SkSweepGradient.cpp revision 868a8e7fc83e9ac6ee1418e75b84a0595605626c 
1
2/*
3 * Copyright 2012 Google Inc.
4 *
5 * Use of this source code is governed by a BSD-style license that can be
6 * found in the LICENSE file.
7 */
8
9#include "SkSweepGradient.h"
10
11SkSweepGradient::SkSweepGradient(SkScalar cx, SkScalar cy, const SkColor colors[],
12               const SkScalar pos[], int count, SkUnitMapper* mapper)
13: SkGradientShaderBase(colors, pos, count, SkShader::kClamp_TileMode, mapper),
14  fCenter(SkPoint::Make(cx, cy))
15{
16    fPtsToUnit.setTranslate(-cx, -cy);
17}
18
19SkShader::BitmapType SkSweepGradient::asABitmap(SkBitmap* bitmap,
20    SkMatrix* matrix, SkShader::TileMode* xy) const {
21    if (bitmap) {
22        this->getGradientTableBitmap(bitmap);
23    }
24    if (matrix) {
25        *matrix = fPtsToUnit;
26    }
27    if (xy) {
28        xy[0] = fTileMode;
29        xy[1] = kClamp_TileMode;
30    }
31    return kSweep_BitmapType;
32}
33
34SkShader::GradientType SkSweepGradient::asAGradient(GradientInfo* info) const {
35    if (info) {
36        commonAsAGradient(info);
37        info->fPoint[0] = fCenter;
38    }
39    return kSweep_GradientType;
40}
41
42SkSweepGradient::SkSweepGradient(SkFlattenableReadBuffer& buffer)
43    : INHERITED(buffer),
44      fCenter(buffer.readPoint()) {
45}
46
47void SkSweepGradient::flatten(SkFlattenableWriteBuffer& buffer) const {
48    this->INHERITED::flatten(buffer);
49    buffer.writePoint(fCenter);
50}
51
52#ifndef SK_SCALAR_IS_FLOAT
53#ifdef COMPUTE_SWEEP_TABLE
54#define PI  3.14159265
55static bool gSweepTableReady;
56static uint8_t gSweepTable[65];
57
58/*  Our table stores precomputed values for atan: [0...1] -> [0..PI/4]
59    We scale the results to [0..32]
60*/
61static const uint8_t* build_sweep_table() {
62    if (!gSweepTableReady) {
63        const int N = 65;
64        const double DENOM = N - 1;
65
66        for (int i = 0; i < N; i++)
67        {
68            double arg = i / DENOM;
69            double v = atan(arg);
70            int iv = (int)round(v * DENOM * 2 / PI);
71//            printf("[%d] atan(%g) = %g %d\n", i, arg, v, iv);
72            printf("%d, ", iv);
73            gSweepTable[i] = iv;
74        }
75        gSweepTableReady = true;
76    }
77    return gSweepTable;
78}
79#else
80static const uint8_t gSweepTable[] = {
81    0, 1, 1, 2, 3, 3, 4, 4, 5, 6, 6, 7, 8, 8, 9, 9,
82    10, 11, 11, 12, 12, 13, 13, 14, 15, 15, 16, 16, 17, 17, 18, 18,
83    19, 19, 20, 20, 21, 21, 22, 22, 23, 23, 24, 24, 25, 25, 25, 26,
84    26, 27, 27, 27, 28, 28, 29, 29, 29, 30, 30, 30, 31, 31, 31, 32,
85    32
86};
87static const uint8_t* build_sweep_table() { return gSweepTable; }
88#endif
89#endif
90
91// divide numer/denom, with a bias of 6bits. Assumes numer <= denom
92// and denom != 0. Since our table is 6bits big (+1), this is a nice fit.
