/*
* Copyright 2009 The Android Open Source Project
*
* Use of this source code is governed by a BSD-style license that can be
* found in the LICENSE file.
*/
#include <emmintrin.h>
#include "SkBitmapProcState_opts_SSE2.h"
#include "SkBitmapProcState_utils.h"
#include "SkColorPriv.h"
#include "SkPaint.h"
#include "SkUtils.h"
void S32_opaque_D32_filter_DX_SSE2(const SkBitmapProcState& s,
const uint32_t* xy,
int count, uint32_t* colors) {
SkASSERT(count > 0 && colors != nullptr);
SkASSERT(s.fFilterQuality != kNone_SkFilterQuality);
SkASSERT(kN32_SkColorType == s.fPixmap.colorType());
SkASSERT(s.fAlphaScale == 256);
const char* srcAddr = static_cast<const char*>(s.fPixmap.addr());
size_t rb = s.fPixmap.rowBytes();
uint32_t XY = *xy++;
unsigned y0 = XY >> 14;
const uint32_t* row0 = reinterpret_cast<const uint32_t*>(srcAddr + (y0 >> 4) * rb);
const uint32_t* row1 = reinterpret_cast<const uint32_t*>(srcAddr + (XY & 0x3FFF) * rb);
unsigned subY = y0 & 0xF;
// ( 0, 0, 0, 0, 0, 0, 0, 16)
__m128i sixteen = _mm_cvtsi32_si128(16);
// ( 0, 0, 0, 0, 16, 16, 16, 16)
sixteen = _mm_shufflelo_epi16(sixteen, 0);
// ( 0, 0, 0, 0, 0, 0, 0, y)
__m128i allY = _mm_cvtsi32_si128(subY);
// ( 0, 0, 0, 0, y, y, y, y)
allY = _mm_shufflelo_epi16(allY, 0);
// ( 0, 0, 0, 0, 16-y, 16-y, 16-y, 16-y)
__m128i negY = _mm_sub_epi16(sixteen, allY);
// (16-y, 16-y, 16-y, 16-y, y, y, y, y)
allY = _mm_unpacklo_epi64(allY, negY);
// (16, 16, 16, 16, 16, 16, 16, 16 )
sixteen = _mm_shuffle_epi32(sixteen, 0);
// ( 0, 0, 0, 0, 0, 0, 0, 0)
__m128i zero = _mm_setzero_si128();
do {
uint32_t XX = *xy++; // x0:14 | 4 | x1:14
unsigned x0 = XX >> 18;
unsigned x1 = XX & 0x3FFF;
// (0, 0, 0, 0, 0, 0, 0, x)
__m128i allX = _mm_cvtsi32_si128((XX >> 14) & 0x0F);
// (0, 0, 0, 0, x, x, x, x)
allX = _mm_shufflelo_epi16(allX, 0);
// (x, x, x, x, x, x, x, x)
allX = _mm_shuffle_epi32(allX, 0);
// (16-x, 16-x, 16-x, 16-x, 16-x, 16-x, 16-x)
__m128i negX = _mm_sub_epi16(sixteen, allX);
// Load 4 samples (pixels).
__m128i a00 = _mm_cvtsi32_si128(row0[x0]);
__m128i a01 = _mm_cvtsi32_si128(row0[x1]);
__m128i a10 = _mm_cvtsi32_si128(row1[x0]);
__m128i a11 = _mm_cvtsi32_si128(row1[x1]);
// (0, 0, a00, a10)
__m128i a00a10 = _mm_unpacklo_epi32(a10, a00);
// Expand to 16 bits per component.
a00a10 = _mm_unpacklo_epi8(a00a10, zero);
// ((a00 * (16-y)), (a10 * y)).
a00a10 = _mm_mullo_epi16(a00a10, allY);
// (a00 * (16-y) * (16-x), a10 * y * (16-x)).
a00a10 = _mm_mullo_epi16(a00a10, negX);
// (0, 0, a01, a10)
__m128i a01a11 = _mm_unpacklo_epi32(a11, a01);
// Expand to 16 bits per component.
