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

#include <tessellator.h>

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. More...

Public Member Functions
	Tessellator ()

virtual	~Tessellator ()

VertexBuffer	TessellateConvex (const Path &path, HostBuffer &host_buffer, Scalar tolerance, bool supports_primitive_restart=false, bool supports_triangle_fan=false)
	Given a convex path, create a triangle fan structure. More...

VertexBuffer	GenerateLineStrip (const Path &path, HostBuffer &host_buffer, Scalar tolerance)
	Given a path, create a line strip primitive structure. More...

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

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. More...

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). More...

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. More...

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. More...

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. More...

std::vector< Point > &	GetStrokePointCache ()
	Retrieve a pre-allocated arena of kPointArenaSize points. More...

Static Public Member Functions
static void	TessellateConvexInternal (const Path &path, std::vector< Point > &point_buffer, std::vector< uint16_t > &index_buffer, Scalar tolerance)

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. More...

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

std::unique_ptr< std::vector< uint16_t > >	index_buffer_

std::vector< Point >	stroke_points_
	Used for stroke path generation. More...

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 34 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 81 of file tessellator.h.

Member Enumeration Documentation

◆ Result

enum impeller::Tessellator::Result

strong

Enumerator
kSuccess
kInputError
kTessellationError

Definition at line 73 of file tessellator.h.

                     {
     kSuccess,
     kInputError,
     kTessellationError,
   };

Constructor & Destructor Documentation

◆ Tessellator()

impeller::Tessellator::Tessellator ( )

Definition at line 14 of file tessellator.cc.

     : point_buffer_(std::make_unique<std::vector<Point>>()),
       index_buffer_(std::make_unique<std::vector<uint16_t>>()),
       stroke_points_(kPointArenaSize) {
   point_buffer_->reserve(2048);
   index_buffer_->reserve(2048);
 }

References index_buffer_, and point_buffer_.

◆ ~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 28 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;
 }

References impeller::Path::CreatePolyline(), point_buffer_, and 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 339 of file tessellator.cc.

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

References impeller::ComputeQuadrantDivisions(), and impeller::Matrix::GetMaxBasisLengthXY().

◆ 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 399 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.GetMaxBasisLengthXY() * 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,
                                    });
 }

References impeller::ComputeQuadrantDivisions(), impeller::TRect< T >::GetCenter(), impeller::Matrix::GetMaxBasisLengthXY(), impeller::TRect< T >::GetSize(), impeller::TRect< T >::GetWidth(), and impeller::TRect< T >::IsSquare().

◆ 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 420 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.GetMaxBasisLengthXY() * 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);
   }
 }

References impeller::ComputeQuadrantDivisions(), impeller::TRect< T >::GetHeight(), impeller::TRect< T >::GetLeftTop(), impeller::Matrix::GetMaxBasisLengthXY(), impeller::TRect< T >::GetRightBottom(), impeller::TRect< T >::GetWidth(), impeller::TSize< T >::height, impeller::TSize< T >::MaxDimension(), and impeller::TSize< T >::width.

◆ GenerateLineStrip()

VertexBuffer impeller::Tessellator::GenerateLineStrip	(	const Path &	path,
		HostBuffer &	host_buffer,
		Scalar	tolerance
	)

Given a path, create a line strip primitive structure.

        A line strip is a series of vertices that draws a line
        rendered at a specified width (in our case, always 1.0
        physical pixel) that is tessellated by the rasterizer. See
        also PrimitiveType::kLineStrip.

Parameters

[in]	path	The path to tessellate.
[in]	host_buffer	The host buffer for allocation of vertices/index data.
[in]	tolerance	The tolerance value for conversion of the path to a polyline. This value is often derived from the Matrix::GetMaxBasisLengthXY of the CTM applied to the path for rendering.

Returns: A vertex buffer containing all data from the provided curve.

Definition at line 120 of file tessellator.cc.

