[Impeller] Fix incorrect rendering path when duplicated point exists.

[luckysmg]

Playground test case in this patch

Code

TEST_P(DisplayListTest, StrokedPathsDrawCorrectly) {
  auto callback = [&]() {
    flutter::DisplayListBuilder builder;
    builder.setColor(SK_ColorRED);
    builder.setStyle(flutter::DlDrawStyle::kStroke);

    static float stroke_width = 10.0f;
    static int selected_stroke_type = 0;
    static int selected_join_type = 0;
    const char* stroke_types[] = {"Butte", "Round", "Square"};
    const char* join_type[] = {"kMiter", "Round", "kBevel"};

    ImGui::Begin("Controls", nullptr, ImGuiWindowFlags_AlwaysAutoResize);
    ImGui::Combo("Cap", &selected_stroke_type, stroke_types,
                 sizeof(stroke_types) / sizeof(char*));
    ImGui::Combo("Join", &selected_join_type, join_type,
                 sizeof(join_type) / sizeof(char*));
    ImGui::SliderFloat("Stroke Width", &stroke_width, 10.0f, 50.0f);
    ImGui::End();

    flutter::DlStrokeCap cap;
    flutter::DlStrokeJoin join;
    switch (selected_stroke_type) {
      case 0:
        cap = flutter::DlStrokeCap::kButt;
        break;
      case 1:
        cap = flutter::DlStrokeCap::kRound;
        break;
      case 2:
        cap = flutter::DlStrokeCap::kSquare;
        break;
      default:
        cap = flutter::DlStrokeCap::kButt;
        break;
    }
    switch (selected_join_type) {
      case 0:
        join = flutter::DlStrokeJoin::kMiter;
        break;
      case 1:
        join = flutter::DlStrokeJoin::kRound;
        break;
      case 2:
        join = flutter::DlStrokeJoin::kBevel;
        break;
      default:
        join = flutter::DlStrokeJoin::kMiter;
        break;
    }
    builder.setStrokeCap(cap);
    builder.setStrokeJoin(join);
    builder.setStrokeWidth(stroke_width);

    // Make rendering better to watch.
    builder.scale(1.5f, 1.5f);

    // Rectangle
    builder.translate(100, 100);
    builder.drawRect(SkRect::MakeSize({100, 100}));

    // Rounded rectangle
    builder.translate(150, 0);
    builder.drawRRect(SkRRect::MakeRectXY(SkRect::MakeSize({100, 50}), 10, 10));

    // Double rounded rectangle
    builder.translate(150, 0);
    builder.drawDRRect(
        SkRRect::MakeRectXY(SkRect::MakeSize({100, 50}), 10, 10),
        SkRRect::MakeRectXY(SkRect::MakeXYWH(10, 10, 80, 30), 10, 10));

    // Contour with duplicate join points
    {
      builder.translate(150, 0);
      SkPath path;
      path.moveTo(0, 0);
      path.lineTo(0, 0);
      path.lineTo({100, 0});
      path.lineTo({100, 0});
      path.lineTo({100, 100});
      builder.drawPath(path);
    }

    // Contour with duplicate start and end points

    // Line.
    builder.translate(200, 0);
    {
      builder.save();

      SkPath line_path;
      line_path.moveTo(0, 0);
      line_path.moveTo(0, 0);
      line_path.lineTo({0, 0});
      line_path.lineTo({0, 0});
      line_path.lineTo({50, 50});
      line_path.lineTo({50, 50});
      line_path.lineTo({100, 0});
      line_path.lineTo({100, 0});
      builder.drawPath(line_path);

      builder.translate(0, 100);
      builder.drawPath(line_path);

      builder.translate(0, 100);
      SkPath line_path2;
      line_path2.moveTo(0, 0);
      line_path2.lineTo(0, 0);
      line_path2.lineTo(0, 0);
      builder.drawPath(line_path2);

      builder.restore();
    }

    // Cubic.
    builder.translate(150, 0);
    {
      builder.save();

      SkPath cubic_path;
      cubic_path.moveTo({0, 0});
      cubic_path.cubicTo(0, 0, 140.0, 100.0, 140, 20);
      builder.drawPath(cubic_path);

      builder.translate(0, 100);
      SkPath cubic_path2;
      cubic_path2.moveTo({0, 0});
      cubic_path2.cubicTo(0, 0, 0, 0, 150, 150);
      builder.drawPath(cubic_path2);

      builder.translate(0, 100);
      SkPath cubic_path3;
      cubic_path3.moveTo({0, 0});
      cubic_path3.cubicTo(0, 0, 0, 0, 0, 0);
      builder.drawPath(cubic_path3);

      builder.restore();
    }

    // Quad.
    builder.translate(200, 0);
    {
      builder.save();

      SkPath quad_path;
      quad_path.moveTo(0, 0);
      quad_path.moveTo(0, 0);
      quad_path.quadTo({100, 40}, {50, 80});
      builder.drawPath(quad_path);

      builder.translate(0, 150);
      SkPath quad_path2;
      quad_path2.moveTo(0, 0);
      quad_path2.moveTo(0, 0);
      quad_path2.quadTo({0, 0}, {100, 100});
      builder.drawPath(quad_path2);

      builder.translate(0, 100);
      SkPath quad_path3;
      quad_path3.moveTo(0, 0);
      quad_path3.quadTo({0, 0}, {0, 0});
      builder.drawPath(quad_path3);

      builder.restore();
    }
    return builder.Build();
  };
  ASSERT_TRUE(OpenPlaygroundHere(callback));
}

Before:

Before.mp4

After:

After.mp4

Test Recheck CanDrawCapsAndJoins

Test case in flutter/flutter#119964

Pre-launch Checklist

• I read the [Contributor Guide] and followed the process outlined there for submitting PRs.
• I read the [Tree Hygiene] wiki page, which explains my responsibilities.
• I read and followed the [Flutter Style Guide] and the [C++, Objective-C, Java style guides].
• I listed at least one issue that this PR fixes in the description above.
• I added new tests to check the change I am making or feature I am adding, or Hixie said the PR is test-exempt. See [testing the engine] for instructions on writing and running engine tests.
• I updated/added relevant documentation (doc comments with ///).
• I signed the [CLA].
• All existing and new tests are passing.

[chinmaygarde]

cc @dnfield @bdero

[chinmaygarde]

I think this makes sense but @dnfield might have more comments. I'll defer to his review is he is able.

[chinmaygarde]

component_i is unsigned. Is this necessary?

[luckysmg]

My bad. Should all be size_t instead of int. Done ^_^

[dnfield]

This LGTM.

It does make me wonder if we should just silently elide duplicate components.