a01a11 = _mm_unpacklo_epi8(a01a11, zero);
// (a01 * (16-y)), (a11 * y)
a01a11 = _mm_mullo_epi16(a01a11, allY);
// (a01 * (16-y) * x), (a11 * y * x)
a01a11 = _mm_mullo_epi16(a01a11, allX);
// (a00*w00 + a01*w01, a10*w10 + a11*w11)
__m128i sum = _mm_add_epi16(a00a10, a01a11);
// (DC, a00*w00 + a01*w01)
__m128i shifted = _mm_shuffle_epi32(sum, 0xEE);
// (DC, a00*w00 + a01*w01 + a10*w10 + a11*w11)
sum = _mm_add_epi16(sum, shifted);
// Divide each 16 bit component by 256.
sum = _mm_srli_epi16(sum, 8);
// Pack lower 4 16 bit values of sum into lower 4 bytes.
sum = _mm_packus_epi16(sum, zero);
// Extract low int and store.
*colors++ = _mm_cvtsi128_si32(sum);
} while (--count > 0);
}
void S32_alpha_D32_filter_DX_SSE2(const SkBitmapProcState& s,
const uint32_t* xy,
int count, uint32_t* colors) {
SkASSERT(count > 0 && colors != nullptr);
SkASSERT(s.fFilterQuality != kNone_SkFilterQuality);
SkASSERT(kN32_SkColorType == s.fPixmap.colorType());
SkASSERT(s.fAlphaScale < 256);
const char* srcAddr = static_cast<const char*>(s.fPixmap.addr());
size_t rb = s.fPixmap.rowBytes();
uint32_t XY = *xy++;
unsigned y0 = XY >> 14;
const uint32_t* row0 = reinterpret_cast<const uint32_t*>(srcAddr + (y0 >> 4) * rb);
const uint32_t* row1 = reinterpret_cast<const uint32_t*>(srcAddr + (XY & 0x3FFF) * rb);
unsigned subY = y0 & 0xF;
// ( 0, 0, 0, 0, 0, 0, 0, 16)
__m128i sixteen = _mm_cvtsi32_si128(16);
// ( 0, 0, 0, 0, 16, 16, 16, 16)
sixteen = _mm_shufflelo_epi16(sixteen, 0);
// ( 0, 0, 0, 0, 0, 0, 0, y)
__m128i allY = _mm_cvtsi32_si128(subY);
// ( 0, 0, 0, 0, y, y, y, y)
allY = _mm_shufflelo_epi16(allY, 0);
// ( 0, 0, 0, 0, 16-y, 16-y, 16-y, 16-y)
__m128i negY = _mm_sub_epi16(sixteen, allY);
// (16-y, 16-y, 16-y, 16-y, y, y, y, y)
allY = _mm_unpacklo_epi64(allY, negY);
// (16, 16, 16, 16, 16, 16, 16, 16 )
sixteen = _mm_shuffle_epi32(sixteen, 0);
// ( 0, 0, 0, 0, 0, 0, 0, 0)
__m128i zero = _mm_setzero_si128();
// ( alpha, alpha, alpha, alpha, alpha, alpha, alpha, alpha )
__m128i alpha = _mm_set1_epi16(s.fAlphaScale);
do {
uint32_t XX = *xy++; // x0:14 | 4 | x1:14
unsigned x0 = XX >> 18;
unsigned x1 = XX & 0x3FFF;
// (0, 0, 0, 0, 0, 0, 0, x)
__m128i allX = _mm_cvtsi32_si128((XX >> 14) & 0x0F);
// (0, 0, 0, 0, x, x, x, x)
allX = _mm_shufflelo_epi16(allX, 0);
// (x, x, x, x, x, x, x, x)
allX = _mm_shuffle_epi32(allX, 0);
// (16-x, 16-x, 16-x, 16-x, 16-x, 16-x, 16-x)
__m128i negX = _mm_sub_epi16(sixteen, allX);
// Load 4 samples (pixels).