                                                               {
   LineStripVertexWriter writer(stroke_points_);
   path.WritePolyline(tolerance, writer);
  
   const auto [arena_length, oversized_length] = writer.GetVertexCount();
  
   if (oversized_length == 0) {
     return VertexBuffer{
         .vertex_buffer =
             host_buffer.Emplace(stroke_points_.data(),
                                 arena_length * sizeof(Point), alignof(Point)),
         .index_buffer = {},
         .vertex_count = arena_length,
         .index_type = IndexType::kNone,
     };
   }
   const std::vector<Point>& oversized_data = writer.GetOversizedBuffer();
   BufferView buffer_view = host_buffer.Emplace(
       /*buffer=*/nullptr,                                 //
       (arena_length + oversized_length) * sizeof(Point),  //
       alignof(Point)                                      //
   );
   memcpy(buffer_view.GetBuffer()->OnGetContents() +
              buffer_view.GetRange().offset,  //
          stroke_points_.data(),              //
          arena_length * sizeof(Point)        //
   );
   memcpy(buffer_view.GetBuffer()->OnGetContents() +
              buffer_view.GetRange().offset + arena_length * sizeof(Point),  //
          oversized_data.data(),                                             //
          oversized_data.size() * sizeof(Point)                              //
   );
   buffer_view.GetBuffer()->Flush(buffer_view.GetRange());
  
   return VertexBuffer{
       .vertex_buffer = buffer_view,
       .index_buffer = {},
       .vertex_count = arena_length + oversized_length,
       .index_type = IndexType::kNone,
   };
 }

References buffer_view, impeller::HostBuffer::Emplace(), impeller::LineStripVertexWriter::GetOversizedBuffer(), impeller::LineStripVertexWriter::GetVertexCount(), impeller::kNone, stroke_points_, impeller::VertexBuffer::vertex_buffer, and impeller::Path::WritePolyline().

◆ GetStrokePointCache()

std::vector< Point > & impeller::Tessellator::GetStrokePointCache ( )

Retrieve a pre-allocated arena of kPointArenaSize points.

Definition at line 24 of file tessellator.cc.

                                                    {
   return stroke_points_;
 }

References stroke_points_.

◆ 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 376 of file tessellator.cc.

                    {
   auto along = p1 - p0;
   auto length = along.GetLength();
   if (length > kEhCloseEnough) {
     auto divisions =
         ComputeQuadrantDivisions(view_transform.GetMaxBasisLengthXY() * 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);
   }
 }

References impeller::ComputeQuadrantDivisions(), impeller::TPoint< T >::GetLength(), impeller::Matrix::GetMaxBasisLengthXY(), and impeller::kEhCloseEnough.

◆ 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 355 of file tessellator.cc.

                        {
   if (half_width > 0) {
     auto divisions = ComputeQuadrantDivisions(
         view_transform.GetMaxBasisLengthXY() * 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);
   }
 }

References impeller::ComputeQuadrantDivisions(), and impeller::Matrix::GetMaxBasisLengthXY().

◆ TessellateConvex()

VertexBuffer impeller::Tessellator::TessellateConvex	(	const Path &	path,
		HostBuffer &	host_buffer,
		Scalar	tolerance,
		bool	supports_primitive_restart = `false`,
		bool	supports_triangle_fan = `false`
	)

Given a convex path, create a triangle fan structure.

Parameters

[in]	path	The path to tessellate.
[in]	host_buffer	The host buffer for allocation of vertices/index data.
[in]	tolerance	The tolerance value for conversion of the path to a polyline. This value is often derived from the Matrix::GetMaxBasisLengthXY of the CTM applied to the path for rendering.

Returns: A vertex buffer containing all data from the provided curve.

Definition at line 40 of file tessellator.cc.

                                                                        {
   if (supports_primitive_restart) {
     // Primitive Restart.
     const auto [point_count, contour_count] = path.CountStorage(tolerance);
     BufferView point_buffer = host_buffer.Emplace(
         nullptr, sizeof(Point) * point_count, alignof(Point));
     BufferView index_buffer = host_buffer.Emplace(
         nullptr, sizeof(uint16_t) * (point_count + contour_count),
         alignof(uint16_t));
  
     if (supports_triangle_fan) {
       FanVertexWriter writer(
           reinterpret_cast<Point*>(point_buffer.GetBuffer()->OnGetContents() +
                                    point_buffer.GetRange().offset),
           reinterpret_cast<uint16_t*>(
               index_buffer.GetBuffer()->OnGetContents() +
               index_buffer.GetRange().offset));
       path.WritePolyline(tolerance, writer);
       point_buffer.GetBuffer()->Flush(point_buffer.GetRange());
       index_buffer.GetBuffer()->Flush(index_buffer.GetRange());
  
       return VertexBuffer{
           .vertex_buffer = std::move(point_buffer),
           .index_buffer = std::move(index_buffer),
           .vertex_count = writer.GetIndexCount(),
           .index_type = IndexType::k16bit,
       };
     } else {
       StripVertexWriter writer(
           reinterpret_cast<Point*>(point_buffer.GetBuffer()->OnGetContents() +
                                    point_buffer.GetRange().offset),
           reinterpret_cast<uint16_t*>(
               index_buffer.GetBuffer()->OnGetContents() +
               index_buffer.GetRange().offset));
       path.WritePolyline(tolerance, writer);
       point_buffer.GetBuffer()->Flush(point_buffer.GetRange());
       index_buffer.GetBuffer()->Flush(index_buffer.GetRange());
  
       return VertexBuffer{
           .vertex_buffer = std::move(point_buffer),
           .index_buffer = std::move(index_buffer),
           .vertex_count = writer.GetIndexCount(),
           .index_type = IndexType::k16bit,
       };
     }
   }
  
