submodule/skia/src/utils/SkPatchUtils.cpp

   1 /*
   2  * Copyright 2014 Google Inc.
   3  *
   4  * Use of this source code is governed by a BSD-style license that can be
   5  * found in the LICENSE file.
   6  */
   7
   8 #include "src/utils/SkPatchUtils.h"
   9
  10 #include "include/core/SkAlphaType.h"
  11 #include "include/core/SkColorSpace.h"
  12 #include "include/core/SkColorType.h"
  13 #include "include/core/SkImageInfo.h"
  14 #include "include/core/SkMatrix.h"
  15 #include "include/core/SkPoint.h"
  16 #include "include/core/SkScalar.h"
  17 #include "include/core/SkSize.h"
  18 #include "include/core/SkTypes.h"
  19 #include "include/core/SkVertices.h"
  20 #include "include/private/SkColorData.h"
  21 #include "include/private/SkFloatingPoint.h"
  22 #include "include/private/SkTPin.h"
  23 #include "include/private/SkTo.h"
  24 #include "include/private/SkVx.h"
  25 #include "src/core/SkArenaAlloc.h"
  26 #include "src/core/SkColorSpacePriv.h"
  27 #include "src/core/SkConvertPixels.h"
  28 #include "src/core/SkGeometry.h"
  29
  30 #include <string.h>
  31 #include <algorithm>
  32
  33 namespace {
  34     enum CubicCtrlPts {
  35         kTopP0_CubicCtrlPts = 0,
  36         kTopP1_CubicCtrlPts = 1,
  37         kTopP2_CubicCtrlPts = 2,
  38         kTopP3_CubicCtrlPts = 3,
  39
  40         kRightP0_CubicCtrlPts = 3,
  41         kRightP1_CubicCtrlPts = 4,
  42         kRightP2_CubicCtrlPts = 5,
  43         kRightP3_CubicCtrlPts = 6,
  44
  45         kBottomP0_CubicCtrlPts = 9,
  46         kBottomP1_CubicCtrlPts = 8,
  47         kBottomP2_CubicCtrlPts = 7,
  48         kBottomP3_CubicCtrlPts = 6,
  49
  50         kLeftP0_CubicCtrlPts = 0,
  51         kLeftP1_CubicCtrlPts = 11,
  52         kLeftP2_CubicCtrlPts = 10,
  53         kLeftP3_CubicCtrlPts = 9,
  54     };
  55
  56     // Enum for corner also clockwise.
  57     enum Corner {
  58         kTopLeft_Corner = 0,
  59         kTopRight_Corner,
  60         kBottomRight_Corner,
  61         kBottomLeft_Corner
  62     };
  63 }  // namespace
  64
  65 /**
  66  * Evaluator to sample the values of a cubic bezier using forward differences.
  67  * Forward differences is a method for evaluating a nth degree polynomial at a uniform step by only
  68  * adding precalculated values.
  69  * For a linear example we have the function f(t) = m*t+b, then the value of that function at t+h
  70  * would be f(t+h) = m*(t+h)+b. If we want to know the uniform step that we must add to the first
  71  * evaluation f(t) then we need to substract f(t+h) - f(t) = m*t + m*h + b - m*t + b = mh. After
  72  * obtaining this value (mh) we could just add this constant step to our first sampled point
  73  * to compute the next one.
  74  *
  75  * For the cubic case the first difference gives as a result a quadratic polynomial to which we can
  76  * apply again forward differences and get linear function to which we can apply again forward
  77  * differences to get a constant difference. This is why we keep an array of size 4, the 0th
  78  * position keeps the sampled value while the next ones keep the quadratic, linear and constant
  79  * difference values.
  80  */
  81
  82 class FwDCubicEvaluator {
  83
  84 public:
  85
  86     /**
  87      * Receives the 4 control points of the cubic bezier.
