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/*
* 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 "SkPatchUtils.h"
#include "SkColorData.h"
#include "SkColorSpace_Base.h"
#include "SkGeometry.h"
#include "SkPM4f.h"
namespace {
enum CubicCtrlPts {
kTopP0_CubicCtrlPts = 0,
kTopP1_CubicCtrlPts = 1,
kTopP2_CubicCtrlPts = 2,
kTopP3_CubicCtrlPts = 3,
kRightP0_CubicCtrlPts = 3,
kRightP1_CubicCtrlPts = 4,
kRightP2_CubicCtrlPts = 5,
kRightP3_CubicCtrlPts = 6,
kBottomP0_CubicCtrlPts = 9,
kBottomP1_CubicCtrlPts = 8,
kBottomP2_CubicCtrlPts = 7,
kBottomP3_CubicCtrlPts = 6,
kLeftP0_CubicCtrlPts = 0,
kLeftP1_CubicCtrlPts = 11,
kLeftP2_CubicCtrlPts = 10,
kLeftP3_CubicCtrlPts = 9,
};
// Enum for corner also clockwise.
enum Corner {
kTopLeft_Corner = 0,
kTopRight_Corner,
kBottomRight_Corner,
kBottomLeft_Corner
};
}
/**
* 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:
/**
* Receives the 4 control points of the cubic bezier.
*/
explicit FwDCubicEvaluator(const SkPoint points[4])
: fCoefs(points) {
memcpy(fPoints, points, 4 * sizeof(SkPoint));
this->restart(1);
}
/**
* Restarts the forward differences evaluator to the first value of t = 0.
*/
void restart(int divisions) {
fDivisions = divisions;
fCurrent = 0;
fMax = fDivisions + 1;
Sk2s h = Sk2s(1.f / fDivisions);
Sk2s h2 = h * h;
Sk2s h3 = h2 * h;
Sk2s fwDiff3 = Sk2s(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);
}
/**
* 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:
SkCubicCoeff fCoefs;
int fMax, fCurrent, fDivisions;
SkPoint fFwDiff[4], fPoints[4];
};
////////////////////////////////////////////////////////////////////////////////
// size in pixels of each partition per axis, adjust this knob
static const int kPartitionSize = 10;
/**
* Calculate the approximate arc length given a bezier curve's control points.
*/
static SkScalar approx_arc_length(SkPoint* points, int count) {
if (count < 2) {
return 0;
}
SkScalar arcLength = 0;
for (int i = 0; i < count - 1; i++) {
arcLength += SkPoint::Distance(points[i], points[i + 1]);
}
return arcLength;
}
static SkScalar 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 a * (1.f - ty) + b * ty;
}
static Sk4f bilerp(SkScalar tx, SkScalar ty,
const Sk4f& c00, const Sk4f& c10, const Sk4f& c01, const Sk4f& c11) {
Sk4f a = c00 * (1.f - tx) + c10 * tx;
Sk4f b = c01 * (1.f - tx) + c11 * tx;
return a * (1.f - ty) + b * ty;
}
SkISize SkPatchUtils::GetLevelOfDetail(const SkPoint cubics[12], const SkMatrix* matrix) {
// Approximate length of each cubic.
SkPoint pts[kNumPtsCubic];
SkPatchUtils::GetTopCubic(cubics, pts);
matrix->mapPoints(pts, kNumPtsCubic);
SkScalar topLength = approx_arc_length(pts, kNumPtsCubic);
SkPatchUtils::GetBottomCubic(cubics, pts);
matrix->mapPoints(pts, kNumPtsCubic);
SkScalar bottomLength = approx_arc_length(pts, kNumPtsCubic);
SkPatchUtils::GetLeftCubic(cubics, pts);
matrix->mapPoints(pts, kNumPtsCubic);
SkScalar leftLength = approx_arc_length(pts, kNumPtsCubic);
SkPatchUtils::GetRightCubic(cubics, pts);
matrix->mapPoints(pts, kNumPtsCubic);
SkScalar rightLength = approx_arc_length(pts, kNumPtsCubic);
// Level of detail per axis, based on the larger side between top and bottom or left and right
int lodX = static_cast<int>(SkMaxScalar(topLength, bottomLength) / kPartitionSize);
int lodY = static_cast<int>(SkMaxScalar(leftLength, rightLength) / kPartitionSize);
return SkISize::Make(SkMax32(8, lodX), SkMax32(8, lodY));
