A utility that generates triangles of the specified fill type given a polyline. This happens on the CPU. More...

#include <tessellator.h>

Inheritance diagram for impeller::Tessellator:

Classes
class	EllipticalVertexGenerator
	The \|VertexGenerator\| implementation common to all shapes that are based on a polygonal representation of an ellipse. More...

class	VertexGenerator
	An object which produces a list of vertices as \|Point\|s that tessellate a previously provided shape and delivers the vertices through a \|TessellatedVertexProc\| callback. More...

Public Types
enum class	Result { kSuccess , kInputError , kTessellationError }

using	TessellatedVertexProc = std::function< void(const Point &p)>
	A callback function for a \|VertexGenerator\| to deliver the vertices it computes as \|Point\| objects.

Public Member Functions
	Tessellator ()

virtual	~Tessellator ()

std::vector< Point >	TessellateConvex (const Path &path, Scalar tolerance)
	Given a convex path, create a triangle fan structure.

Path::Polyline	CreateTempPolyline (const Path &path, Scalar tolerance)
	Create a temporary polyline. Only one per-process can exist at a time.

EllipticalVertexGenerator	FilledCircle (const Matrix &view_transform, const Point &center, Scalar radius)
	Create a \|VertexGenerator\| that can produce vertices for a filled circle of the given radius around the given center with enough polygon sub-divisions to provide reasonable fidelity when viewed under the given view transform.

EllipticalVertexGenerator	StrokedCircle (const Matrix &view_transform, const Point &center, Scalar radius, Scalar half_width)
	Create a \|VertexGenerator\| that can produce vertices for a stroked circle of the given radius and half_width around the given shared center with enough polygon sub-divisions to provide reasonable fidelity when viewed under the given view transform. The outer edge of the stroked circle is generated at (radius + half_width) and the inner edge is generated at (radius - half_width).

EllipticalVertexGenerator	RoundCapLine (const Matrix &view_transform, const Point &p0, const Point &p1, Scalar radius)
	Create a \|VertexGenerator\| that can produce vertices for a line with round end caps of the given radius with enough polygon sub-divisions to provide reasonable fidelity when viewed under the given view transform.

EllipticalVertexGenerator	FilledEllipse (const Matrix &view_transform, const Rect &bounds)
	Create a \|VertexGenerator\| that can produce vertices for a filled ellipse inscribed within the given bounds with enough polygon sub-divisions to provide reasonable fidelity when viewed under the given view transform.

EllipticalVertexGenerator	FilledRoundRect (const Matrix &view_transform, const Rect &bounds, const Size &radii)
	Create a \|VertexGenerator\| that can produce vertices for a filled round rect within the given bounds and corner radii with enough polygon sub-divisions to provide reasonable fidelity when viewed under the given view transform.

Static Public Attributes
static constexpr Scalar	kCircleTolerance = 0.1f
	The pixel tolerance used by the algorighm to determine how many divisions to create for a circle.

Protected Attributes
std::unique_ptr< std::vector< Point > >	point_buffer_
	Used for polyline generation.

Detailed Description

A utility that generates triangles of the specified fill type given a polyline. This happens on the CPU.

Also contains functionality for optimized generation of circles and ellipses.

This object is not thread safe, and its methods must not be called from multiple threads.

Definition at line 29 of file tessellator.h.

Member Typedef Documentation

◆ TessellatedVertexProc

using impeller::Tessellator::TessellatedVertexProc = std::function<void(const Point& p)>

A callback function for a |VertexGenerator| to deliver the vertices it computes as |Point| objects.

Definition at line 76 of file tessellator.h.

Member Enumeration Documentation

◆ Result

enum class impeller::Tessellator::Result

strong

Enumerator
kSuccess
kInputError
kTessellationError

Definition at line 68 of file tessellator.h.

                    {
    kSuccess,
    kInputError,
    kTessellationError,
  };

Constructor & Destructor Documentation

◆ Tessellator()

impeller::Tessellator::Tessellator ( )

Definition at line 9 of file tessellator.cc.

    : point_buffer_(std::make_unique<std::vector<Point>>()) {
  point_buffer_->reserve(2048);
}

◆ ~Tessellator()

impeller::Tessellator::~Tessellator ( )

virtualdefault

Member Function Documentation

◆ CreateTempPolyline()

Path::Polyline impeller::Tessellator::CreateTempPolyline	(	const Path &	path,
		Scalar	tolerance
	)

Create a temporary polyline. Only one per-process can exist at a time.

The tessellator itself is not a thread safe class and should only be used from the raster thread.

Definition at line 16 of file tessellator.cc.

