SkSweepGradient.cpp revision c78188896e28a4ae49e406a7422b345ae177dafe 
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    int                 toggle = init_dither_toggle(x, y);
302    SkPoint             srcPt;
303
304    if (fDstToIndexClass != kPerspective_MatrixClass) {
305        proc(matrix, SkIntToScalar(x) + SK_ScalarHalf,
306                     SkIntToScalar(y) + SK_ScalarHalf, &srcPt);
307        SkScalar dx, fx = srcPt.fX;
308        SkScalar dy, fy = srcPt.fY;
309
310        if (fDstToIndexClass == kFixedStepInX_MatrixClass) {
311            SkFixed storage[2];
312            (void)matrix.fixedStepInX(SkIntToScalar(y) + SK_ScalarHalf,
313                                      &storage[0], &storage[1]);
314            dx = SkFixedToScalar(storage[0]);
315            dy = SkFixedToScalar(storage[1]);
316        } else {
317            SkASSERT(fDstToIndexClass == kLinear_MatrixClass);
318            dx = matrix.getScaleX();
319            dy = matrix.getSkewY();
320        }
321
322        for (; count > 0; --count) {
323            *dstC++ = cache[toggle + SkATan2_255(fy, fx)];
324            fx += dx;
325            fy += dy;
326            toggle = next_dither_toggle(toggle);
327        }
328    } else {  // perspective case
329        for (int stop = x + count; x < stop; x++) {
330            proc(matrix, SkIntToScalar(x) + SK_ScalarHalf,
331                         SkIntToScalar(y) + SK_ScalarHalf, &srcPt);
332            *dstC++ = cache[toggle + SkATan2_255(srcPt.fY, srcPt.fX)];
333            toggle = next_dither_toggle(toggle);
334        }
335    }
336}
337
338void SkSweepGradient::shadeSpan16(int x, int y, uint16_t* SK_RESTRICT dstC,
339                                 int count) {
340    SkMatrix::MapXYProc proc = fDstToIndexProc;
341    const SkMatrix&     matrix = fDstToIndex;
342    const uint16_t* SK_RESTRICT cache = this->getCache16();
343    int                 toggle = init_dither_toggle16(x, y);
344    SkPoint             srcPt;
345
346    if (fDstToIndexClass != kPerspective_MatrixClass) {
347        proc(matrix, SkIntToScalar(x) + SK_ScalarHalf,
348                     SkIntToScalar(y) + SK_ScalarHalf, &srcPt);
349        SkScalar dx, fx = srcPt.fX;
350        SkScalar dy, fy = srcPt.fY;
351
352        if (fDstToIndexClass == kFixedStepInX_MatrixClass) {
353            SkFixed storage[2];
354            (void)matrix.fixedStepInX(SkIntToScalar(y) + SK_ScalarHalf,
355                                      &storage[0], &storage[1]);
356            dx = SkFixedToScalar(storage[0]);
357            dy = SkFixedToScalar(storage[1]);
358        } else {
359            SkASSERT(fDstToIndexClass == kLinear_MatrixClass);
360            dx = matrix.getScaleX();
361            dy = matrix.getSkewY();
362        }
363
364        for (; count > 0; --count) {
365            int index = SkATan2_255(fy, fx) >> (8 - kCache16Bits);
366            *dstC++ = cache[toggle + index];
367            toggle = next_dither_toggle16(toggle);
368            fx += dx;
369            fy += dy;
370        }
371    } else {  // perspective case
372        for (int stop = x + count; x < stop; x++) {
373            proc(matrix, SkIntToScalar(x) + SK_ScalarHalf,
374                         SkIntToScalar(y) + SK_ScalarHalf, &srcPt);
375
376            int index = SkATan2_255(srcPt.fY, srcPt.fX);
377            index >>= (8 - kCache16Bits);
378            *dstC++ = cache[toggle + index];
379            toggle = next_dither_toggle16(toggle);
380        }
381    }
382}
383
384/////////////////////////////////////////////////////////////////////
385
386#if SK_SUPPORT_GPU
387
388#include "GrTBackendEffectFactory.h"
389
390class GrGLSweepGradient : public GrGLGradientEffect {
391public:
392
393    GrGLSweepGradient(const GrBackendEffectFactory& factory,
394                      const GrDrawEffect&) : INHERITED (factory) { }
395    virtual ~GrGLSweepGradient() { }
396
397    virtual void emitCode(GrGLShaderBuilder*,
398                          const GrDrawEffect&,
399                          EffectKey,