  88      */
  89
  90     explicit FwDCubicEvaluator(const SkPoint points[4])
  91             : fCoefs(points) {
  92         memcpy(fPoints, points, 4 * sizeof(SkPoint));
  93
  94         this->restart(1);
  95     }
  96
  97     /**
  98      * Restarts the forward differences evaluator to the first value of t = 0.
  99      */
 100     void restart(int divisions)  {
 101         fDivisions = divisions;
 102         fCurrent    = 0;
 103         fMax        = fDivisions + 1;
 104         skvx::float2 h = 1.f / fDivisions;
 105         skvx::float2 h2 = h * h;
 106         skvx::float2 h3 = h2 * h;
 107         skvx::float2 fwDiff3 = 6 * fCoefs.fA * h3;
 108         fFwDiff[3] = to_point(fwDiff3);
 109         fFwDiff[2] = to_point(fwDiff3 + times_2(fCoefs.fB) * h2);
 110         fFwDiff[1] = to_point(fCoefs.fA * h3 + fCoefs.fB * h2 + fCoefs.fC * h);
 111         fFwDiff[0] = to_point(fCoefs.fD);
 112     }
 113
 114     /**
 115      * Check if the evaluator is still within the range of 0<=t<=1
 116      */
 117     bool done() const {
 118         return fCurrent > fMax;
 119     }
 120
 121     /**
 122      * Call next to obtain the SkPoint sampled and move to the next one.
 123      */
 124     SkPoint next() {
 125         SkPoint point = fFwDiff[0];
 126         fFwDiff[0]    += fFwDiff[1];
 127         fFwDiff[1]    += fFwDiff[2];
 128         fFwDiff[2]    += fFwDiff[3];
 129         fCurrent++;
 130         return point;
 131     }
 132
 133     const SkPoint* getCtrlPoints() const {
 134         return fPoints;
 135     }
 136
 137 private:
 138     SkCubicCoeff fCoefs;
 139     int fMax, fCurrent, fDivisions;
 140     SkPoint fFwDiff[4], fPoints[4];
 141 };
 142
 143 ////////////////////////////////////////////////////////////////////////////////
 144
 145 // size in pixels of each partition per axis, adjust this knob
 146 static const int kPartitionSize = 10;
 147
 148 /**
 149  *  Calculate the approximate arc length given a bezier curve's control points.
 150  *  Returns -1 if bad calc (i.e. non-finite)
 151  */
 152 static SkScalar approx_arc_length(const SkPoint points[], int count) {
 153     if (count < 2) {
 154         return 0;
 155     }
 156     SkScalar arcLength = 0;
 157     for (int i = 0; i < count - 1; i++) {
 158         arcLength += SkPoint::Distance(points[i], points[i + 1]);
 159     }
 160     return SkScalarIsFinite(arcLength) ? arcLength : -1;
 161 }
 162
 163 static SkScalar bilerp(SkScalar tx, SkScalar ty, SkScalar c00, SkScalar c10, SkScalar c01,
 164                        SkScalar c11) {
 165     SkScalar a = c00 * (1.f - tx) + c10 * tx;
 166     SkScalar b = c01 * (1.f - tx) + c11 * tx;
 167     return a * (1.f - ty) + b * ty;
 168 }
 169
 170 static skvx::float4 bilerp(SkScalar tx, SkScalar ty,
 171                            const skvx::float4& c00,
 172                            const skvx::float4& c10,
 173                            const skvx::float4& c01,
 174                            const skvx::float4& c11) {
 175     auto a = c00 * (1.f - tx) + c10 * tx;
 176     auto b = c01 * (1.f - tx) + c11 * tx;
 177     return a * (1.f - ty) + b * ty;
 178 }
 179
 180 SkISize SkPatchUtils::GetLevelOfDetail(const SkPoint cubics[12], const SkMatrix* matrix) {
 181     // Approximate length of each cubic.
