gfx/skia/trunk/src/core/SkPatch.cpp
 author George Wright Mon, 28 Jul 2014 15:06:12 -0400 changeset 220765 883cd6be06d294600562435ebea87d2804bca957 permissions -rw-r--r--
[PATCH 08/15] Bug 1017113 - Update Skia to 2014-07-28 r=upstream
```
/*
*
* Use of this source code is governed by a BSD-style license that can be
* found in the LICENSE file.
*/

#include "SkPatch.h"

#include "SkGeometry.h"
#include "SkColorPriv.h"

////////////////////////////////////////////////////////////////////////////////

/**
* 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
* 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.
*/

class FwDCubicEvaluator {

public:
FwDCubicEvaluator() { }

/**
* Receives the 4 control points of the cubic bezier.
*/
FwDCubicEvaluator(SkPoint a, SkPoint b, SkPoint c, SkPoint d) {
fPoints[0] = a;
fPoints[1] = b;
fPoints[2] = c;
fPoints[3] = d;

SkScalar cx[4], cy[4];
SkGetCubicCoeff(fPoints, cx, cy);
fCoefs[0].set(cx[0], cy[0]);
fCoefs[1].set(cx[1], cy[1]);
fCoefs[2].set(cx[2], cy[2]);
fCoefs[3].set(cx[3], cy[3]);

this->restart(1);
}

/**
* Restarts the forward differences evaluator to the first value of t = 0.
*/
void restart(int divisions) {
fDivisions = divisions;
SkScalar h  = 1.f / fDivisions;
fCurrent    = 0;
fMax        = fDivisions + 1;
fFwDiff[0]  = fCoefs[3];
SkScalar h2 = h * h;
SkScalar h3 = h2 * h;

fFwDiff[3].set(6.f * fCoefs[0].x() * h3, 6.f * fCoefs[0].y() * h3); //6ah^3
fFwDiff[2].set(fFwDiff[3].x() + 2.f * fCoefs[1].x() * h2, //6ah^3 + 2bh^2
fFwDiff[3].y() + 2.f * fCoefs[1].y() * h2);
fFwDiff[1].set(fCoefs[0].x() * h3 + fCoefs[1].x() * h2 + fCoefs[2].x() * h,//ah^3 + bh^2 +ch
fCoefs[0].y() * h3 + fCoefs[1].y() * h2 + fCoefs[2].y() * h);
}

/**
* Check if the evaluator is still within the range of 0<=t<=1
*/
bool done() const {
return fCurrent > fMax;
}

/**
* Call next to obtain the SkPoint sampled and move to the next one.
*/
SkPoint next() {
SkPoint point = fFwDiff[0];
fFwDiff[0]    += fFwDiff[1];
fFwDiff[1]    += fFwDiff[2];
fFwDiff[2]    += fFwDiff[3];
fCurrent++;
return point;
}

const SkPoint* getCtrlPoints() const {
return fPoints;
}

private:
int fMax, fCurrent, fDivisions;
SkPoint fFwDiff[4], fCoefs[4], fPoints[4];
};

////////////////////////////////////////////////////////////////////////////////

SkPatch::SkPatch(SkPoint points[12], SkColor colors[4]) {

for (int i = 0; i<12; i++) {
fCtrlPoints[i] = points[i];
}

fCornerColors[0] = SkPreMultiplyColor(colors[0]);
fCornerColors[1] = SkPreMultiplyColor(colors[1]);
fCornerColors[2] = SkPreMultiplyColor(colors[2]);
fCornerColors[3] = SkPreMultiplyColor(colors[3]);
}

uint8_t bilinear(SkScalar tx, SkScalar ty, SkScalar c00, SkScalar c10, SkScalar c01, SkScalar c11) {
SkScalar a = c00 * (1.f - tx) + c10 * tx;
SkScalar b = c01 * (1.f - tx) + c11 * tx;
return uint8_t(a * (1.f - ty) + b * ty);
}

bool SkPatch::getVertexData(SkPatch::VertexData* data, int divisions) {

if (divisions < 1) {
return false;
}

int divX = divisions, divY = divisions;

data->fVertexCount = (divX + 1) * (divY + 1);
data->fIndexCount = divX * divY * 6;