93// Same as (but faster than) SkFixedDiv(numer, denom) >> 10
94
95//unsigned div_64(int numer, int denom);
96#ifndef SK_SCALAR_IS_FLOAT
97static unsigned div_64(int numer, int denom) {
98    SkASSERT(numer <= denom);
99    SkASSERT(numer > 0);
100    SkASSERT(denom > 0);
101
102    int nbits = SkCLZ(numer);
103    int dbits = SkCLZ(denom);
104    int bits = 6 - nbits + dbits;
105    SkASSERT(bits <= 6);
106
107    if (bits < 0) {  // detect underflow
108        return 0;
109    }
110
111    denom <<= dbits - 1;
112    numer <<= nbits - 1;
113
114    unsigned result = 0;
115
116    // do the first one
117    if ((numer -= denom) >= 0) {
118        result = 1;
119    } else {
120        numer += denom;
121    }
122
123    // Now fall into our switch statement if there are more bits to compute
124    if (bits > 0) {
125        // make room for the rest of the answer bits
126        result <<= bits;
127        switch (bits) {
128        case 6:
129            if ((numer = (numer << 1) - denom) >= 0)
130                result |= 32;
131            else
132                numer += denom;
133        case 5:
134            if ((numer = (numer << 1) - denom) >= 0)
135                result |= 16;
136            else
137                numer += denom;
138        case 4:
139            if ((numer = (numer << 1) - denom) >= 0)
140                result |= 8;
141            else
142                numer += denom;
143        case 3:
144            if ((numer = (numer << 1) - denom) >= 0)
145                result |= 4;
146            else
147                numer += denom;
148        case 2:
149            if ((numer = (numer << 1) - denom) >= 0)
150                result |= 2;
151            else
152                numer += denom;
153        case 1:
154        default:    // not strictly need, but makes GCC make better ARM code
155            if ((numer = (numer << 1) - denom) >= 0)
156                result |= 1;
157            else
158                numer += denom;
159        }
160    }
161    return result;
162}
163#endif
164
165// Given x,y in the first quadrant, return 0..63 for the angle [0..90]
166#ifndef SK_SCALAR_IS_FLOAT
167static unsigned atan_0_90(SkFixed y, SkFixed x) {
168#ifdef SK_DEBUG
169    {
170        static bool gOnce;
171        if (!gOnce) {
172            gOnce = true;
173            SkASSERT(div_64(55, 55) == 64);
174            SkASSERT(div_64(128, 256) == 32);
175            SkASSERT(div_64(2326528, 4685824) == 31);
176            SkASSERT(div_64(753664, 5210112) == 9);
177            SkASSERT(div_64(229376, 4882432) == 3);
178            SkASSERT(div_64(2, 64) == 2);
179            SkASSERT(div_64(1, 64) == 1);
180            // test that we handle underflow correctly
181            SkASSERT(div_64(12345, 0x54321234) == 0);
182        }
183    }
184#endif
185
186    SkASSERT(y > 0 && x > 0);
187    const uint8_t* table = build_sweep_table();
188
189    unsigned result;
190    bool swap = (x < y);
191    if (swap) {
192        // first part of the atan(v) = PI/2 - atan(1/v) identity
193        // since our div_64 and table want v <= 1, where v = y/x
194        SkTSwap<SkFixed>(x, y);
195    }
196
197    result = div_64(y, x);
198
199#ifdef SK_DEBUG
200    {
201        unsigned result2 = SkDivBits(y, x, 6);
202        SkASSERT(result2 == result ||
203                 (result == 1 && result2 == 0));
204    }
205#endif
206
207    SkASSERT(result < SK_ARRAY_COUNT(gSweepTable));
208    result = table[result];
209
210    if (swap) {
211        // complete the atan(v) = PI/2 - atan(1/v) identity
212        result = 64 - result;
213        // pin to 63
214        result -= result >> 6;
215    }
216
217    SkASSERT(result <= 63);
218    return result;
219}
220#endif
221
222//  returns angle in a circle [0..2PI) -> [0..255]
223#ifdef SK_SCALAR_IS_FLOAT
224static unsigned SkATan2_255(float y, float x) {
225    //    static const float g255Over2PI = 255 / (2 * SK_ScalarPI);
226    static const float g255Over2PI = 40.584510488433314f;
227
228    float result = sk_float_atan2(y, x);
229    if (result < 0) {
230        result += 2 * SK_ScalarPI;
231    }
232    SkASSERT(result >= 0);
233    // since our value is always >= 0, we can cast to int, which is faster than
234    // calling floorf()
235    int ir = (int)(result * g255Over2PI);
236    SkASSERT(ir >= 0 && ir <= 255);
237    return ir;
238}
239#else
240static unsigned SkATan2_255(SkFixed y, SkFixed x) {
241    if (x == 0) {
242        if (y == 0) {
243            return 0;
244        }
245        return y < 0 ? 192 : 64;
246    }
247    if (y == 0) {
248        return x < 0 ? 128 : 0;
249    }
250
251    /*  Find the right quadrant for x,y
252        Since atan_0_90 only handles the first quadrant, we rotate x,y
253        appropriately before calling it, and then add the right amount
254        to account for the real quadrant.