 182     SkPoint pts[kNumPtsCubic];
 183     SkPatchUtils::GetTopCubic(cubics, pts);
 184     matrix->mapPoints(pts, kNumPtsCubic);
 185     SkScalar topLength = approx_arc_length(pts, kNumPtsCubic);
 186
 187     SkPatchUtils::GetBottomCubic(cubics, pts);
 188     matrix->mapPoints(pts, kNumPtsCubic);
 189     SkScalar bottomLength = approx_arc_length(pts, kNumPtsCubic);
 190
 191     SkPatchUtils::GetLeftCubic(cubics, pts);
 192     matrix->mapPoints(pts, kNumPtsCubic);
 193     SkScalar leftLength = approx_arc_length(pts, kNumPtsCubic);
 194
 195     SkPatchUtils::GetRightCubic(cubics, pts);
 196     matrix->mapPoints(pts, kNumPtsCubic);
 197     SkScalar rightLength = approx_arc_length(pts, kNumPtsCubic);
 198
 199     if (topLength < 0 || bottomLength < 0 || leftLength < 0 || rightLength < 0) {
 200         return {0, 0};  // negative length is a sentinel for bad length (i.e. non-finite)
 201     }
 202
 203     // Level of detail per axis, based on the larger side between top and bottom or left and right
 204     int lodX = static_cast<int>(std::max(topLength, bottomLength) / kPartitionSize);
 205     int lodY = static_cast<int>(std::max(leftLength, rightLength) / kPartitionSize);
 206
 207     return SkISize::Make(std::max(8, lodX), std::max(8, lodY));
 208 }
 209
 210 void SkPatchUtils::GetTopCubic(const SkPoint cubics[12], SkPoint points[4]) {
 211     points[0] = cubics[kTopP0_CubicCtrlPts];
 212     points[1] = cubics[kTopP1_CubicCtrlPts];
 213     points[2] = cubics[kTopP2_CubicCtrlPts];
 214     points[3] = cubics[kTopP3_CubicCtrlPts];
 215 }
 216
 217 void SkPatchUtils::GetBottomCubic(const SkPoint cubics[12], SkPoint points[4]) {
 218     points[0] = cubics[kBottomP0_CubicCtrlPts];
 219     points[1] = cubics[kBottomP1_CubicCtrlPts];
 220     points[2] = cubics[kBottomP2_CubicCtrlPts];
 221     points[3] = cubics[kBottomP3_CubicCtrlPts];
 222 }
 223
 224 void SkPatchUtils::GetLeftCubic(const SkPoint cubics[12], SkPoint points[4]) {
 225     points[0] = cubics[kLeftP0_CubicCtrlPts];
 226     points[1] = cubics[kLeftP1_CubicCtrlPts];
 227     points[2] = cubics[kLeftP2_CubicCtrlPts];
 228     points[3] = cubics[kLeftP3_CubicCtrlPts];
 229 }
 230
 231 void SkPatchUtils::GetRightCubic(const SkPoint cubics[12], SkPoint points[4]) {
 232     points[0] = cubics[kRightP0_CubicCtrlPts];
 233     points[1] = cubics[kRightP1_CubicCtrlPts];
 234     points[2] = cubics[kRightP2_CubicCtrlPts];
 235     points[3] = cubics[kRightP3_CubicCtrlPts];
 236 }
 237
 238 static void skcolor_to_float(SkPMColor4f* dst, const SkColor* src, int count, SkColorSpace* dstCS) {
 239     SkImageInfo srcInfo = SkImageInfo::Make(count, 1, kBGRA_8888_SkColorType,
 240                                             kUnpremul_SkAlphaType, SkColorSpace::MakeSRGB());
 241     SkImageInfo dstInfo = SkImageInfo::Make(count, 1, kRGBA_F32_SkColorType,
 242                                             kPremul_SkAlphaType, sk_ref_sp(dstCS));
 243     SkAssertResult(SkConvertPixels(dstInfo, dst, 0, srcInfo, src, 0));
 244 }
 245
 246 static void float_to_skcolor(SkColor* dst, const SkPMColor4f* src, int count, SkColorSpace* srcCS) {
 247     SkImageInfo srcInfo = SkImageInfo::Make(count, 1, kRGBA_F32_SkColorType,
 248                                             kPremul_SkAlphaType, sk_ref_sp(srcCS));
 249     SkImageInfo dstInfo = SkImageInfo::Make(count, 1, kBGRA_8888_SkColorType,
 250                                             kUnpremul_SkAlphaType, SkColorSpace::MakeSRGB());
