| /* |
| * 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" |
| |
| //////////////////////////////////////////////////////////////////////////////// |
| |
| /** |
| * 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); |
| } |
| |
| /** |
| * 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; |
| } |