255        quadrant 0 : add 0                  | x > 0 && y > 0
256        quadrant 1 : add 64 (90 degrees)    | x < 0 && y > 0
257        quadrant 2 : add 128 (180 degrees)  | x < 0 && y < 0
258        quadrant 3 : add 192 (270 degrees)  | x > 0 && y < 0
259
260        map x<0 to (1 << 6)
261        map y<0 to (3 << 6)
262        add = map_x ^ map_y
263    */
264    int xsign = x >> 31;
265    int ysign = y >> 31;
266    int add = ((-xsign) ^ (ysign & 3)) << 6;
267
268#ifdef SK_DEBUG
269    if (0 == add)
270        SkASSERT(x > 0 && y > 0);
271    else if (64 == add)
272        SkASSERT(x < 0 && y > 0);
273    else if (128 == add)
274        SkASSERT(x < 0 && y < 0);
275    else if (192 == add)
276        SkASSERT(x > 0 && y < 0);
277    else
278        SkDEBUGFAIL("bad value for add");
279#endif
280
281    /*  This ^ trick makes x, y positive, and the swap<> handles quadrants
282        where we need to rotate x,y by 90 or -90
283    */
284    x = (x ^ xsign) - xsign;
285    y = (y ^ ysign) - ysign;
286    if (add & 64) {             // quads 1 or 3 need to swap x,y
287        SkTSwap<SkFixed>(x, y);
288    }
289
290    unsigned result = add + atan_0_90(y, x);
291    SkASSERT(result < 256);
292    return result;
293}
294#endif
295
296void SkSweepGradient::shadeSpan(int x, int y, SkPMColor* SK_RESTRICT dstC,
297                               int count) {
298    SkMatrix::MapXYProc proc = fDstToIndexProc;
299    const SkMatrix&     matrix = fDstToIndex;
300    const SkPMColor* SK_RESTRICT cache = this->getCache32();
301    SkPoint             srcPt;
302
303    if (fDstToIndexClass != kPerspective_MatrixClass) {
304        proc(matrix, SkIntToScalar(x) + SK_ScalarHalf,
305                     SkIntToScalar(y) + SK_ScalarHalf, &srcPt);
306        SkScalar dx, fx = srcPt.fX;
307        SkScalar dy, fy = srcPt.fY;
308
309        if (fDstToIndexClass == kFixedStepInX_MatrixClass) {
310            SkFixed storage[2];
311            (void)matrix.fixedStepInX(SkIntToScalar(y) + SK_ScalarHalf,
312                                      &storage[0], &storage[1]);
313            dx = SkFixedToScalar(storage[0]);
314            dy = SkFixedToScalar(storage[1]);
315        } else {
316            SkASSERT(fDstToIndexClass == kLinear_MatrixClass);
317            dx = matrix.getScaleX();
318            dy = matrix.getSkewY();
319        }
320
321        for (; count > 0; --count) {
322            *dstC++ = cache[SkATan2_255(fy, fx)];
323            fx += dx;
324            fy += dy;
325        }
326    } else {  // perspective case
327        for (int stop = x + count; x < stop; x++) {
328            proc(matrix, SkIntToScalar(x) + SK_ScalarHalf,
329                         SkIntToScalar(y) + SK_ScalarHalf, &srcPt);
330            *dstC++ = cache[SkATan2_255(srcPt.fY, srcPt.fX)];
331        }
332    }
333}
334
335void SkSweepGradient::shadeSpan16(int x, int y, uint16_t* SK_RESTRICT dstC,
336                                 int count) {
337    SkMatrix::MapXYProc proc = fDstToIndexProc;
338    const SkMatrix&     matrix = fDstToIndex;
339    const uint16_t* SK_RESTRICT cache = this->getCache16();
340    int                 toggle = ((x ^ y) & 1) * kDitherStride16;
341    SkPoint             srcPt;
342
343    if (fDstToIndexClass != kPerspective_MatrixClass) {
344        proc(matrix, SkIntToScalar(x) + SK_ScalarHalf,
345                     SkIntToScalar(y) + SK_ScalarHalf, &srcPt);
346        SkScalar dx, fx = srcPt.fX;
347        SkScalar dy, fy = srcPt.fY;
348
349        if (fDstToIndexClass == kFixedStepInX_MatrixClass) {
350            SkFixed storage[2];
351            (void)matrix.fixedStepInX(SkIntToScalar(y) + SK_ScalarHalf,
352                                      &storage[0], &storage[1]);
353            dx = SkFixedToScalar(storage[0]);
354            dy = SkFixedToScalar(storage[1]);
355        } else {
356            SkASSERT(fDstToIndexClass == kLinear_MatrixClass);
357            dx = matrix.getScaleX();
358            dy = matrix.getSkewY();
359        }
360
361        for (; count > 0; --count) {
362            int index = SkATan2_255(fy, fx) >> (8 - kCache16Bits);
363            *dstC++ = cache[toggle + index];
364            toggle ^= kDitherStride16;
365            fx += dx;
366            fy += dy;
367        }
368    } else {  // perspective case