 251     SkAssertResult(SkConvertPixels(dstInfo, dst, 0, srcInfo, src, 0));
 252 }
 253
 254 sk_sp<SkVertices> SkPatchUtils::MakeVertices(const SkPoint cubics[12], const SkColor srcColors[4],
 255                                              const SkPoint srcTexCoords[4], int lodX, int lodY,
 256                                              SkColorSpace* colorSpace) {
 257     if (lodX < 1 || lodY < 1 || nullptr == cubics) {
 258         return nullptr;
 259     }
 260
 261     // check for overflow in multiplication
 262     const int64_t lodX64 = (lodX + 1),
 263     lodY64 = (lodY + 1),
 264     mult64 = lodX64 * lodY64;
 265     if (mult64 > SK_MaxS32) {
 266         return nullptr;
 267     }
 268
 269     // Treat null interpolation space as sRGB.
 270     if (!colorSpace) {
 271         colorSpace = sk_srgb_singleton();
 272     }
 273
 274     int vertexCount = SkToS32(mult64);
 275     // it is recommended to generate draw calls of no more than 65536 indices, so we never generate
 276     // more than 60000 indices. To accomplish that we resize the LOD and vertex count
 277     if (vertexCount > 10000 || lodX > 200 || lodY > 200) {
 278         float weightX = static_cast<float>(lodX) / (lodX + lodY);
 279         float weightY = static_cast<float>(lodY) / (lodX + lodY);
 280
 281         // 200 comes from the 100 * 2 which is the max value of vertices because of the limit of
 282         // 60000 indices ( sqrt(60000 / 6) that comes from data->fIndexCount = lodX * lodY * 6)
 283         // Need a min of 1 since we later divide by lod
 284         lodX = std::max(1, sk_float_floor2int_no_saturate(weightX * 200));
 285         lodY = std::max(1, sk_float_floor2int_no_saturate(weightY * 200));
 286         vertexCount = (lodX + 1) * (lodY + 1);
 287     }
 288     const int indexCount = lodX * lodY * 6;
 289     uint32_t flags = 0;
 290     if (srcTexCoords) {
 291         flags |= SkVertices::kHasTexCoords_BuilderFlag;
 292     }
 293     if (srcColors) {
 294         flags |= SkVertices::kHasColors_BuilderFlag;
 295     }
 296
 297     SkSTArenaAlloc<2048> alloc;
 298     SkPMColor4f* cornerColors = srcColors ? alloc.makeArray<SkPMColor4f>(4) : nullptr;
 299     SkPMColor4f* tmpColors = srcColors ? alloc.makeArray<SkPMColor4f>(vertexCount) : nullptr;
 300
 301     SkVertices::Builder builder(SkVertices::kTriangles_VertexMode, vertexCount, indexCount, flags);
 302     SkPoint* pos = builder.positions();
 303     SkPoint* texs = builder.texCoords();
 304     uint16_t* indices = builder.indices();
 305
 306     if (cornerColors) {
 307         skcolor_to_float(cornerColors, srcColors, kNumCorners, colorSpace);
 308     }
 309
 310     SkPoint pts[kNumPtsCubic];
 311     SkPatchUtils::GetBottomCubic(cubics, pts);
 312     FwDCubicEvaluator fBottom(pts);
 313     SkPatchUtils::GetTopCubic(cubics, pts);
 314     FwDCubicEvaluator fTop(pts);
 315     SkPatchUtils::GetLeftCubic(cubics, pts);
 316     FwDCubicEvaluator fLeft(pts);
 317     SkPatchUtils::GetRightCubic(cubics, pts);
 318     FwDCubicEvaluator fRight(pts);
 319
 320     fBottom.restart(lodX);
 321     fTop.restart(lodX);
 322
 323     SkScalar u = 0.0f;
 324     int stride = lodY + 1;
 325     for (int x = 0; x <= lodX; x++) {
 326         SkPoint bottom = fBottom.next(), top = fTop.next();
 327         fLeft.restart(lodY);
 328         fRight.restart(lodY);
 329         SkScalar v = 0.f;