}
void SkPatchUtils::GetTopCubic(const SkPoint cubics[12], SkPoint points[4]) {
points[0] = cubics[kTopP0_CubicCtrlPts];
points[1] = cubics[kTopP1_CubicCtrlPts];
points[2] = cubics[kTopP2_CubicCtrlPts];
points[3] = cubics[kTopP3_CubicCtrlPts];
}
void SkPatchUtils::GetBottomCubic(const SkPoint cubics[12], SkPoint points[4]) {
points[0] = cubics[kBottomP0_CubicCtrlPts];
points[1] = cubics[kBottomP1_CubicCtrlPts];
points[2] = cubics[kBottomP2_CubicCtrlPts];
points[3] = cubics[kBottomP3_CubicCtrlPts];
}
void SkPatchUtils::GetLeftCubic(const SkPoint cubics[12], SkPoint points[4]) {
points[0] = cubics[kLeftP0_CubicCtrlPts];
points[1] = cubics[kLeftP1_CubicCtrlPts];
points[2] = cubics[kLeftP2_CubicCtrlPts];
points[3] = cubics[kLeftP3_CubicCtrlPts];
}
void SkPatchUtils::GetRightCubic(const SkPoint cubics[12], SkPoint points[4]) {
points[0] = cubics[kRightP0_CubicCtrlPts];
points[1] = cubics[kRightP1_CubicCtrlPts];
points[2] = cubics[kRightP2_CubicCtrlPts];
points[3] = cubics[kRightP3_CubicCtrlPts];
}
#include "SkPM4fPriv.h"
#include "SkColorSpace_Base.h"
#include "SkColorSpaceXform.h"
struct SkRGBAf {
float fVec[4];
static SkRGBAf From4f(const Sk4f& x) {
SkRGBAf c;
x.store(c.fVec);
return c;
}
static SkRGBAf FromBGRA32(SkColor c) {
return From4f(swizzle_rb(SkNx_cast<float>(Sk4b::Load(&c)) * (1/255.0f)));
}
Sk4f to4f() const {
return Sk4f::Load(fVec);
}
SkColor toBGRA32() const {
SkColor color;
SkNx_cast<uint8_t>(swizzle_rb(this->to4f()) * Sk4f(255) + Sk4f(0.5f)).store(&color);
return color;
}
SkRGBAf premul() const {
float a = fVec[3];
return From4f(this->to4f() * Sk4f(a, a, a, 1));
}
SkRGBAf unpremul() const {
float a = fVec[3];
float inv = a ? 1/a : 0;
return From4f(this->to4f() * Sk4f(inv, inv, inv, 1));
}
};
static void skcolor_to_linear(SkRGBAf dst[], const SkColor src[], int count, SkColorSpace* cs,
bool doPremul) {
if (cs) {
auto srcCS = SkColorSpace::MakeSRGB();
auto dstCS = as_CSB(cs)->makeLinearGamma();
auto op = doPremul ? SkColorSpaceXform::kPremul_AlphaOp
: SkColorSpaceXform::kPreserve_AlphaOp;
SkColorSpaceXform::Apply(dstCS.get(), SkColorSpaceXform::kRGBA_F32_ColorFormat, dst,
srcCS.get(), SkColorSpaceXform::kBGRA_8888_ColorFormat, src,
count, op);
} else {
for (int i = 0; i < count; ++i) {
dst[i] = SkRGBAf::FromBGRA32(src[i]);
if (doPremul) {
dst[i] = dst[i].premul();
}
}
}
}
static void linear_to_skcolor(SkColor dst[], const SkRGBAf src[], int count, SkColorSpace* cs) {
if (cs) {
auto srcCS = as_CSB(cs)->makeLinearGamma();
auto dstCS = SkColorSpace::MakeSRGB();
SkColorSpaceXform::Apply(dstCS.get(), SkColorSpaceXform::kBGRA_8888_ColorFormat, dst,
srcCS.get(), SkColorSpaceXform::kRGBA_F32_ColorFormat, src,
count, SkColorSpaceXform::kPreserve_AlphaOp);
} else {
for (int i = 0; i < count; ++i) {
dst[i] = src[i].toBGRA32();
}
}
}
static void unpremul(SkRGBAf array[], int count) {
for (int i = 0; i < count; ++i) {
array[i] = array[i].unpremul();
}
}
sk_sp<SkVertices> SkPatchUtils::MakeVertices(const SkPoint cubics[12], const SkColor srcColors[4],
const SkPoint srcTexCoords[4], int lodX, int lodY,
bool interpColorsLinearly) {
if (lodX < 1 || lodY < 1 || nullptr == cubics) {
return nullptr;
}
// check for overflow in multiplication
const int64_t lodX64 = (lodX + 1),
lodY64 = (lodY + 1),
mult64 = lodX64 * lodY64;
if (mult64 > SK_MaxS32) {
return nullptr;
}
int vertexCount = SkToS32(mult64);
