[Impeller] Fix 1d threadgroup dispatch size, Implement drawPoint geometry computation with compute, fallback to specialized CPU. (#42060)

Compute shader implementation of #41803

I found this to be generally more straightforward, and we can revisit the vertex shader approach with GLES.

Benchmark is pending here: flutter/flutter#126728

Note: rendering behavior is identical even though this is now a single draw call. This is becuase strokes have overdraw prevention enabled by default, while this new contents does not

![image](https://github.com/flutter/engine/assets/8975114/29d84e0d-7be6-426a-b5e3-5226c1953a47)

Author: jonahwilliams

ci/licenses_golden/licenses_flutter

@@ -1295,6 +1295,7 @@ ORIGIN: ../../../flutter/impeller/entity/shaders/gaussian_blur/gaussian_blur_alp
 ORIGIN: ../../../flutter/impeller/entity/shaders/gaussian_blur/gaussian_blur_alpha_nodecal.frag + ../../../flutter/LICENSE
 ORIGIN: ../../../flutter/impeller/entity/shaders/gaussian_blur/gaussian_blur_noalpha_decal.frag + ../../../flutter/LICENSE
 ORIGIN: ../../../flutter/impeller/entity/shaders/gaussian_blur/gaussian_blur_noalpha_nodecal.frag + ../../../flutter/LICENSE
+ORIGIN: ../../../flutter/impeller/entity/shaders/geometry/points.comp + ../../../flutter/LICENSE
 ORIGIN: ../../../flutter/impeller/entity/shaders/glyph_atlas.frag + ../../../flutter/LICENSE
 ORIGIN: ../../../flutter/impeller/entity/shaders/glyph_atlas.vert + ../../../flutter/LICENSE
 ORIGIN: ../../../flutter/impeller/entity/shaders/glyph_atlas_color.frag + ../../../flutter/LICENSE
@@ -3916,6 +3917,7 @@ FILE: ../../../flutter/impeller/entity/shaders/gaussian_blur/gaussian_blur_alpha
 FILE: ../../../flutter/impeller/entity/shaders/gaussian_blur/gaussian_blur_alpha_nodecal.frag
 FILE: ../../../flutter/impeller/entity/shaders/gaussian_blur/gaussian_blur_noalpha_decal.frag
 FILE: ../../../flutter/impeller/entity/shaders/gaussian_blur/gaussian_blur_noalpha_nodecal.frag
+FILE: ../../../flutter/impeller/entity/shaders/geometry/points.comp
 FILE: ../../../flutter/impeller/entity/shaders/glyph_atlas.frag
 FILE: ../../../flutter/impeller/entity/shaders/glyph_atlas.vert
 FILE: ../../../flutter/impeller/entity/shaders/glyph_atlas_color.frag

impeller/aiks/aiks_unittests.cc

@@ -2320,5 +2320,35 @@ TEST_P(AiksTest, CanRenderClippedRuntimeEffects) {
   ASSERT_TRUE(OpenPlaygroundHere(canvas.EndRecordingAsPicture()));
 }
 
+TEST_P(AiksTest, CanDrawPoints) {
+  std::vector<Point> points = {
+      {0, 0},      //
+      {100, 100},  //
+      {100, 0},    //
+      {0, 100},    //
+      {0, 0},      //
+      {48, 48},    //
+      {52, 52},    //
+  };
+  std::vector<PointStyle> caps = {
+      PointStyle::kRound,
+      PointStyle::kSquare,
+  };
+  Paint paint;
+  paint.color = Color::Yellow().WithAlpha(0.5);
+
+  Paint background;
+  background.color = Color::Black();
+
+  Canvas canvas;
+  canvas.DrawPaint(background);
+  canvas.Translate({200, 200});
+  canvas.DrawPoints(points, 10, paint, PointStyle::kRound);
+  canvas.Translate({150, 0});
+  canvas.DrawPoints(points, 10, paint, PointStyle::kSquare);
+
+  ASSERT_TRUE(OpenPlaygroundHere(canvas.EndRecordingAsPicture()));
+}
+
 }  // namespace testing
 }  // namespace impeller

impeller/aiks/canvas.cc

@@ -383,6 +383,25 @@ void Canvas::RestoreClip() {
   GetCurrentPass().AddEntity(entity);
 }
 