__m128i a00 = _mm_cvtsi32_si128(row0[x0]);
__m128i a01 = _mm_cvtsi32_si128(row0[x1]);
__m128i a10 = _mm_cvtsi32_si128(row1[x0]);
__m128i a11 = _mm_cvtsi32_si128(row1[x1]);
// (0, 0, a00, a10)
__m128i a00a10 = _mm_unpacklo_epi32(a10, a00);
// Expand to 16 bits per component.
a00a10 = _mm_unpacklo_epi8(a00a10, zero);
// ((a00 * (16-y)), (a10 * y)).
a00a10 = _mm_mullo_epi16(a00a10, allY);
// (a00 * (16-y) * (16-x), a10 * y * (16-x)).
a00a10 = _mm_mullo_epi16(a00a10, negX);
// (0, 0, a01, a10)
__m128i a01a11 = _mm_unpacklo_epi32(a11, a01);
// Expand to 16 bits per component.
a01a11 = _mm_unpacklo_epi8(a01a11, zero);
// (a01 * (16-y)), (a11 * y)
a01a11 = _mm_mullo_epi16(a01a11, allY);
// (a01 * (16-y) * x), (a11 * y * x)
a01a11 = _mm_mullo_epi16(a01a11, allX);
// (a00*w00 + a01*w01, a10*w10 + a11*w11)
__m128i sum = _mm_add_epi16(a00a10, a01a11);
// (DC, a00*w00 + a01*w01)
__m128i shifted = _mm_shuffle_epi32(sum, 0xEE);
// (DC, a00*w00 + a01*w01 + a10*w10 + a11*w11)
sum = _mm_add_epi16(sum, shifted);
// Divide each 16 bit component by 256.
sum = _mm_srli_epi16(sum, 8);
// Multiply by alpha.
sum = _mm_mullo_epi16(sum, alpha);
// Divide each 16 bit component by 256.
sum = _mm_srli_epi16(sum, 8);
// Pack lower 4 16 bit values of sum into lower 4 bytes.
sum = _mm_packus_epi16(sum, zero);
// Extract low int and store.
*colors++ = _mm_cvtsi128_si32(sum);
} while (--count > 0);
}
static inline uint32_t ClampX_ClampY_pack_filter(SkFixed f, unsigned max,
SkFixed one) {
unsigned i = SkClampMax(f >> 16, max);
i = (i << 4) | ((f >> 12) & 0xF);
return (i << 14) | SkClampMax((f + one) >> 16, max);
}
/* SSE version of ClampX_ClampY_filter_scale()
* portable version is in core/SkBitmapProcState_matrix.h
*/
void ClampX_ClampY_filter_scale_SSE2(const SkBitmapProcState& s, uint32_t xy[],
int count, int x, int y) {
SkASSERT((s.fInvType & ~(SkMatrix::kTranslate_Mask |
SkMatrix::kScale_Mask)) == 0);
SkASSERT(s.fInvKy == 0);
const unsigned maxX = s.fPixmap.width() - 1;
const SkFixed one = s.fFilterOneX;
const SkFixed dx = s.fInvSx;
const SkBitmapProcStateAutoMapper mapper(s, x, y);
const SkFixed fy = mapper.fixedY();
const unsigned maxY = s.fPixmap.height() - 1;
// compute our two Y values up front
*xy++ = ClampX_ClampY_pack_filter(fy, maxY, s.fFilterOneY);
// now initialize fx
SkFixed fx = mapper.fixedX();
// test if we don't need to apply the tile proc
if (can_truncate_to_fixed_for_decal(fx, dx, count, maxX)) {
if (count >= 4) {
// SSE version of decal_filter_scale
while ((size_t(xy) & 0x0F) != 0) {
SkASSERT((fx >> (16 + 14)) == 0);
*xy++ = (fx >> 12 << 14) | ((fx >> 16) + 1);
fx += dx;
count--;
}
__m128i wide_1 = _mm_set1_epi32(1);
__m128i wide_dx4 = _mm_set1_epi32(dx * 4);
__m128i wide_fx = _mm_set_epi32(fx + dx * 3, fx + dx * 2,
fx + dx, fx);
while (count >= 4) {
__m128i wide_out;
wide_out = _mm_slli_epi32(_mm_srai_epi32(wide_fx, 12), 14);
wide_out = _mm_or_si128(wide_out, _mm_add_epi32(
_mm_srai_epi32(wide_fx, 16), wide_1));
_mm_store_si128(reinterpret_cast<__m128i*>(xy), wide_out);
xy += 4;
fx += dx * 4;
wide_fx = _mm_add_epi32(wide_fx, wide_dx4);
count -= 4;
} // while count >= 4
} // if count >= 4
while (count-- > 0) {
SkASSERT((fx >> (16 + 14)) == 0);
*xy++ = (fx >> 12 << 14) | ((fx >> 16) + 1);
fx += dx;
}
} else {
// SSE2 only support 16bit interger max & min, so only process the case
// maxX less than the max 16bit interger. Actually maxX is the bitmap's
// height, there should be rare bitmap whose height will be greater
// than max 16bit interger in the real world.