                                                                 {
  FML_DCHECK(point_buffer_);
  point_buffer_->clear();
  auto polyline =
      path.CreatePolyline(tolerance, std::move(point_buffer_),
                          [this](Path::Polyline::PointBufferPtr point_buffer) {
                            point_buffer_ = std::move(point_buffer);
                          });
  return polyline;
}

◆ FilledCircle()

EllipticalVertexGenerator impeller::Tessellator::FilledCircle	(	const Matrix &	view_transform,
		const Point &	center,
		Scalar	radius
	)

Create a |VertexGenerator| that can produce vertices for a filled circle of the given radius around the given center with enough polygon sub-divisions to provide reasonable fidelity when viewed under the given view transform.

Note that the view transform is only used to choose the number of sample points to use per quarter circle and the returned points are not transformed by it, instead they are relative to the coordinate space of the center point.

Definition at line 254 of file tessellator.cc.

                   {
  auto divisions =
      ComputeQuadrantDivisions(view_transform.GetMaxBasisLength() * radius);
  return EllipticalVertexGenerator(Tessellator::GenerateFilledCircle,
                                   GetTrigsForDivisions(divisions),
                                   PrimitiveType::kTriangleStrip, 4,
                                   {
                                       .reference_centers = {center, center},
                                       .radii = {radius, radius},
                                       .half_width = -1.0f,
                                   });
}

◆ FilledEllipse()

EllipticalVertexGenerator impeller::Tessellator::FilledEllipse	(	const Matrix &	view_transform,
		const Rect &	bounds
	)

Create a |VertexGenerator| that can produce vertices for a filled ellipse inscribed within the given bounds with enough polygon sub-divisions to provide reasonable fidelity when viewed under the given view transform.

Note that the view transform is only used to choose the number of sample points to use per quarter circle and the returned points are not transformed by it, instead they are relative to the coordinate space of the bounds.

Definition at line 314 of file tessellator.cc.

                        {
  if (bounds.IsSquare()) {
    return FilledCircle(view_transform, bounds.GetCenter(),
                        bounds.GetWidth() * 0.5f);
  }
  auto max_radius = bounds.GetSize().MaxDimension();
  auto divisions =
      ComputeQuadrantDivisions(view_transform.GetMaxBasisLength() * max_radius);
  auto center = bounds.GetCenter();
  return EllipticalVertexGenerator(Tessellator::GenerateFilledEllipse,
                                   GetTrigsForDivisions(divisions),
                                   PrimitiveType::kTriangleStrip, 4,
                                   {
                                       .reference_centers = {center, center},
                                       .radii = bounds.GetSize() * 0.5f,
                                       .half_width = -1.0f,
                                   });
}

◆ FilledRoundRect()

EllipticalVertexGenerator impeller::Tessellator::FilledRoundRect	(	const Matrix &	view_transform,
		const Rect &	bounds,
		const Size &	radii
	)

Create a |VertexGenerator| that can produce vertices for a filled round rect within the given bounds and corner radii with enough polygon sub-divisions to provide reasonable fidelity when viewed under the given view transform.

Note that the view transform is only used to choose the number of sample points to use per quarter circle and the returned points are not transformed by it, instead they are relative to the coordinate space of the bounds.

Definition at line 335 of file tessellator.cc.

                       {
  if (radii.width * 2 < bounds.GetWidth() ||
      radii.height * 2 < bounds.GetHeight()) {
    auto max_radius = radii.MaxDimension();
    auto divisions = ComputeQuadrantDivisions(
        view_transform.GetMaxBasisLength() * max_radius);
    auto upper_left = bounds.GetLeftTop() + radii;
    auto lower_right = bounds.GetRightBottom() - radii;
    return EllipticalVertexGenerator(Tessellator::GenerateFilledRoundRect,
                                     GetTrigsForDivisions(divisions),
                                     PrimitiveType::kTriangleStrip, 4,
                                     {
                                         .reference_centers =
                                             {
                                                 upper_left,
                                                 lower_right,
                                             },
                                         .radii = radii,
                                         .half_width = -1.0f,
                                     });
  } else {
    return FilledEllipse(view_transform, bounds);
  }
}

◆ RoundCapLine()

EllipticalVertexGenerator impeller::Tessellator::RoundCapLine	(	const Matrix &	view_transform,
		const Point &	p0,
		const Point &	p1,
		Scalar	radius
	)

Create a |VertexGenerator| that can produce vertices for a line with round end caps of the given radius with enough polygon sub-divisions to provide reasonable fidelity when viewed under the given view transform.

Note that the view transform is only used to choose the number of sample points to use per quarter circle and the returned points are not transformed by it, instead they are relative to the coordinate space of the two points.

Definition at line 291 of file tessellator.cc.

