FwDCubicEvaluator Class Reference

Public Member Functions
	FwDCubicEvaluator (const SkPoint points[4])
void	restart (int divisions)
bool	done () const
SkPoint	next ()
const SkPoint *	getCtrlPoints () const

Detailed Description

Evaluator to sample the values of a cubic bezier using forward differences. Forward differences is a method for evaluating a nth degree polynomial at a uniform step by only adding precalculated values. For a linear example we have the function f(t) = m*t+b, then the value of that function at t+h would be f(t+h) = m*(t+h)+b. If we want to know the uniform step that we must add to the first evaluation f(t) then we need to substract f(t+h) - f(t) = m*t + m*h + b - m*t + b = mh. After obtaining this value (mh) we could just add this constant step to our first sampled point to compute the next one.

For the cubic case the first difference gives as a result a quadratic polynomial to which we can apply again forward differences and get linear function to which we can apply again forward differences to get a constant difference. This is why we keep an array of size 4, the 0th position keeps the sampled value while the next ones keep the quadratic, linear and constant difference values.

Definition at line 84 of file SkPatchUtils.cpp.

Constructor & Destructor Documentation

FwDCubicEvaluator()

FwDCubicEvaluator::FwDCubicEvaluator ( const SkPoint  points[4] )

inlineexplicit

Receives the 4 control points of the cubic bezier.

Definition at line 92 of file SkPatchUtils.cpp.

            : fCoefs(points) {
        memcpy(fPoints, points, 4 * sizeof(SkPoint));
 
        this->restart(1);
    }

Member Function Documentation

done()

bool FwDCubicEvaluator::done ( ) const

inline

Check if the evaluator is still within the range of 0<=t<=1

Definition at line 119 of file SkPatchUtils.cpp.

                      {
        return fCurrent > fMax;
    }

getCtrlPoints()

const SkPoint * FwDCubicEvaluator::getCtrlPoints ( ) const

inline

Definition at line 135 of file SkPatchUtils.cpp.

                                         {
        return fPoints;
    }

next()

SkPoint FwDCubicEvaluator::next ( )

inline

Call next to obtain the SkPoint sampled and move to the next one.

Definition at line 126 of file SkPatchUtils.cpp.

                   {
        SkPoint point = fFwDiff[0];
        fFwDiff[0]    += fFwDiff[1];
        fFwDiff[1]    += fFwDiff[2];
        fFwDiff[2]    += fFwDiff[3];
        fCurrent++;
        return point;
    }

restart()

void FwDCubicEvaluator::restart ( int  divisions )

inline

Restarts the forward differences evaluator to the first value of t = 0.

Definition at line 102 of file SkPatchUtils.cpp.

                                 {
        fDivisions = divisions;
        fCurrent    = 0;
        fMax        = fDivisions + 1;
        skvx::float2 h = 1.f / fDivisions;
        skvx::float2 h2 = h * h;
        skvx::float2 h3 = h2 * h;
        skvx::float2 fwDiff3 = 6 * fCoefs.fA * h3;
        fFwDiff[3] = to_point(fwDiff3);
        fFwDiff[2] = to_point(fwDiff3 + times_2(fCoefs.fB) * h2);
        fFwDiff[1] = to_point(fCoefs.fA * h3 + fCoefs.fB * h2 + fCoefs.fC * h);
        fFwDiff[0] = to_point(fCoefs.fD);
    }

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

• third_party/skia/src/utils/SkPatchUtils.cpp