data->fPoints = SkNEW_ARRAY(SkPoint, data->fVertexCount);
data->fColors = SkNEW_ARRAY(uint32_t, data->fVertexCount);
data->fTexCoords = SkNEW_ARRAY(SkPoint, data->fVertexCount);
data->fIndices = SkNEW_ARRAY(uint16_t, data->fIndexCount);

FwDCubicEvaluator fBottom(fCtrlPoints[kBottomP0_CubicCtrlPts],
fCtrlPoints[kBottomP1_CubicCtrlPts],
fCtrlPoints[kBottomP2_CubicCtrlPts],
fCtrlPoints[kBottomP3_CubicCtrlPts]),
fTop(fCtrlPoints[kTopP0_CubicCtrlPts],
fCtrlPoints[kTopP1_CubicCtrlPts],
fCtrlPoints[kTopP2_CubicCtrlPts],
fCtrlPoints[kTopP2_CubicCtrlPts]),
fLeft(fCtrlPoints[kLeftP0_CubicCtrlPts],
fCtrlPoints[kLeftP1_CubicCtrlPts],
fCtrlPoints[kLeftP2_CubicCtrlPts],
fCtrlPoints[kLeftP3_CubicCtrlPts]),
fRight(fCtrlPoints[kRightP0_CubicCtrlPts],
fCtrlPoints[kRightP1_CubicCtrlPts],
fCtrlPoints[kRightP2_CubicCtrlPts],
fCtrlPoints[kRightP3_CubicCtrlPts]);

fBottom.restart(divX);
fTop.restart(divX);

SkScalar u = 0.0f;
int stride = divY + 1;
for (int x = 0; x <= divX; x++) {
SkPoint bottom = fBottom.next(), top = fTop.next();
fLeft.restart(divY);
fRight.restart(divY);
SkScalar v = 0.f;
for (int y = 0; y <= divY; y++) {
int dataIndex = x * (divX + 1) + y;

SkPoint left = fLeft.next(), right = fRight.next();

SkPoint s0 = SkPoint::Make((1.0f - v) * top.x() + v * bottom.x(),
(1.0f - v) * top.y() + v * bottom.y());
SkPoint s1 = SkPoint::Make((1.0f - u) * left.x() + u * right.x(),
(1.0f - u) * left.y() + u * right.y());
SkPoint s2 = SkPoint::Make(
(1.0f - v) * ((1.0f - u) * fTop.getCtrlPoints()[0].x()
+ u * fTop.getCtrlPoints()[3].x())
+ v * ((1.0f - u) * fBottom.getCtrlPoints()[0].x()
+ u * fBottom.getCtrlPoints()[3].x()),
(1.0f - v) * ((1.0f - u) * fTop.getCtrlPoints()[0].y()
+ u * fTop.getCtrlPoints()[3].y())
+ v * ((1.0f - u) * fBottom.getCtrlPoints()[0].y()
+ u * fBottom.getCtrlPoints()[3].y()));
data->fPoints[dataIndex] = s0 + s1 - s2;

uint8_t a = bilinear(u, v,
SkScalar(SkColorGetA(fCornerColors[0])),
SkScalar(SkColorGetA(fCornerColors[1])),
SkScalar(SkColorGetA(fCornerColors[2])),
SkScalar(SkColorGetA(fCornerColors[3])));
uint8_t r = bilinear(u, v,
SkScalar(SkColorGetR(fCornerColors[0])),
SkScalar(SkColorGetR(fCornerColors[1])),
SkScalar(SkColorGetR(fCornerColors[2])),
SkScalar(SkColorGetR(fCornerColors[3])));
uint8_t g = bilinear(u, v,
SkScalar(SkColorGetG(fCornerColors[0])),
SkScalar(SkColorGetG(fCornerColors[1])),
SkScalar(SkColorGetG(fCornerColors[2])),
SkScalar(SkColorGetG(fCornerColors[3])));
uint8_t b = bilinear(u, v,
SkScalar(SkColorGetB(fCornerColors[0])),
SkScalar(SkColorGetB(fCornerColors[1])),
SkScalar(SkColorGetB(fCornerColors[2])),
SkScalar(SkColorGetB(fCornerColors[3])));
data->fColors[dataIndex] = SkPackARGB32(a,r,g,b);

data->fTexCoords[dataIndex] = SkPoint::Make(u, v);

if(x < divX && y < divY) {
int i = 6 * (x * divY + y);
data->fIndices[i] = x * stride + y;
data->fIndices[i + 1] = x * stride + 1 + y;
data->fIndices[i + 2] = (x + 1) * stride + 1 + y;
data->fIndices[i + 3] = data->fIndices[i];
data->fIndices[i + 4] = data->fIndices[i + 2];
data->fIndices[i + 5] = (x + 1) * stride + y;
}
v += 1.f / divY;
}
u += 1.f / divX;
}
return true;
}
```