400                          const char* outputColor,
401                          const char* inputColor,
402                          const TextureSamplerArray&) SK_OVERRIDE;
403
404    static EffectKey GenKey(const GrDrawEffect& drawEffect, const GrGLCaps&) {
405        return GenMatrixKey(drawEffect);
406    }
407
408private:
409
410    typedef GrGLGradientEffect INHERITED;
411
412};
413
414/////////////////////////////////////////////////////////////////////
415
416class GrSweepGradient : public GrGradientEffect {
417public:
418    static GrEffectRef* Create(GrContext* ctx,
419                               const SkSweepGradient& shader,
420                               const SkMatrix& matrix) {
421        AutoEffectUnref effect(SkNEW_ARGS(GrSweepGradient, (ctx, shader, matrix)));
422        return CreateEffectRef(effect);
423    }
424    virtual ~GrSweepGradient() { }
425
426    static const char* Name() { return "Sweep Gradient"; }
427    virtual const GrBackendEffectFactory& getFactory() const SK_OVERRIDE {
428        return GrTBackendEffectFactory<GrSweepGradient>::getInstance();
429    }
430
431    typedef GrGLSweepGradient GLEffect;
432
433private:
434    GrSweepGradient(GrContext* ctx,
435                    const SkSweepGradient& shader,
436                    const SkMatrix& matrix)
437    : INHERITED(ctx, shader, matrix, SkShader::kClamp_TileMode) { }
438    GR_DECLARE_EFFECT_TEST;
439
440    typedef GrGradientEffect INHERITED;
441};
442
443/////////////////////////////////////////////////////////////////////
444
445GR_DEFINE_EFFECT_TEST(GrSweepGradient);
446
447GrEffectRef* GrSweepGradient::TestCreate(SkMWCRandom* random,
448                                         GrContext* context,
449                                         GrTexture**) {
450    SkPoint center = {random->nextUScalar1(), random->nextUScalar1()};
451
452    SkColor colors[kMaxRandomGradientColors];
453    SkScalar stopsArray[kMaxRandomGradientColors];
454    SkScalar* stops = stopsArray;
455    SkShader::TileMode tmIgnored;
456    int colorCount = RandomGradientParams(random, colors, &stops, &tmIgnored);
457    SkAutoTUnref<SkShader> shader(SkGradientShader::CreateSweep(center.fX, center.fY,
458                                                                colors, stops, colorCount));
459    SkPaint paint;
460    return shader->asNewEffect(context, paint);
461}
462
463/////////////////////////////////////////////////////////////////////
464
465void GrGLSweepGradient::emitCode(GrGLShaderBuilder* builder,
466                                 const GrDrawEffect&,
467                                 EffectKey key,
468                                 const char* outputColor,
469                                 const char* inputColor,
470                                 const TextureSamplerArray& samplers) {
471    this->emitYCoordUniform(builder);
472    const char* coords;
473    this->setupMatrix(builder, key, &coords);
474    SkString t;
475    t.printf("atan(- %s.y, - %s.x) * 0.1591549430918 + 0.5", coords, coords);
476    this->emitColorLookup(builder, t.c_str(), outputColor, inputColor, samplers[0]);
477}
478
479/////////////////////////////////////////////////////////////////////
480
481GrEffectRef* SkSweepGradient::asNewEffect(GrContext* context, const SkPaint&) const {
482    SkMatrix matrix;
483    if (!this->getLocalMatrix().invert(&matrix)) {
484        return NULL;
485    }
486    matrix.postConcat(fPtsToUnit);
487    return GrSweepGradient::Create(context, *this, matrix);
488}
489
490#else
491
492GrEffectRef* SkSweepGradient::asNewEffect(GrContext*, const SkPaint&) const {
493    SkDEBUGFAIL("Should not call in GPU-less build");
494    return NULL;
495}
496
497#endif
498
499#ifdef SK_DEVELOPER
500void SkSweepGradient::toString(SkString* str) const {
501    str->append("SkSweepGradient: (");
502
503    str->append("center: (");
504    str->appendScalar(fCenter.fX);
505    str->append(", ");
506    str->appendScalar(fCenter.fY);
507    str->append(") ");
508
509    this->INHERITED::toString(str);
510
511    str->append(")");
512}
513#endif
514