+void Canvas::DrawPoints(std::vector<Point> points,
+                        Scalar radius,
+                        const Paint& paint,
+                        PointStyle point_style) {
+  if (radius <= 0) {
+    return;
+  }
+
+  Entity entity;
+  entity.SetTransformation(GetCurrentTransformation());
+  entity.SetStencilDepth(GetStencilDepth());
+  entity.SetBlendMode(paint.blend_mode);
+  entity.SetContents(paint.WithFilters(paint.CreateContentsForGeometry(
+      Geometry::MakePointField(std::move(points), radius,
+                               /*round=*/point_style == PointStyle::kRound))));
+
+  GetCurrentPass().AddEntity(entity);
+}
+
 void Canvas::DrawPicture(Picture picture) {
   if (!picture.pass) {
     return;

impeller/aiks/canvas.h

@@ -37,6 +37,14 @@ struct CanvasStackEntry {
   bool contains_clips = false;
 };
 
+enum class PointStyle {
+  /// @brief Points are drawn as squares.
+  kRound,
+
+  /// @brief Points are drawn as circles.
+  kSquare,
+};
+
 class Canvas {
  public:
   struct DebugOptions {
@@ -100,6 +108,11 @@ class Canvas {
 
   void DrawCircle(Point center, Scalar radius, const Paint& paint);
 
+  void DrawPoints(std::vector<Point>,
+                  Scalar radius,
+                  const Paint& paint,
+                  PointStyle point_style);
+
   void DrawImage(const std::shared_ptr<Image>& image,
                  Point offset,
                  const Paint& paint,

impeller/display_list/dl_dispatcher.cc

@@ -930,16 +930,17 @@ void DlDispatcher::drawPoints(PointMode mode,
   Paint paint = paint_;
   paint.style = Paint::Style::kStroke;
   switch (mode) {
-    case flutter::DlCanvas::PointMode::kPoints:
-      if (paint.stroke_cap == Cap::kButt) {
-        paint.stroke_cap = Cap::kSquare;
+    case flutter::DlCanvas::PointMode::kPoints: {
+      // Cap::kButt is also treated as a square.
+      auto point_style = paint.stroke_cap == Cap::kRound ? PointStyle::kRound
+                                                         : PointStyle::kSquare;
+      auto radius = paint.stroke_width;
+      if (radius > 0) {
+        radius /= 2.0;
       }
-      for (uint32_t i = 0; i < count; i++) {
-        Point p0 = skia_conversions::ToPoint(points[i]);
-        auto path = PathBuilder{}.AddLine(p0, p0).TakePath();
-        canvas_.DrawPath(path, paint);
-      }
-      break;
+      canvas_.DrawPoints(skia_conversions::ToPoints(points, count), radius,
+                         paint, point_style);
+    } break;
     case flutter::DlCanvas::PointMode::kLines:
       for (uint32_t i = 1; i < count; i += 2) {
         Point p0 = skia_conversions::ToPoint(points[i - 1]);

impeller/display_list/skia_conversions.cc

@@ -26,6 +26,14 @@ std::vector<Rect> ToRects(const SkRect tex[], int count) {
   return result;
 }
 
+std::vector<Point> ToPoints(const SkPoint points[], int count) {
+  std::vector<Point> result(count);
+  for (auto i = 0; i < count; i++) {
+    result[i] = ToPoint(points[i]);
+  }
+  return result;
+}
+
 PathBuilder::RoundingRadii ToRoundingRadii(const SkRRect& rrect) {
   using Corner = SkRRect::Corner;
   PathBuilder::RoundingRadii radii;

impeller/display_list/skia_conversions.h

@@ -26,6 +26,8 @@ std::optional<Rect> ToRect(const SkRect* rect);
 
 std::vector<Rect> ToRects(const SkRect tex[], int count);
 
+std::vector<Point> ToPoints(const SkPoint points[], int count);
+
 Point ToPoint(const SkPoint& point);
 
 Color ToColor(const SkColor& color);

impeller/entity/BUILD.gn

@@ -96,6 +96,7 @@ impeller_shaders("modern_entity_shaders") {
     "shaders/linear_gradient_ssbo_fill.frag",
     "shaders/radial_gradient_ssbo_fill.frag",
     "shaders/sweep_gradient_ssbo_fill.frag",
+    "shaders/geometry/points.comp",
   ]
 }
 

impeller/entity/contents/content_context.cc

@@ -11,6 +11,7 @@
 #include "impeller/core/formats.h"
 #include "impeller/entity/entity.h"
 #include "impeller/renderer/command_buffer.h"
+#include "impeller/renderer/pipeline_library.h"
 #include "impeller/renderer/render_pass.h"
 #include "impeller/renderer/render_target.h"
 #include "impeller/tessellator/tessellator.h"
@@ -296,6 +297,13 @@ ContentContext::ContentContext(std::shared_ptr<Context> context)
   porter_duff_blend_pipelines_[{}] =
       CreateDefaultPipeline<PorterDuffBlendPipeline>(*context_);
 
