GrPathUtils::QuadUVMatrix Class Reference

#include <GrPathUtils.h>

Public Member Functions
	QuadUVMatrix ()
	QuadUVMatrix (const SkPoint controlPts[3])
void	set (const SkPoint controlPts[3])
void	apply (void *vertices, int vertexCount, size_t stride, size_t uvOffset) const

Detailed Description

Definition at line 72 of file GrPathUtils.h.

Constructor & Destructor Documentation

QuadUVMatrix() [1/2]

GrPathUtils::QuadUVMatrix::QuadUVMatrix ( )

inline

Definition at line 74 of file GrPathUtils.h.

{}

QuadUVMatrix() [2/2]

GrPathUtils::QuadUVMatrix::QuadUVMatrix ( const SkPoint  controlPts[3] )

inline

Definition at line 76 of file GrPathUtils.h.

{ this->set(controlPts); }

Member Function Documentation

apply()

void GrPathUtils::QuadUVMatrix::apply ( void *  vertices, int  vertexCount, size_t  stride, size_t  uvOffset  ) const

inline

Applies the matrix to vertex positions to compute UV coords.

vertices is a pointer to the first vertex. vertexCount is the number of vertices. stride is the size of each vertex. uvOffset is the offset of the UV values within each vertex.

Definition at line 87 of file GrPathUtils.h.

                                                                                      {
        intptr_t xyPtr = reinterpret_cast<intptr_t>(vertices);
        intptr_t uvPtr = reinterpret_cast<intptr_t>(vertices) + uvOffset;
        float sx = fM[0];
        float kx = fM[1];
        float tx = fM[2];
        float ky = fM[3];
        float sy = fM[4];
        float ty = fM[5];
        for (int i = 0; i < vertexCount; ++i) {
            const SkPoint* xy = reinterpret_cast<const SkPoint*>(xyPtr);
            SkPoint* uv = reinterpret_cast<SkPoint*>(uvPtr);
            uv->fX = sx * xy->fX + kx * xy->fY + tx;
            uv->fY = ky * xy->fX + sy * xy->fY + ty;
            xyPtr += stride;
            uvPtr += stride;
        }
    }

set()

void GrPathUtils::QuadUVMatrix::set

(

const SkPoint

controlPts[3]

)

Definition at line 138 of file GrPathUtils.cpp.

                                                       {
    // We want M such that M * xy_pt = uv_pt
    // We know M * control_pts = [0  1/2 1]
    //                           [0  0   1]
    //                           [1  1   1]
    // And control_pts = [x0 x1 x2]
    //                   [y0 y1 y2]
    //                   [1  1  1 ]
    // We invert the control pt matrix and post concat to both sides to get M.
    // Using the known form of the control point matrix and the result, we can
    // optimize and improve precision.
 
    double x0 = qPts[0].fX;
    double y0 = qPts[0].fY;
    double x1 = qPts[1].fX;
    double y1 = qPts[1].fY;
    double x2 = qPts[2].fX;
    double y2 = qPts[2].fY;
 
    // pre-calculate some adjugate matrix factors for determinant
    double a2 = x1*y2-x2*y1;
    double a5 = x2*y0-x0*y2;
    double a8 = x0*y1-x1*y0;
    double det = a2 + a5 + a8;
 
    if (!SkIsFinite(det)
        || SkScalarNearlyZero((float)det, SK_ScalarNearlyZero * SK_ScalarNearlyZero)) {
        // The quad is degenerate. Hopefully this is rare. Find the pts that are
        // farthest apart to compute a line (unless it is really a pt).
        SkScalar maxD = SkPointPriv::DistanceToSqd(qPts[0], qPts[1]);
        int maxEdge = 0;
        SkScalar d = SkPointPriv::DistanceToSqd(qPts[1], qPts[2]);
        if (d > maxD) {
            maxD = d;
            maxEdge = 1;
        }
        d = SkPointPriv::DistanceToSqd(qPts[2], qPts[0]);
        if (d > maxD) {
            maxD = d;
            maxEdge = 2;
        }
        // We could have a tolerance here, not sure if it would improve anything
        if (maxD > 0) {
            // Set the matrix to give (u = 0, v = distance_to_line)
            SkVector lineVec = qPts[(maxEdge + 1)%3] - qPts[maxEdge];
            // when looking from the point 0 down the line we want positive
            // distances to be to the left. This matches the non-degenerate
            // case.
            lineVec = SkPointPriv::MakeOrthog(lineVec, SkPointPriv::kLeft_Side);
            // first row
            fM[0] = 0;
            fM[1] = 0;
            fM[2] = 0;
            // second row
            fM[3] = lineVec.fX;
            fM[4] = lineVec.fY;
            fM[5] = -lineVec.dot(qPts[maxEdge]);
        } else {
            // It's a point. It should cover zero area. Just set the matrix such
            // that (u, v) will always be far away from the quad.
            fM[0] = 0; fM[1] = 0; fM[2] = 100.f;
            fM[3] = 0; fM[4] = 0; fM[5] = 100.f;
        }
    } else {
        double scale = 1.0/det;
 
        // compute adjugate matrix
        double a3, a4, a6, a7;
        a3 = y2-y0;
        a4 = x0-x2;
 
        a6 = y0-y1;
        a7 = x1-x0;
 
        // this performs the uv_pts*adjugate(control_pts) multiply,
        // then does the scale by 1/det afterwards to improve precision
        fM[0] = (float)((0.5*a3 + a6)*scale);
        fM[1] = (float)((0.5*a4 + a7)*scale);
        fM[2] = (float)((0.5*a5 + a8)*scale);
        fM[3] = (float)(a6*scale);
        fM[4] = (float)(a7*scale);
        fM[5] = (float)(a8*scale);
    }
}

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

• third_party/skia/src/gpu/ganesh/geometry/GrPathUtils.h
• third_party/skia/src/gpu/ganesh/geometry/GrPathUtils.cpp