Addressed more of Yegor's comments.

Author: eyebrowsoffire

lib/web_ui/lib/painting.dart

@@ -743,9 +743,19 @@ class Shadow {
 }
 
 abstract class ImageShader implements Shader {
-  factory ImageShader(Image image, TileMode tmx, TileMode tmy, Float64List matrix4, {
+  factory ImageShader(
+    Image image,
+    TileMode tmx,
+    TileMode tmy,
+    Float64List matrix4, {
     FilterQuality? filterQuality,
-  }) => engine.renderer.createImageShader(image, tmx, tmy, matrix4, filterQuality);
+  }) => engine.renderer.createImageShader(
+    image,
+    tmx,
+    tmy,
+    matrix4,
+    filterQuality
+  );
 
   @override
   void dispose();

lib/web_ui/lib/src/engine/canvaskit/image.dart

@@ -62,9 +62,7 @@ void skiaDecodeImageFromPixels(
     }
 
     if (targetWidth != null || targetHeight != null) {
-      if (!validUpscale(allowUpscaling, targetWidth, targetHeight, width, height)) {
-        domWindow.console.warn('Cannot apply targetWidth/targetHeight when allowUpscaling is false.');
-      } else {
+      if (validUpscale(allowUpscaling, targetWidth, targetHeight, width, height)) {
         return callback(scaleImage(skImage, targetWidth, targetHeight));
       }
     }

lib/web_ui/lib/src/engine/skwasm/skwasm_impl/renderer.dart

@@ -301,19 +301,16 @@ class SkwasmRenderer implements Renderer {
     int? targetWidth,
     int? targetHeight,
   ) {
-    if (targetWidth == null && targetHeight == null) {
-      return null;
-    }
     if (targetWidth == width && targetHeight == height) {
       // Not scaled
       return null;
     }
     if (targetWidth == null) {
-      if (targetHeight == height) {
+      if (targetHeight == null || targetHeight == height) {
         // Not scaled.
         return null;
       }
-      targetWidth = (width * targetHeight! / height).round();
+      targetWidth = (width * targetHeight / height).round();
     } else if (targetHeight == null) {
       if (targetWidth == targetWidth) {
         // Not scaled.
@@ -336,16 +333,15 @@ class SkwasmRenderer implements Renderer {
     int? targetHeight,
     bool allowUpscaling = true
   }) {
-    final ui.Size? scaledSize = _scaledSize(
+    ui.Size? scaledSize = _scaledSize(
       width,
       height,
       targetWidth,
       targetHeight
     );
     if (!allowUpscaling && scaledSize != null &&
       (scaledSize.width > width || scaledSize.height > height)) {
-        domWindow.console.warn('Cannot apply targetWidth/targetHeight when allowUpscaling is false.');
-        return;
+        scaledSize = null;
     }
     final SkwasmImage pixelImage = SkwasmImage.fromPixels(
       pixels,

lib/web_ui/lib/src/engine/skwasm/skwasm_impl/shaders.dart

@@ -162,18 +162,30 @@ class SkwasmImageShader extends SkwasmShader implements ui.ImageShader {
     SkwasmImage image,
     ui.TileMode tmx,
     ui.TileMode tmy,
-    Float64List matrix4,
+    Float64List? matrix4,
     ui.FilterQuality? filterQuality,
-  ) => withStackScope((StackScope scope) {
-    final RawMatrix33 localMatrix = scope.convertMatrix4toSkMatrix(matrix4);
-    return SkwasmImageShader._(shaderCreateFromImage(
-      image.handle,
-      tmx.index,
-      tmy.index,
-      (filterQuality ?? ui.FilterQuality.medium).index,
-      localMatrix,
-    ));
-  });
+  ) {
+    if (matrix4 != null) {
+      return withStackScope((StackScope scope) {
+        final RawMatrix33 localMatrix = scope.convertMatrix4toSkMatrix(matrix4);
+        return SkwasmImageShader._(shaderCreateFromImage(
+          image.handle,
+          tmx.index,
+          tmy.index,
+          (filterQuality ?? ui.FilterQuality.medium).index,
+          localMatrix,
+        ));
+      });
+    } else {
+      return SkwasmImageShader._(shaderCreateFromImage(
+        image.handle,
+        tmx.index,
+        tmy.index,
+        (filterQuality ?? ui.FilterQuality.medium).index,
+        nullptr,
+      ));
+    }
+  }
 
