[Impeller] generate mipmaps for toImage. (#55655)

Fixes flutter/flutter#156161

Mips must be eagerly generated for Picture.toImage and friends so that filter quality (mip sampling) works as expected.

Author: Jonah Williams

impeller/display_list/dl_dispatcher.cc

@@ -1368,7 +1368,12 @@ std::shared_ptr<Texture> DisplayListToTexture(
     const sk_sp<flutter::DisplayList>& display_list,
     ISize size,
     AiksContext& context,
-    bool reset_host_buffer) {
+    bool reset_host_buffer,
+    bool generate_mips) {
+  int mip_count = 1;
+  if (generate_mips) {
+    mip_count = size.MipCount();
+  }
   // Do not use the render target cache as the lifecycle of this texture
   // will outlive a particular frame.
   impeller::RenderTargetAllocator render_target_allocator =
@@ -1379,7 +1384,7 @@ std::shared_ptr<Texture> DisplayListToTexture(
     target = render_target_allocator.CreateOffscreenMSAA(
         *context.GetContext(),  // context
         size,                   // size
-        /*mip_count=*/1,
+        /*mip_count=*/mip_count,
         "Picture Snapshot MSAA",  // label
         impeller::RenderTarget::
             kDefaultColorAttachmentConfigMSAA  // color_attachment_config
@@ -1388,7 +1393,7 @@ std::shared_ptr<Texture> DisplayListToTexture(
     target = render_target_allocator.CreateOffscreen(
         *context.GetContext(),  // context
         size,                   // size
-        /*mip_count=*/1,
+        /*mip_count=*/mip_count,
         "Picture Snapshot",  // label
         impeller::RenderTarget::
             kDefaultColorAttachmentConfig  // color_attachment_config

impeller/display_list/dl_dispatcher.h

@@ -370,7 +370,8 @@ std::shared_ptr<Texture> DisplayListToTexture(
     const sk_sp<flutter::DisplayList>& display_list,
     ISize size,
     AiksContext& context,
-    bool reset_host_buffer = true);
+    bool reset_host_buffer = true,
+    bool generate_mips = false);
 
 /// Render the provided display list to the render target.
 bool RenderToOnscreen(ContentContext& context, RenderTarget render_target,

shell/common/snapshot_controller_impeller.cc

@@ -14,7 +14,6 @@
 #include "flutter/impeller/geometry/size.h"
 #include "flutter/shell/common/snapshot_controller.h"
 #include "impeller/entity/contents/runtime_effect_contents.h"
-#include "impeller/renderer/render_target.h"
 
 namespace flutter {
 
@@ -49,7 +48,8 @@ sk_sp<DlImage> DoMakeRasterSnapshot(
 
   return impeller::DlImageImpeller::Make(
       impeller::DisplayListToTexture(display_list, render_target_size, *context,
-                                     /*reset_host_buffer=*/false),
+                                     /*reset_host_buffer=*/false,
+                                     /*generate_mips=*/true),
       DlImage::OwningContext::kRaster);
 }
 

testing/dart/painting_test.dart

@@ -114,4 +114,41 @@ void main() {
       'ImageFilter.matrix($data, FilterQuality.medium)',
     );
   });
+
+  test('Picture.toImage generates mip maps', () async {
+    // Draw a grid of red and blue squares. When averaged together via
+    // mip maps, this should result in a purplish color. If there are no
+    // mip maps, the original red and blue colors will be preserved regardless
+    // of scale or number of pixels.
+    late final Image image;
+    {
+      final PictureRecorder recorder = PictureRecorder();
+      final Canvas canvas = Canvas(recorder);
+      for (int i = 0; i < 20; i++) {
+        for (int j = 0; j < 20; j++) {
+          final Color color = (i + j).isEven ? const Color(0xFFFF0000) : const Color(0xFF0000FF);
+          canvas.drawRect(Rect.fromLTWH(i * 5, j * 5, 5, 5), Paint()..color = color);
+        }
+      }
+      final Picture picture = recorder.endRecording();
+      image = await picture.toImage(100, 100);
+    }
+
+    final PictureRecorder recorder = PictureRecorder();
+    final Canvas canvas = Canvas(recorder);
+    canvas.save();
+    canvas.scale(0.25, 0.25);
+    canvas.drawImage(image, Offset.zero, Paint()..filterQuality = FilterQuality.medium);
+    canvas.restore();
+
+    final Picture picture = recorder.endRecording();
+    final Image resultImage = await picture.toImage(10, 10);
+    final ByteData data = (await resultImage.toByteData())!;
+
+    final Int32List colors = data.buffer.asInt32List();
+    for (int i = 0; i < colors.length; i++) {
+      expect(colors[i], isNot(const Color(0xFFFF0000)));
+      expect(colors[i], isNot(const Color(0xFF0000FF)));
+    }
+  });
 }