 30),
+        destination: const Rect.fromLTWH(0, 0, 90, 90),
+        sliceLeft: 10,
+        sliceTop: 10,
+        sliceRight: 10,
+        sliceBottom: 10,
+        sourceInset: 0.5,
+      );
+
+      expect(parts.first.source, const Rect.fromLTRB(10.5, 20.5, 19.5, 29.5));
+      expect(parts[4].source, const Rect.fromLTRB(20.5, 30.5, 29.5, 39.5));
+      expect(parts.last.source, const Rect.fromLTRB(30.5, 40.5, 39.5, 49.5));
+    });
+
+    test('keeps tiny nine-slice source rects when inset would collapse them', () {
+      final parts = runtimeNineSliceRects(
+        source: const Rect.fromLTWH(0, 0, 3, 3),
+        destination: const Rect.fromLTWH(0, 0, 30, 30),
+        sliceLeft: 1,
+        sliceTop: 1,
+        sliceRight: 1,
+        sliceBottom: 1,
+        sourceInset: 0.5,
+      );
+
+      expect(parts[4].source, const Rect.fromLTRB(1, 1, 2, 2));
+    });
+
     test('updates text alpha style without rebuilding text component', () {
       final component = RuntimeComponent(
         node: const RuntimeNode(