   @override
   ShaderHandle handle;
@@ -214,18 +226,22 @@ class SkwasmFragmentProgram implements ui.FragmentProgram {
     );
   }
 
-  RuntimeEffectHandle handle;
-  String name;
-  int floatUniformCount;
-  int childShaderCount;
+  final RuntimeEffectHandle handle;
+  final String name;
+  final int floatUniformCount;
+  final int childShaderCount;
+  bool _isDisposed = false;
 
   @override
   ui.FragmentShader fragmentShader() => SkwasmFragmentShader(this);
 
   int get uniformSize => runtimeEffectGetUniformSize(handle);
 
   void dispose() {
-    runtimeEffectDispose(handle);
+    if (!_isDisposed) {
+      runtimeEffectDispose(handle);
+      _isDisposed = true;
+    }
   }
 }
 
@@ -284,7 +300,7 @@ class SkwasmFragmentShader extends SkwasmShader implements ui.FragmentShader {
       image as SkwasmImage,
       ui.TileMode.clamp,
       ui.TileMode.clamp,
-      toMatrix64(Matrix4.identity().storage),
+      null,
       ui.FilterQuality.none,
     );
     final SkwasmShader? oldShader = _childShaders[index];

lib/web_ui/skwasm/surface.cpp

@@ -8,6 +8,7 @@
 #include <emscripten/html5_webgl.h>
 #include <emscripten/threading.h>
 #include <webgl/webgl1.h>
+#include <cassert>
 #include "export.h"
 #include "third_party/skia/include/core/SkCanvas.h"
 #include "third_party/skia/include/core/SkColorSpace.h"
@@ -51,6 +52,8 @@ class Surface {
 
   // Main thread only
   Surface(const char* canvasID) : _canvasID(canvasID) {
+    assert(emscripten_is_main_browser_thread());
+
     pthread_attr_t attr;
     pthread_attr_init(&attr);
     pthread_attr_setdetachstate(&attr, PTHREAD_CREATE_DETACHED);
@@ -67,20 +70,23 @@ class Surface {
 
   // Main thread only
   void dispose() {
+    assert(emscripten_is_main_browser_thread());
     emscripten_dispatch_to_thread(_thread, EM_FUNC_SIG_VI,
                                   reinterpret_cast<void*>(fDispose), nullptr,
                                   this);
   }
 
   // Main thread only
   void setCanvasSize(int width, int height) {
+    assert(emscripten_is_main_browser_thread());
     emscripten_dispatch_to_thread(_thread, EM_FUNC_SIG_VIII,
                                   reinterpret_cast<void*>(fSetCanvasSize),
                                   nullptr, this, width, height);
   }
 
   // Main thread only
   uint32_t renderPicture(SkPicture* picture) {
+    assert(emscripten_is_main_browser_thread());
     uint32_t callbackId = ++_currentCallbackId;
     picture->ref();
     emscripten_dispatch_to_thread(_thread, EM_FUNC_SIG_VII,
@@ -110,6 +116,7 @@ class Surface {
 
   // Main thread only
   void setCallbackHandler(CallbackHandler* callbackHandler) {
+    assert(emscripten_is_main_browser_thread());
     _callbackHandler = callbackHandler;
   }
 
@@ -244,6 +251,7 @@ class Surface {
 
   // Main thread only
   void _onRenderComplete(uint32_t callbackId) {
+    assert(emscripten_is_main_browser_thread());
     _callbackHandler(callbackId, nullptr);
   }