369        for (int stop = x + count; x < stop; x++) {
370            proc(matrix, SkIntToScalar(x) + SK_ScalarHalf,
371                         SkIntToScalar(y) + SK_ScalarHalf, &srcPt);
372
373            int index = SkATan2_255(srcPt.fY, srcPt.fX);
374            index >>= (8 - kCache16Bits);
375            *dstC++ = cache[toggle + index];
376            toggle ^= kDitherStride16;
377        }
378    }
379}
380
381/////////////////////////////////////////////////////////////////////
382
383#if SK_SUPPORT_GPU
384
385class GrGLSweepGradient : public GrGLGradientStage {
386public:
387
388    GrGLSweepGradient(const GrProgramStageFactory& factory,
389                      const GrCustomStage&) : INHERITED (factory) { }
390    virtual ~GrGLSweepGradient() { }
391
392    virtual void emitVS(GrGLShaderBuilder* builder,
393                        const char* vertexCoords) SK_OVERRIDE { }
394    virtual void emitFS(GrGLShaderBuilder* builder,
395                        const char* outputColor,
396                        const char* inputColor,
397                        const char* samplerName) SK_OVERRIDE;
398
399    static StageKey GenKey(const GrCustomStage& s, const GrGLCaps& caps) { return 0; }
400
401private:
402
403    typedef GrGLGradientStage INHERITED;
404
405};
406
407/////////////////////////////////////////////////////////////////////
408
409class GrSweepGradient : public GrGradientEffect {
410public:
411
412    GrSweepGradient(GrContext* ctx,
413                    const SkSweepGradient& shader,
414                    GrSamplerState* sampler)
415    : INHERITED(ctx, shader, sampler) { }
416    virtual ~GrSweepGradient() { }
417
418    static const char* Name() { return "Sweep Gradient"; }
419    virtual const GrProgramStageFactory& getFactory() const SK_OVERRIDE {
420        return GrTProgramStageFactory<GrSweepGradient>::getInstance();
421    }
422
423    typedef GrGLSweepGradient GLProgramStage;
424
425private:
426    GR_DECLARE_CUSTOM_STAGE_TEST;
427
428    typedef GrGradientEffect INHERITED;
429};
430
431/////////////////////////////////////////////////////////////////////
432
433GR_DEFINE_CUSTOM_STAGE_TEST(GrSweepGradient);
434
435GrCustomStage* GrSweepGradient::TestCreate(SkRandom* random,
436                                           GrContext* context,
437                                           GrTexture**) {
438    SkPoint center = {random->nextUScalar1(), random->nextUScalar1()};
439
440    SkColor colors[kMaxRandomGradientColors];
441    SkScalar stopsArray[kMaxRandomGradientColors];
442    SkScalar* stops = stopsArray;
443    SkShader::TileMode tmIgnored;
444    int colorCount = RandomGradientParams(random, colors, &stops, &tmIgnored);
445    SkAutoTUnref<SkShader> shader(SkGradientShader::CreateSweep(center.fX, center.fY,
446                                                                colors, stops, colorCount));
447    GrSamplerState sampler;
448    GrCustomStage* stage = shader->asNewCustomStage(context, &sampler);
449    GrAssert(NULL != stage);
450    return stage;
451}
452
453/////////////////////////////////////////////////////////////////////
454
455void GrGLSweepGradient::emitFS(GrGLShaderBuilder* builder,
456                              const char* outputColor,
457                              const char* inputColor,
458                              const char* samplerName) {
459    SkString t;
460    t.printf("atan(- %s.y, - %s.x) * 0.1591549430918 + 0.5",
461        builder->defaultTexCoordsName(), builder->defaultTexCoordsName());
462    this->emitColorLookup(builder, t.c_str(), outputColor, inputColor, samplerName);
463}
464
465/////////////////////////////////////////////////////////////////////
466
467GrCustomStage* SkSweepGradient::asNewCustomStage(GrContext* context,
468    GrSamplerState* sampler) const {
469    sampler->matrix()->preConcat(fPtsToUnit);
470    sampler->textureParams()->setTileModeX(fTileMode);
471    sampler->textureParams()->setTileModeY(kClamp_TileMode);
472    sampler->textureParams()->setBilerp(true);
473    return SkNEW_ARGS(GrSweepGradient, (context, *this, sampler));
474}
475
476#else
477
478GrCustomStage* SkSweepGradient::asNewCustomStage(GrContext* context,
479    GrSamplerState* sampler) const {
480    SkDEBUGFAIL("Should not call in GPU-less build");
481    return NULL;
482}
483
484#endif
485