 330         for (int y = 0; y <= lodY; y++) {
 331             int dataIndex = x * (lodY + 1) + y;
 332
 333             SkPoint left = fLeft.next(), right = fRight.next();
 334
 335             SkPoint s0 = SkPoint::Make((1.0f - v) * top.x() + v * bottom.x(),
 336                                        (1.0f - v) * top.y() + v * bottom.y());
 337             SkPoint s1 = SkPoint::Make((1.0f - u) * left.x() + u * right.x(),
 338                                        (1.0f - u) * left.y() + u * right.y());
 339             SkPoint s2 = SkPoint::Make(
 340                                        (1.0f - v) * ((1.0f - u) * fTop.getCtrlPoints()[0].x()
 341                                                      + u * fTop.getCtrlPoints()[3].x())
 342                                        + v * ((1.0f - u) * fBottom.getCtrlPoints()[0].x()
 343                                               + u * fBottom.getCtrlPoints()[3].x()),
 344                                        (1.0f - v) * ((1.0f - u) * fTop.getCtrlPoints()[0].y()
 345                                                      + u * fTop.getCtrlPoints()[3].y())
 346                                        + v * ((1.0f - u) * fBottom.getCtrlPoints()[0].y()
 347                                               + u * fBottom.getCtrlPoints()[3].y()));
 348             pos[dataIndex] = s0 + s1 - s2;
 349
 350             if (cornerColors) {
 351                 bilerp(u, v, skvx::float4::Load(cornerColors[kTopLeft_Corner].vec()),
 352                              skvx::float4::Load(cornerColors[kTopRight_Corner].vec()),
 353                              skvx::float4::Load(cornerColors[kBottomLeft_Corner].vec()),
 354                              skvx::float4::Load(cornerColors[kBottomRight_Corner].vec()))
 355                     .store(tmpColors[dataIndex].vec());
 356             }
 357
 358             if (texs) {
 359                 texs[dataIndex] = SkPoint::Make(bilerp(u, v, srcTexCoords[kTopLeft_Corner].x(),
 360                                                        srcTexCoords[kTopRight_Corner].x(),
 361                                                        srcTexCoords[kBottomLeft_Corner].x(),
 362                                                        srcTexCoords[kBottomRight_Corner].x()),
 363                                                 bilerp(u, v, srcTexCoords[kTopLeft_Corner].y(),
 364                                                        srcTexCoords[kTopRight_Corner].y(),
 365                                                        srcTexCoords[kBottomLeft_Corner].y(),
 366                                                        srcTexCoords[kBottomRight_Corner].y()));
 367
 368             }
 369
 370             if(x < lodX && y < lodY) {
 371                 int i = 6 * (x * lodY + y);
 372                 indices[i] = x * stride + y;
 373                 indices[i + 1] = x * stride + 1 + y;
 374                 indices[i + 2] = (x + 1) * stride + 1 + y;
 375                 indices[i + 3] = indices[i];
 376                 indices[i + 4] = indices[i + 2];
 377                 indices[i + 5] = (x + 1) * stride + y;
 378             }
 379             v = SkTPin(v + 1.f / lodY, 0.0f, 1.0f);
 380         }
 381         u = SkTPin(u + 1.f / lodX, 0.0f, 1.0f);
 382     }
 383
 384     if (tmpColors) {
 385         float_to_skcolor(builder.colors(), tmpColors, vertexCount, colorSpace);
 386     }
 387     return builder.detach();
 388 }