+  if (context_->GetCapabilities()->SupportsCompute()) {
+    auto pipeline_desc =
+        PointsComputeShaderPipeline::MakeDefaultPipelineDescriptor(*context_);
+    point_field_compute_pipelines_ =
+        context_->GetPipelineLibrary()->GetPipeline(pipeline_desc).Get();
+  }
+
   if (solid_fill_pipelines_[{}]->GetDescriptor().has_value()) {
     auto clip_pipeline_descriptor =
         solid_fill_pipelines_[{}]->GetDescriptor().value();

impeller/entity/contents/content_context.h

@@ -39,6 +39,7 @@
 #include "impeller/entity/linear_to_srgb_filter.vert.h"
 #include "impeller/entity/morphology_filter.frag.h"
 #include "impeller/entity/morphology_filter.vert.h"
+#include "impeller/entity/points.comp.h"
 #include "impeller/entity/porter_duff_blend.frag.h"
 #include "impeller/entity/radial_gradient_fill.frag.h"
 #include "impeller/entity/rrect_blur.frag.h"
@@ -275,6 +276,9 @@ using FramebufferBlendSoftLightPipeline =
     RenderPipelineT<FramebufferBlendVertexShader,
                     FramebufferBlendSoftlightFragmentShader>;
 
+/// Geometry Pipelines
+using PointsComputeShaderPipeline = ComputePipelineBuilder<PointsComputeShader>;
+
 /// Pipeline state configuration.
 ///
 /// Each unique combination of these options requires a different pipeline state
@@ -660,6 +664,12 @@ class ContentContext {
     return GetPipeline(framebuffer_blend_softlight_pipelines_, opts);
   }
 
+  std::shared_ptr<Pipeline<ComputePipelineDescriptor>> GetPointComputePipeline()
+      const {
+    FML_DCHECK(GetDeviceCapabilities().SupportsCompute());
+    return point_field_compute_pipelines_;
+  }
+
   std::shared_ptr<Context> GetContext() const;
 
   std::shared_ptr<GlyphAtlasContext> GetGlyphAtlasContext(
@@ -782,6 +792,8 @@ class ContentContext {
       framebuffer_blend_screen_pipelines_;
   mutable Variants<FramebufferBlendSoftLightPipeline>
       framebuffer_blend_softlight_pipelines_;
+  mutable std::shared_ptr<Pipeline<ComputePipelineDescriptor>>
+      point_field_compute_pipelines_;
 
   template <class TypedPipeline>
   std::shared_ptr<Pipeline<PipelineDescriptor>> GetPipeline(

impeller/entity/entity_unittests.cc

@@ -2616,5 +2616,23 @@ TEST_P(EntityTest, TessellateConvex) {
   }
 }
 
+TEST_P(EntityTest, PointFieldGeometryDivisions) {
+  // Square always gives 4 divisions.
+  ASSERT_EQ(PointFieldGeometry::ComputeCircleDivisions(24.0, false), 4u);
+  ASSERT_EQ(PointFieldGeometry::ComputeCircleDivisions(2.0, false), 4u);
+  ASSERT_EQ(PointFieldGeometry::ComputeCircleDivisions(200.0, false), 4u);
+
+  ASSERT_EQ(PointFieldGeometry::ComputeCircleDivisions(0.5, true), 4u);
+  ASSERT_EQ(PointFieldGeometry::ComputeCircleDivisions(1.5, true), 8u);
+  ASSERT_EQ(PointFieldGeometry::ComputeCircleDivisions(5.5, true), 24u);
+  ASSERT_EQ(PointFieldGeometry::ComputeCircleDivisions(12.5, true), 34u);
+  ASSERT_EQ(PointFieldGeometry::ComputeCircleDivisions(22.3, true), 22u);
+  ASSERT_EQ(PointFieldGeometry::ComputeCircleDivisions(40.5, true), 40u);
+  ASSERT_EQ(PointFieldGeometry::ComputeCircleDivisions(100.0, true), 100u);
+  // Caps at 140.
+  ASSERT_EQ(PointFieldGeometry::ComputeCircleDivisions(1000.0, true), 140u);
+  ASSERT_EQ(PointFieldGeometry::ComputeCircleDivisions(20000.0, true), 140u);
+}
+
 }  // namespace testing
 }  // namespace impeller