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* Copyright 2019 Google LLC
* Use of this source code is governed by a BSD-style license that can be
* found in the LICENSE file.
#ifndef GrQuadUtils_DEFINED
#define GrQuadUtils_DEFINED
#include "include/private/SkVx.h"
#include "src/gpu/geometry/GrQuad.h"
enum class GrQuadAAFlags;
enum class GrAA : bool;
enum class GrAAType : unsigned;
struct SkRect;
namespace GrQuadUtils {
// Resolve disagreements between the overall requested AA type and the per-edge quad AA flags.
// Both outAAType and outEdgeFlags will be updated.
void ResolveAAType(GrAAType requestedAAType, GrQuadAAFlags requestedEdgeFlags,
const GrQuad& quad, GrAAType* outAAtype, GrQuadAAFlags* outEdgeFlags);
* Clip the device vertices of 'quad' to be in front of the W = 0 plane (w/in epsilon). The
* local coordinates will be updated to match the new clipped vertices. This returns the number
* of clipped quads that need to be drawn: 0 if 'quad' was entirely behind the plane, 1 if
* 'quad' did not need to be clipped or if 2 or 3 vertices were clipped, or 2 if 'quad' had one
* vertex clipped (producing a pentagonal shape spanned by 'quad' and 'extraVertices').
int ClipToW0(DrawQuad* quad, DrawQuad* extraVertices);
* Crops quad to the provided device-space axis-aligned rectangle. If the intersection of this
* quad (projected) and cropRect results in a quadrilateral, this returns true. If not, this
* quad may be updated to be a smaller quad of the same type such that its intersection with
* cropRect is visually the same. This function assumes that the 'quad' coordinates are finite.
* The provided edge flags are updated to reflect edges clipped by cropRect (toggling on or off
* based on cropAA policy). If provided, the local coordinates will be updated to reflect the
* updated device coordinates of this quad.
* If 'computeLocal' is false, the local coordinates in 'quad' will not be modified.
bool CropToRect(const SkRect& cropRect, GrAA cropAA, DrawQuad* quad, bool computeLocal=true);
inline void Outset(const skvx::Vec<4, float>& edgeDistances, GrQuad* quad);
bool WillUseHairline(const GrQuad& quad, GrAAType aaType, GrQuadAAFlags edgeFlags);
class TessellationHelper {
// Set the original device and (optional) local coordinates that are inset or outset
// by the requested edge distances. Use nullptr if there are no local coordinates to update.
// This assumes all device coordinates have been clipped to W > 0.
void reset(const GrQuad& deviceQuad, const GrQuad* localQuad);
// Calculates a new quadrilateral with edges parallel to the original except that they
// have been moved inwards by edgeDistances (which should be positive). Distances are
// ordered L, B, T, R to match CCW tristrip ordering of GrQuad vertices. Edges that are
// not moved (i.e. distance == 0) will not be used in calculations and the corners will
// remain on that edge.
// The per-vertex coverage will be returned. When the inset geometry does not collapse to
// a point or line, this will be 1.0 for every vertex. When it does collapse, the per-vertex
// coverages represent estimated pixel coverage to simulate drawing the subpixel-sized
// original quad.
// Note: the edge distances are in device pixel units, so after rendering the new quad
// edge's shortest distance to the original quad's edge would be equal to provided edge dist
skvx::Vec<4, float> inset(const skvx::Vec<4, float>& edgeDistances,
GrQuad* deviceInset, GrQuad* localInset);
// Calculates a new quadrilateral that outsets the original edges by the given distances.
// Other than moving edges outwards, this function is equivalent to inset(). If the exact
// same edge distances are provided, certain internal computations can be reused across
// consecutive calls to inset() and outset() (in any order).
void outset(const skvx::Vec<4, float>& edgeDistances,
GrQuad* deviceOutset, GrQuad* localOutset);
// Compute the edge equations of the original device space quad passed to 'reset()'. The
// coefficients are stored per-edge in 'a', 'b', and 'c', such that ax + by + c = 0, and
// a positive distance indicates the interior of the quad. Edges are ordered L, B, T, R,
// matching edge distances passed to inset() and outset().
void getEdgeEquations(skvx::Vec<4, float>* a,
skvx::Vec<4, float>* b,
skvx::Vec<4, float>* c);
// Compute the edge lengths of the original device space quad passed to 'reset()'. The
// edge lengths are ordered LBTR to match distances passed to inset() and outset().
skvx::Vec<4, float> getEdgeLengths();
// Determine if the original device space quad has vertices closer than 1px to its opposing
// edges, without going through the full work of computing the insets (assuming that the
// inset distances would be 0.5px).
bool isSubpixel();
// NOTE: This struct is named 'EdgeVectors' because it holds a lot of cached calculations
// pertaining to the edge vectors of the input quad, projected into 2D device coordinates.
