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[Impeller] Add direct tesselation of circles for DrawCircle and Round…
… end caps
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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 "flutter/impeller/entity/geometry/circle_tessellator.h" | ||
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| #include "flutter/fml/logging.h" | ||
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| namespace impeller { | ||
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| std::vector<Trig> CircleTessellator::trigs_[MAX_DIVISIONS_ + 1]; | ||
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| size_t CircleTessellator::ComputeQuadrantDivisions(Scalar pixel_radius) { | ||
| // Note: these values are approximated based on the values returned from | ||
| // the decomposition of 4 cubics performed by Path::CreatePolyline. | ||
| if (pixel_radius < 1.0) { | ||
| return 1; | ||
| } | ||
| if (pixel_radius < 2.0) { | ||
| return 2; | ||
| } | ||
| if (pixel_radius < 12.0) { | ||
| return 6; | ||
| } | ||
| if (pixel_radius <= 36.0) { | ||
| return 9; | ||
| } | ||
| pixel_radius /= 4; | ||
| if (pixel_radius > (MAX_DIVISIONS_ - 1)) { | ||
| return MAX_DIVISIONS_; | ||
| } | ||
| return static_cast<int>(ceil(pixel_radius)); | ||
| } | ||
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| const std::vector<Trig>& CircleTessellator::GetTrigForDivisions( | ||
| size_t divisions) { | ||
| FML_DCHECK(divisions > 0 && divisions <= MAX_DIVISIONS_); | ||
| std::vector<Trig>& trigs = trigs_[divisions]; | ||
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| if (trigs.empty()) { | ||
| double angle_scale = kPiOver2 / divisions; | ||
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| trigs.emplace_back(1.0, 0.0); | ||
| for (size_t i = 1; i < divisions; i++) { | ||
| trigs.emplace_back(Radians(i * angle_scale)); | ||
| } | ||
| trigs.emplace_back(0.0, 1.0); | ||
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| FML_DCHECK(trigs.size() == divisions + 1); | ||
| } | ||
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| return trigs; | ||
| } | ||
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| void CircleTessellator::ExtendRelativeQuadrantToAbsoluteCircle( | ||
| std::vector<Point>& points, | ||
| const Point& center) { | ||
| auto quadrant_points = points.size(); | ||
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| // The 1st quadrant points are reversed in order, reflected around | ||
| // the Y axis, and translated to become absolute 2nd quadrant points. | ||
| for (size_t i = 1; i <= quadrant_points; i++) { | ||
| auto point = points[quadrant_points - i]; | ||
| points.emplace_back(center.x + point.x, center.y - point.y); | ||
| } | ||
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| // The 1st quadrant points are reflected around the X & Y axes | ||
| // and translated to become absolute 3rd quadrant points. | ||
| for (size_t i = 0; i < quadrant_points; i++) { | ||
| auto point = points[i]; | ||
| points.emplace_back(center.x - point.x, center.y - point.y); | ||
| } | ||
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| // The 1st quadrant points are reversed in order, reflected around | ||
| // the X axis and translated to become absolute 4th quadrant points. | ||
| // The 1st quadrant points are also translated to the center point as | ||
| // well since this is the last time we will use them. | ||
| for (size_t i = 1; i <= quadrant_points; i++) { | ||
| auto point = points[quadrant_points - i]; | ||
| points.emplace_back(center.x - point.x, center.y + point.y); | ||
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| // This is the last loop where we need the first quadrant to be | ||
| // relative so we convert them to absolute as we go. | ||
| points[quadrant_points - i] = center + point; | ||
| } | ||
| } | ||
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| void CircleTessellator::FillQuadrantTriangles(std::vector<Point>& points, | ||
| const Point& center, | ||
| const Point& start_vector, | ||
| const Point& end_vector) const { | ||
| // We only deal with circles for now | ||
| FML_DCHECK(start_vector.GetLength() - end_vector.GetLength() < | ||
| kEhCloseEnough); | ||
| // And only for perpendicular vectors | ||
| FML_DCHECK(start_vector.Dot(end_vector) < kEhCloseEnough); | ||
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| auto trigs = GetTrigForDivisions(quadrant_divisions_); | ||
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| auto prev = center + (trigs[0].cos * start_vector + // | ||
| trigs[0].sin * end_vector); | ||
| for (size_t i = 1; i < trigs.size(); i++) { | ||
| points.emplace_back(center); | ||
| points.emplace_back(prev); | ||
| prev = center + (trigs[i].cos * start_vector + // | ||
| trigs[i].sin * end_vector); | ||
| points.emplace_back(prev); | ||
| } | ||
| } | ||
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| std::vector<Point> CircleTessellator::GetCircleTriangles(const Point& center, | ||
| Scalar radius) const { | ||
| std::vector<Point> points = std::vector<Point>(); | ||
| const size_t quadrant_points = quadrant_divisions_ * 3; | ||
| points.reserve(quadrant_points * 4); | ||
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| // Start with the quadrant top-center to right-center using coordinates | ||
| // relative to the (0, 0). The coordinates will be made absolute relative | ||
| // to the center during the extend method below. | ||
| FillQuadrantTriangles(points, {}, {0, -radius}, {radius, 0}); | ||
| FML_DCHECK(points.size() == quadrant_points); | ||
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| ExtendRelativeQuadrantToAbsoluteCircle(points, center); | ||
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| FML_DCHECK(points.size() == quadrant_points * 4); | ||
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| return points; | ||
| } | ||
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| } // namespace impeller |
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