// it is recommended to generate draw calls of no more than 65536 indices, so we never generate
// more than 60000 indices. To accomplish that we resize the LOD and vertex count
if (vertexCount > 10000 || lodX > 200 || lodY > 200) {
float weightX = static_cast<float>(lodX) / (lodX + lodY);
float weightY = static_cast<float>(lodY) / (lodX + lodY);
// 200 comes from the 100 * 2 which is the max value of vertices because of the limit of
// 60000 indices ( sqrt(60000 / 6) that comes from data->fIndexCount = lodX * lodY * 6)
lodX = static_cast<int>(weightX * 200);
lodY = static_cast<int>(weightY * 200);
vertexCount = (lodX + 1) * (lodY + 1);
}
const int indexCount = lodX * lodY * 6;
uint32_t flags = 0;
if (srcTexCoords) {
flags |= SkVertices::kHasTexCoords_BuilderFlag;
}
if (srcColors) {
flags |= SkVertices::kHasColors_BuilderFlag;
}
SkSTArenaAlloc<2048> alloc;
SkRGBAf* cornerColors = srcColors ? alloc.makeArray<SkRGBAf>(4) : nullptr;
SkRGBAf* tmpColors = srcColors ? alloc.makeArray<SkRGBAf>(vertexCount) : nullptr;
auto convertCS = interpColorsLinearly ? SkColorSpace::MakeSRGB() : nullptr;
SkVertices::Builder builder(SkVertices::kTriangles_VertexMode, vertexCount, indexCount, flags);
SkPoint* pos = builder.positions();
SkPoint* texs = builder.texCoords();
uint16_t* indices = builder.indices();
bool is_opaque = false;
/*
* 1. Should we offer this as a runtime choice, as we do in gradients?
* 2. Since drawing the vertices wants premul, shoudl we extend SkVertices to store
* premul colors (as floats, w/ a colorspace)?
*/
bool doPremul = true;
if (cornerColors) {
SkColor c = ~0;
for (int i = 0; i < kNumCorners; i++) {
c &= srcColors[i];
}
is_opaque = (SkColorGetA(c) == 0xFF);
if (is_opaque) {
doPremul = false; // no need
}
skcolor_to_linear(cornerColors, srcColors, kNumCorners, convertCS.get(), doPremul);
}
SkPoint pts[kNumPtsCubic];
SkPatchUtils::GetBottomCubic(cubics, pts);
FwDCubicEvaluator fBottom(pts);
SkPatchUtils::GetTopCubic(cubics, pts);
FwDCubicEvaluator fTop(pts);
SkPatchUtils::GetLeftCubic(cubics, pts);
FwDCubicEvaluator fLeft(pts);
SkPatchUtils::GetRightCubic(cubics, 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()));
pos[dataIndex] = s0 + s1 - s2;
if (cornerColors) {
bilerp(u, v, cornerColors[kTopLeft_Corner].to4f(),
cornerColors[kTopRight_Corner].to4f(),
cornerColors[kBottomLeft_Corner].to4f(),
cornerColors[kBottomRight_Corner].to4f()).store(tmpColors[dataIndex].fVec);
if (is_opaque) {
tmpColors[dataIndex].fVec[3] = 1;
}
}
if (texs) {
texs[dataIndex] = SkPoint::Make(bilerp(u, v, srcTexCoords[kTopLeft_Corner].x(),
srcTexCoords[kTopRight_Corner].x(),
srcTexCoords[kBottomLeft_Corner].x(),
srcTexCoords[kBottomRight_Corner].x()),
bilerp(u, v, srcTexCoords[kTopLeft_Corner].y(),
srcTexCoords[kTopRight_Corner].y(),
srcTexCoords[kBottomLeft_Corner].y(),
srcTexCoords[kBottomRight_Corner].y()));
}
if(x < lodX && y < lodY) {
int i = 6 * (x * lodY + y);
indices[i] = x * stride + y;
indices[i + 1] = x * stride + 1 + y;
indices[i + 2] = (x + 1) * stride + 1 + y;
indices[i + 3] = indices[i];
indices[i + 4] = indices[i + 2];
indices[i + 5] = (x + 1) * stride + y;
}
v = SkScalarClampMax(v + 1.f / lodY, 1);
}
u = SkScalarClampMax(u + 1.f / lodX, 1);
}
if (tmpColors) {
if (doPremul) {
unpremul(tmpColors, vertexCount);
}
linear_to_skcolor(builder.colors(), tmpColors, vertexCount, convertCS.get());
}
return builder.detach();
}