                   {
  auto along = p1 - p0;
  auto length = along.GetLength();
  if (length > kEhCloseEnough) {
    auto divisions =
        ComputeQuadrantDivisions(view_transform.GetMaxBasisLength() * radius);
    return EllipticalVertexGenerator(Tessellator::GenerateRoundCapLine,
                                     GetTrigsForDivisions(divisions),
                                     PrimitiveType::kTriangleStrip, 4,
                                     {
                                         .reference_centers = {p0, p1},
                                         .radii = {radius, radius},
                                         .half_width = -1.0f,
                                     });
  } else {
    return FilledCircle(view_transform, p0, radius);
  }
}

◆ StrokedCircle()

EllipticalVertexGenerator impeller::Tessellator::StrokedCircle	(	const Matrix &	view_transform,
		const Point &	center,
		Scalar	radius,
		Scalar	half_width
	)

Create a |VertexGenerator| that can produce vertices for a stroked circle of the given radius and half_width around the given shared center with enough polygon sub-divisions to provide reasonable fidelity when viewed under the given view transform. The outer edge of the stroked circle is generated at (radius + half_width) and the inner edge is generated at (radius - half_width).

Note that the view transform is only used to choose the number of sample points to use per quarter circle and the returned points are not transformed by it, instead they are relative to the coordinate space of the center point.

Definition at line 270 of file tessellator.cc.

                       {
  if (half_width > 0) {
    auto divisions = ComputeQuadrantDivisions(
        view_transform.GetMaxBasisLength() * radius + half_width);
    return EllipticalVertexGenerator(Tessellator::GenerateStrokedCircle,
                                     GetTrigsForDivisions(divisions),
                                     PrimitiveType::kTriangleStrip, 8,
                                     {
                                         .reference_centers = {center, center},
                                         .radii = {radius, radius},
                                         .half_width = half_width,
                                     });
  } else {
    return FilledCircle(view_transform, center, radius);
  }
}

◆ TessellateConvex()

std::vector< Point > impeller::Tessellator::TessellateConvex	(	const Path &	path,
		Scalar	tolerance
	)

Given a convex path, create a triangle fan structure.

Parameters

[in]	path	The path to tessellate.
[in]	tolerance	The tolerance value for conversion of the path to a polyline. This value is often derived from the Matrix::GetMaxBasisLength of the CTM applied to the path for rendering.

Returns: A point vector containing the vertices in triangle strip format.

Definition at line 28 of file tessellator.cc.

                                                                   {
  FML_DCHECK(point_buffer_);
 
  std::vector<Point> output;
  point_buffer_->clear();
  auto polyline =
      path.CreatePolyline(tolerance, std::move(point_buffer_),
                          [this](Path::Polyline::PointBufferPtr point_buffer) {
                            point_buffer_ = std::move(point_buffer);
                          });
  if (polyline.points->size() == 0) {
    return output;
  }
 
  output.reserve(polyline.points->size() +
                 (4 * (polyline.contours.size() - 1)));
  bool previous_contour_odd_points = false;
  for (auto j = 0u; j < polyline.contours.size(); j++) {
    auto [start, end] = polyline.GetContourPointBounds(j);
    auto first_point = polyline.GetPoint(start);
 
    // Some polygons will not self close and an additional triangle
    // must be inserted, others will self close and we need to avoid
    // inserting an extra triangle.
    if (polyline.GetPoint(end - 1) == first_point) {
      end--;
    }
 
    if (j > 0) {
      // Triangle strip break.
      output.emplace_back(output.back());
      output.emplace_back(first_point);
      output.emplace_back(first_point);
 
      // If the contour has an odd number of points, insert an extra point when
      // bridging to the next contour to preserve the correct triangle winding
      // order.
      if (previous_contour_odd_points) {
        output.emplace_back(first_point);
      }
    } else {
      output.emplace_back(first_point);
    }
 
    size_t a = start + 1;
    size_t b = end - 1;
    while (a < b) {
      output.emplace_back(polyline.GetPoint(a));
      output.emplace_back(polyline.GetPoint(b));
      a++;
      b--;
    }
    if (a == b) {
      previous_contour_odd_points = false;
      output.emplace_back(polyline.GetPoint(a));
    } else {
      previous_contour_odd_points = true;
    }
  }
  return output;
}

Member Data Documentation

◆ kCircleTolerance

constexpr Scalar impeller::Tessellator::kCircleTolerance = 0.1f

staticconstexpr

The pixel tolerance used by the algorighm to determine how many divisions to create for a circle.

No point on the polygon of vertices should deviate from the true circle by more than this tolerance.

Definition at line 198 of file tessellator.h.

◆ point_buffer_

std::unique_ptr<std::vector<Point> > impeller::Tessellator::point_buffer_

protected

Used for polyline generation.

Definition at line 271 of file tessellator.h.

The documentation for this class was generated from the following files:

impeller/tessellator/tessellator.h
impeller/tessellator/tessellator.cc

Classes

Public Types

Public Member Functions

Static Public Attributes

Protected Attributes