   FML_DCHECK(point_buffer_);
   FML_DCHECK(index_buffer_);
   TessellateConvexInternal(path, *point_buffer_, *index_buffer_, tolerance);
  
   if (point_buffer_->empty()) {
     return VertexBuffer{
         .vertex_buffer = {},
         .index_buffer = {},
         .vertex_count = 0u,
         .index_type = IndexType::k16bit,
     };
   }
  
   BufferView vertex_buffer = host_buffer.Emplace(
       point_buffer_->data(), sizeof(Point) * point_buffer_->size(),
       alignof(Point));
  
   BufferView index_buffer = host_buffer.Emplace(
       index_buffer_->data(), sizeof(uint16_t) * index_buffer_->size(),
       alignof(uint16_t));
  
   return VertexBuffer{
       .vertex_buffer = std::move(vertex_buffer),
       .index_buffer = std::move(index_buffer),
       .vertex_count = index_buffer_->size(),
       .index_type = IndexType::k16bit,
   };
 }

References impeller::Path::CountStorage(), impeller::HostBuffer::Emplace(), impeller::DeviceBuffer::Flush(), impeller::BufferView::GetBuffer(), impeller::FanVertexWriter::GetIndexCount(), impeller::StripVertexWriter::GetIndexCount(), impeller::BufferView::GetRange(), index_buffer_, impeller::k16bit, impeller::Range::offset, impeller::DeviceBuffer::OnGetContents(), point_buffer_, TessellateConvexInternal(), impeller::VertexBuffer::vertex_buffer, and impeller::Path::WritePolyline().

◆ TessellateConvexInternal()

void impeller::Tessellator::TessellateConvexInternal	(	const Path &	path,
		std::vector< Point > &	point_buffer,
		std::vector< uint16_t > &	index_buffer,
		Scalar	tolerance
	)

static

Visible for testing.

This method only exists for the ease of benchmarking without using the real allocator needed by the [host_buffer].

Definition at line 164 of file tessellator.cc.

                                                              {
   point_buffer.clear();
   index_buffer.clear();
  
   GLESVertexWriter writer(point_buffer, index_buffer);
  
   path.WritePolyline(tolerance, writer);
 }

References impeller::Path::WritePolyline().

Referenced by impeller::BM_Convex(), TessellateConvex(), and impeller::testing::TEST().

Member Data Documentation

◆ index_buffer_

std::unique_ptr<std::vector<uint16_t> > impeller::Tessellator::index_buffer_

protected

Definition at line 315 of file tessellator.h.

Referenced by TessellateConvex(), and Tessellator().

◆ 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 238 of file tessellator.h.

Referenced by impeller::ComputeQuadrantDivisions(), and impeller::testing::TEST().

◆ point_buffer_

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

protected

Used for polyline generation.

Definition at line 314 of file tessellator.h.

Referenced by CreateTempPolyline(), TessellateConvex(), and Tessellator().

◆ stroke_points_

std::vector<Point> impeller::Tessellator::stroke_points_

protected

Used for stroke path generation.

Definition at line 317 of file tessellator.h.

Referenced by GenerateLineStrip(), and GetStrokePointCache().

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 Member Functions

Static Public Attributes

Protected Attributes

Detailed Description

Member Typedef Documentation

◆ TessellatedVertexProc

Member Enumeration Documentation

◆ Result

Constructor & Destructor Documentation

◆ Tessellator()

◆ ~Tessellator()

Member Function Documentation

◆ CreateTempPolyline()

◆ FilledCircle()

◆ FilledEllipse()

◆ FilledRoundRect()

◆ GenerateLineStrip()

◆ GetStrokePointCache()

◆ RoundCapLine()

◆ StrokedCircle()

◆ TessellateConvex()

◆ TessellateConvexInternal()

Member Data Documentation

◆ index_buffer_

◆ kCircleTolerance

◆ point_buffer_

◆ stroke_points_