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[Impeller] implement Canvas::DrawLine to tesselate lines directly (fl…
…utter#47846) Impeller implements the DrawLine primitive as DrawPath on a path containing a single line. Benchmarks show that this can cost 30% overhead on apps that use a lot of DrawLine primitives. This PR creates a more direct Entity that can tesselate the geometry of a line directly. The reduced overhead should help with flutter/flutter#138004 The current code will back off to Path rendering for round caps. When the circle geometry work is finished (flutter#47845) we can come back and implement round caps using the code refactored in that PR.
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| Original file line number | Diff line number | Diff line change |
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| // Copyright 2013 The Flutter Authors. All rights reserved. | ||
| // Use of this source code is governed by a BSD-style license that can be | ||
| // found in the LICENSE file. | ||
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| #include "impeller/entity/geometry/line_geometry.h" | ||
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| namespace impeller { | ||
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| LineGeometry::LineGeometry(Point p0, Point p1, Scalar width, Cap cap) | ||
| : p0_(p0), p1_(p1), width_(width), cap_(cap) { | ||
| // Some of the code below is prepared to deal with things like coverage | ||
| // of a line with round caps, but more work is needed to deal with drawing | ||
| // the round end caps | ||
| FML_DCHECK(width >= 0); | ||
| FML_DCHECK(cap != Cap::kRound); | ||
| } | ||
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| LineGeometry::~LineGeometry() = default; | ||
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| bool LineGeometry::ComputeCorners(Point corners[4], | ||
| const Matrix& transform, | ||
| bool extend_endpoints) const { | ||
| auto determinant = transform.GetDeterminant(); | ||
| if (determinant == 0) { | ||
| return false; | ||
| } | ||
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| Scalar min_size = 1.0f / sqrt(std::abs(determinant)); | ||
| Scalar stroke_half_width = std::max(width_, min_size) * 0.5f; | ||
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| Point along = p1_ - p0_; | ||
| Scalar length = along.GetLength(); | ||
| if (length < kEhCloseEnough) { | ||
| if (!extend_endpoints) { | ||
| // We won't enclose any pixels unless the endpoints are extended | ||
| return false; | ||
| } | ||
| along = {stroke_half_width, 0}; | ||
| } else { | ||
| along *= stroke_half_width / length; | ||
| } | ||
| Point across = {along.y, -along.x}; | ||
| corners[0] = p0_ - across; | ||
| corners[1] = p1_ - across; | ||
| corners[2] = p0_ + across; | ||
| corners[3] = p1_ + across; | ||
| if (extend_endpoints) { | ||
| corners[0] -= along; | ||
| corners[1] += along; | ||
| corners[2] -= along; | ||
| corners[3] += along; | ||
| } | ||
| return true; | ||
| } | ||
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| GeometryResult LineGeometry::GetPositionBuffer(const ContentContext& renderer, | ||
| const Entity& entity, | ||
| RenderPass& pass) { | ||
| auto& host_buffer = pass.GetTransientsBuffer(); | ||
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| Point corners[4]; | ||
| if (!ComputeCorners(corners, entity.GetTransformation(), | ||
| cap_ == Cap::kSquare)) { | ||
| return {}; | ||
| } | ||
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| return GeometryResult{ | ||
| .type = PrimitiveType::kTriangleStrip, | ||
| .vertex_buffer = | ||
| { | ||
| .vertex_buffer = host_buffer.Emplace(corners, 8 * sizeof(float), | ||
| alignof(float)), | ||
| .vertex_count = 4, | ||
| .index_type = IndexType::kNone, | ||
| }, | ||
| .transform = Matrix::MakeOrthographic(pass.GetRenderTargetSize()) * | ||
| entity.GetTransformation(), | ||
| .prevent_overdraw = false, | ||
| }; | ||
| } | ||
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| // |Geometry| | ||
| GeometryResult LineGeometry::GetPositionUVBuffer(Rect texture_coverage, | ||
| Matrix effect_transform, | ||
| const ContentContext& renderer, | ||
| const Entity& entity, | ||
| RenderPass& pass) { | ||
| auto& host_buffer = pass.GetTransientsBuffer(); | ||
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| auto uv_transform = | ||
| texture_coverage.GetNormalizingTransform() * effect_transform; | ||
| Point corners[4]; | ||
| if (!ComputeCorners(corners, entity.GetTransformation(), | ||
| cap_ == Cap::kSquare)) { | ||
| return {}; | ||
| } | ||
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| std::vector<Point> data(8); | ||
| for (auto i = 0u, j = 0u; i < 8; i += 2, j++) { | ||
| data[i] = corners[j]; | ||
| data[i + 1] = uv_transform * corners[j]; | ||
| } | ||
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| return GeometryResult{ | ||
| .type = PrimitiveType::kTriangleStrip, | ||
| .vertex_buffer = | ||
| { | ||
| .vertex_buffer = host_buffer.Emplace( | ||
| data.data(), 16 * sizeof(float), alignof(float)), | ||
| .vertex_count = 4, | ||
| .index_type = IndexType::kNone, | ||
| }, | ||
| .transform = Matrix::MakeOrthographic(pass.GetRenderTargetSize()) * | ||
| entity.GetTransformation(), | ||
| .prevent_overdraw = false, | ||
| }; | ||
| } | ||
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| GeometryVertexType LineGeometry::GetVertexType() const { | ||
| return GeometryVertexType::kPosition; | ||
| } | ||
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| std::optional<Rect> LineGeometry::GetCoverage(const Matrix& transform) const { | ||
| Point corners[4]; | ||
| if (!ComputeCorners(corners, transform, cap_ != Cap::kButt)) { | ||
| return {}; | ||
| } | ||
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| for (int i = 0; i < 4; i++) { | ||
| corners[i] = transform * corners[i]; | ||
| } | ||
| return Rect::MakePointBounds(std::begin(corners), std::end(corners)); | ||
| } | ||
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| bool LineGeometry::CoversArea(const Matrix& transform, const Rect& rect) const { | ||
| if (!transform.IsTranslationScaleOnly() || !IsAxisAlignedRect()) { | ||
| return false; | ||
| } | ||
| auto coverage = GetCoverage(transform); | ||
| return coverage.has_value() ? coverage->Contains(rect) : false; | ||
| } | ||
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| bool LineGeometry::IsAxisAlignedRect() const { | ||
| return p0_.x == p1_.x || p0_.y == p1_.y; | ||
| } | ||
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| } // namespace impeller |
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