// While they are not direction vectors, this struct represents a convenient storage space
// for the projected corners of the quad.
struct EdgeVectors {
// Projected corners (x/w and y/w); these are the 2D coordinates that determine the
// actual edge direction vectors, dx, dy, and invLengths
skvx::Vec<4, float> fX2D, fY2D;
// Normalized edge vectors of the device space quad, ordered L, B, T, R
// (i.e. next_ccw(x) - x).
skvx::Vec<4, float> fDX, fDY;
// Reciprocal of edge length of the device space quad, i.e. 1 / sqrt(dx*dx + dy*dy)
skvx::Vec<4, float> fInvLengths;
// Theta represents the angle formed by the two edges connected at each corner.
skvx::Vec<4, float> fCosTheta;
skvx::Vec<4, float> fInvSinTheta; // 1 / sin(theta)
void reset(const skvx::Vec<4, float>& xs, const skvx::Vec<4, float>& ys,
const skvx::Vec<4, float>& ws, GrQuad::Type quadType);
struct EdgeEquations {
// a * x + b * y + c = 0; positive distance is inside the quad; ordered LBTR.
skvx::Vec<4, float> fA, fB, fC;
void reset(const EdgeVectors& edgeVectors);
skvx::Vec<4, float> estimateCoverage(const skvx::Vec<4, float>& x2d,
const skvx::Vec<4, float>& y2d) const;
bool isSubpixel(const skvx::Vec<4, float>& x2d, const skvx::Vec<4, float>& y2d) const;
// Outsets or insets 'x2d' and 'y2d' in place. To be used when the interior is very
// small, edges are near parallel, or edges are very short/zero-length. Returns number
// of effective vertices in the degenerate quad.
int computeDegenerateQuad(const skvx::Vec<4, float>& signedEdgeDistances,
skvx::Vec<4, float>* x2d, skvx::Vec<4, float>* y2d,
skvx::Vec<4, int32_t>* aaMask) const;
struct OutsetRequest {
// Positive edge distances to move each edge of the quad. These distances represent the
// shortest (perpendicular) distance between the original edge and the inset or outset
// edge. If the distance is 0, then the edge will not move.
skvx::Vec<4, float> fEdgeDistances;
// True if the new corners cannot be calculated by simply adding scaled edge vectors.
// The quad may be degenerate because of the original geometry (near colinear edges), or
// be because of the requested edge distances (collapse of inset, etc.)
bool fInsetDegenerate;
bool fOutsetDegenerate;
void reset(const EdgeVectors& edgeVectors, GrQuad::Type quadType,
const skvx::Vec<4, float>& edgeDistances);
struct Vertices {
// X, Y, and W coordinates in device space. If not perspective, w should be set to 1.f
skvx::Vec<4, float> fX, fY, fW;
// U, V, and R coordinates representing local quad.
// Ignored depending on uvrCount (0, 1, 2).
skvx::Vec<4, float> fU, fV, fR;
int fUVRCount;
void reset(const GrQuad& deviceQuad, const GrQuad* localQuad);
void asGrQuads(GrQuad* deviceOut, GrQuad::Type deviceType,
GrQuad* localOut, GrQuad::Type localType) const;
// Update the device and optional local coordinates by moving the corners along their
// edge vectors such that the new edges have moved 'signedEdgeDistances' from their
// original lines. This should only be called if the 'edgeVectors' fInvSinTheta data is
// numerically sound.
void moveAlong(const EdgeVectors& edgeVectors,
const skvx::Vec<4, float>& signedEdgeDistances);
// Update the device coordinates by deriving (x,y,w) that project to (x2d, y2d), with
// optional local coordinates updated to match the new vertices. It is assumed that
// 'mask' was respected when determining (x2d, y2d), but it is used to ensure that only
// unmasked unprojected edge vectors are used when computing device and local coords.
void moveTo(const skvx::Vec<4, float>& x2d,
const skvx::Vec<4, float>& y2d,
const skvx::Vec<4, int32_t>& mask);
Vertices fOriginal;
EdgeVectors fEdgeVectors;
GrQuad::Type fDeviceType;
GrQuad::Type fLocalType;
// Lazily computed as needed; use accessor functions instead of direct access.
OutsetRequest fOutsetRequest;
EdgeEquations fEdgeEquations;
// Validity of Vertices/EdgeVectors (always true after first call to set()).
bool fVerticesValid = false;
// Validity of outset request (true after calling getOutsetRequest() until next set() call
// or next inset/outset() with different edge distances).
bool fOutsetRequestValid = false;
// Validity of edge equations (true after calling getEdgeEquations() until next set() call).
bool fEdgeEquationsValid = false;
// The requested edge distances must be positive so that they can be reused between inset
// and outset calls.
const OutsetRequest& getOutsetRequest(const skvx::Vec<4, float>& edgeDistances);
const EdgeEquations& getEdgeEquations();
// Outsets or insets 'vertices' by the given perpendicular 'signedEdgeDistances' (inset or
// outset is determined implicitly by the sign of the distances).
void adjustVertices(const skvx::Vec<4, float>& signedEdgeDistances, Vertices* vertices);
// Like adjustVertices() but handles empty edges, collapsed quads, numerical issues, and
// returns the number of effective vertices in the adjusted shape.
int adjustDegenerateVertices(const skvx::Vec<4, float>& signedEdgeDistances,
Vertices* vertices);
friend int ClipToW0(DrawQuad*, DrawQuad*); // To reuse Vertices struct
}; // namespace GrQuadUtils
void GrQuadUtils::Outset(const skvx::Vec<4, float>& edgeDistances, GrQuad* quad) {
TessellationHelper outsetter;
outsetter.reset(*quad, nullptr);
outsetter.outset(edgeDistances, quad, nullptr);