SkCanvas::drawPatch param SkPoint[12]

src/core/SkPatch.cpp

-/*
- * Copyright 2014 Google Inc.
- *
- * 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"
-#include "SkBuffer.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
- * 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.
- */
-
-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);
-    }
-    
-    explicit FwDCubicEvaluator(SkPoint points[4]) {
-        for (int i = 0; i< 4; i++) {
-            fPoints[i] = points[i];
-        }
-        
-        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(const SkPoint points[12], const SkColor colors[4]) {
-    this->reset(points, colors);
-}
-
-static uint8_t bilerp(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 lodX, int lodY) const {
-    
-    if (lodX < 1 || lodY < 1) {
-        return false;
-    }
-    
-    // premultiply colors to avoid color bleeding. 
-    SkPMColor colors[SkPatch::kNumColors];
-    for (int i = 0; i < SkPatch::kNumColors; i++) {
-        colors[i] = SkPreMultiplyColor(fCornerColors[i]);
-    }
-    
-    // number of indices is limited by size of uint16_t, so we clamp it to avoid overflow
-    data->fVertexCount = SkMin32((lodX + 1) * (lodY + 1), 65536);
-    lodX  = SkMin32(lodX, 255);
-    lodY  = SkMin32(lodY, 255);
-    data->fIndexCount = lodX * lodY * 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);
-    
-    SkPoint pts[SkPatch::kNumPtsCubic];
-    this->getBottomPoints(pts);
-    FwDCubicEvaluator fBottom(pts);
-    this->getTopPoints(pts);
-    FwDCubicEvaluator fTop(pts);
-    this->getLeftPoints(pts);
-    FwDCubicEvaluator fLeft(pts);
-    this->getRightPoints(pts);
-    FwDCubicEvaluator fRight(pts);
-
-    fBottom.restart(lodX);
-    fTop.restart(lodX);
-
-    SkScalar u = 0.0f;
-    int stride = lodY + 1;
-    for (int x = 0; x <= lodX; x++) {
-        SkPoint bottom = fBottom.next(), top = fTop.next();
-        fLeft.restart(lodY);
-        fRight.restart(lodY);
-        SkScalar v = 0.f;
-        for (int y = 0; y <= lodY; y++) {
-            int dataIndex = x * (lodY + 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 = bilerp(u, v,
-                            SkScalar(SkColorGetA(colors[kTopLeft_CornerColors])),
-                            SkScalar(SkColorGetA(colors[kTopRight_CornerColors])),
-                            SkScalar(SkColorGetA(colors[kBottomLeft_CornerColors])),
-                            SkScalar(SkColorGetA(colors[kBottomRight_CornerColors])));
-            uint8_t r = bilerp(u, v,
-                            SkScalar(SkColorGetR(colors[kTopLeft_CornerColors])),
-                            SkScalar(SkColorGetR(colors[kTopRight_CornerColors])),
-                            SkScalar(SkColorGetR(colors[kBottomLeft_CornerColors])),
-                            SkScalar(SkColorGetR(colors[kBottomRight_CornerColors])));
-            uint8_t g = bilerp(u, v,
-                            SkScalar(SkColorGetG(colors[kTopLeft_CornerColors])),
-                            SkScalar(SkColorGetG(colors[kTopRight_CornerColors])),
-                            SkScalar(SkColorGetG(colors[kBottomLeft_CornerColors])),
-                            SkScalar(SkColorGetG(colors[kBottomRight_CornerColors])));
-            uint8_t b = bilerp(u, v, 
-                            SkScalar(SkColorGetB(colors[kTopLeft_CornerColors])),
-                            SkScalar(SkColorGetB(colors[kTopRight_CornerColors])),
-                            SkScalar(SkColorGetB(colors[kBottomLeft_CornerColors])),
-                            SkScalar(SkColorGetB(colors[kBottomRight_CornerColors])));
-            data->fColors[dataIndex] = SkPackARGB32(a,r,g,b);
-            
-            data->fTexCoords[dataIndex] = SkPoint::Make(u, v);
-
-            if(x < lodX && y < lodY) {
-                int i = 6 * (x * lodY + 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 = SkScalarClampMax(v + 1.f / lodY, 1);
-        }
-        u = SkScalarClampMax(u + 1.f / lodX, 1);
-    }
-    return true;
-}
-
-size_t SkPatch::writeToMemory(void* storage) const {
-    int byteCount =  kNumCtrlPts * sizeof(SkPoint) + kNumColors * sizeof(SkColor);
-    
-    if (NULL == storage) {
-        return SkAlign4(byteCount);
-    }
-    
-    SkWBuffer buffer(storage);
-    
-    buffer.write(fCtrlPoints, kNumCtrlPts * sizeof(SkPoint));
-    buffer.write(fCornerColors, kNumColors * sizeof(SkColor));
-    
-    buffer.padToAlign4();
-    return buffer.pos();
-}
-
-size_t SkPatch::readFromMemory(const void* storage, size_t length) {
-    SkRBufferWithSizeCheck buffer(storage, length);
-    
-    if (!buffer.read(fCtrlPoints, kNumCtrlPts * sizeof(SkPoint))) {
-        return 0;
-    }
-    
-    if (!buffer.read(fCornerColors, kNumColors * sizeof(SkColor))) {
-        return 0;
-    }
-    return kNumCtrlPts * sizeof(SkPoint) + kNumColors * sizeof(SkColor);
-}