SkBezierQuad Class Reference

#include <SkBezierCurves.h>

Static Public Member Functions
static SkSpan< const float >	IntersectWithHorizontalLine (SkSpan< const SkPoint > controlPoints, float yIntercept, float intersectionStorage[2])
static SkSpan< const float >	Intersect (double AX, double BX, double CX, double AY, double BY, double CY, double yIntercept, float intersectionStorage[2])

Detailed Description

Definition at line 76 of file SkBezierCurves.h.

Member Function Documentation

Intersect()

SkSpan< const float > SkBezierQuad::Intersect ( double  AX, double  BX, double  CX, double  AY, double  BY, double  CY, double  yIntercept, float  intersectionStorage[2]  )

static

Given AY*t^2 -2*BY*t + CY = 0 and AX*t^2 - 2*BX*t + CX = 0,

Find the t where AY*t^2 - 2*BY*t + CY - y = 0, then return AX*t^2 + - 2*BX*t + CX where t is on [0, 1].

• y - is the height of the line which intersects the quadratic.
• intersectionStorage - is the array to hold the return data pointed to in the span.

Returns a span with the intersections of yIntercept, and the quadratic formed by A, B, and C.

Definition at line 207 of file SkBezierCurves.cpp.

                                                         {
    auto [discriminant, r0, r1] = SkQuads::Roots(AY, BY, CY - yIntercept);
 
    int intersectionCount = 0;
    // Round the roots to the nearest float to generate the values t. Valid t's are on the
    // domain [0, 1].
    const double t0 = pinTRange(r0);
    if (0 <= t0 && t0 <= 1) {
        intersectionStorage[intersectionCount++] = SkQuads::EvalAt(AX, -2 * BX, CX, t0);
    }
 
    const double t1 = pinTRange(r1);
    if (0 <= t1 && t1 <= 1 && t1 != t0) {
        intersectionStorage[intersectionCount++] = SkQuads::EvalAt(AX, -2 * BX, CX, t1);
    }
 
    return SkSpan{intersectionStorage, intersectionCount};
}

IntersectWithHorizontalLine()

SkSpan< const float > SkBezierQuad::IntersectWithHorizontalLine ( SkSpan< const SkPoint >  controlPoints, float  yIntercept, float  intersectionStorage[2]  )

static

Definition at line 189 of file SkBezierCurves.cpp.

                                                                        {
    SkASSERT(controlPoints.size() >= 3);
    const DPoint p0 = controlPoints[0],
                 p1 = controlPoints[1],
                 p2 = controlPoints[2];
 
    // Calculate A, B, C using doubles to reduce round-off error.
    const DPoint A = p0 - 2 * p1 + p2,
    // Remember we are generating the polynomial in the form A*t^2 -2*B*t + C, so the factor
    // of 2 is not needed and the term is negated. This term for a Bézier curve is usually
    // 2(p1-p0).
                 B = p0 - p1,
                 C = p0;
 
    return Intersect(A.x, B.x, C.x, A.y, B.y, C.y, yIntercept, intersectionStorage);
}

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

• third_party/skia/src/base/SkBezierCurves.h
• third_party/skia/src/base/SkBezierCurves.cpp