if ((count >= 4) && (maxX <= 0xFFFF)) {
while (((size_t)xy & 0x0F) != 0) {
*xy++ = ClampX_ClampY_pack_filter(fx, maxX, one);
fx += dx;
count--;
}
__m128i wide_fx = _mm_set_epi32(fx + dx * 3, fx + dx * 2,
fx + dx, fx);
__m128i wide_dx4 = _mm_set1_epi32(dx * 4);
__m128i wide_one = _mm_set1_epi32(one);
__m128i wide_maxX = _mm_set1_epi32(maxX);
__m128i wide_mask = _mm_set1_epi32(0xF);
while (count >= 4) {
__m128i wide_i;
__m128i wide_lo;
__m128i wide_fx1;
// i = SkClampMax(f>>16,maxX)
wide_i = _mm_max_epi16(_mm_srli_epi32(wide_fx, 16),
_mm_setzero_si128());
wide_i = _mm_min_epi16(wide_i, wide_maxX);
// i<<4 | EXTRACT_LOW_BITS(fx)
wide_lo = _mm_srli_epi32(wide_fx, 12);
wide_lo = _mm_and_si128(wide_lo, wide_mask);
wide_i = _mm_slli_epi32(wide_i, 4);
wide_i = _mm_or_si128(wide_i, wide_lo);
// i<<14
wide_i = _mm_slli_epi32(wide_i, 14);
// SkClampMax(((f+one))>>16,max)
wide_fx1 = _mm_add_epi32(wide_fx, wide_one);
wide_fx1 = _mm_max_epi16(_mm_srli_epi32(wide_fx1, 16),
_mm_setzero_si128());
wide_fx1 = _mm_min_epi16(wide_fx1, wide_maxX);
// final combination
wide_i = _mm_or_si128(wide_i, wide_fx1);
_mm_store_si128(reinterpret_cast<__m128i*>(xy), wide_i);
wide_fx = _mm_add_epi32(wide_fx, wide_dx4);
fx += dx * 4;
xy += 4;
count -= 4;
} // while count >= 4
} // if count >= 4
while (count-- > 0) {
*xy++ = ClampX_ClampY_pack_filter(fx, maxX, one);
fx += dx;
}
}
}
/* SSE version of ClampX_ClampY_nofilter_scale()
* portable version is in core/SkBitmapProcState_matrix.h
*/
void ClampX_ClampY_nofilter_scale_SSE2(const SkBitmapProcState& s,
uint32_t xy[], int count, int x, int y) {
SkASSERT((s.fInvType & ~(SkMatrix::kTranslate_Mask |
SkMatrix::kScale_Mask)) == 0);
// we store y, x, x, x, x, x
const unsigned maxX = s.fPixmap.width() - 1;
const SkBitmapProcStateAutoMapper mapper(s, x, y);
const unsigned maxY = s.fPixmap.height() - 1;
*xy++ = SkClampMax(mapper.intY(), maxY);
SkFixed fx = mapper.fixedX();
if (0 == maxX) {
// all of the following X values must be 0
memset(xy, 0, count * sizeof(uint16_t));
return;
}
const SkFixed dx = s.fInvSx;
// test if we don't need to apply the tile proc
if ((unsigned)(fx >> 16) <= maxX &&
(unsigned)((fx + dx * (count - 1)) >> 16) <= maxX) {
// SSE version of decal_nofilter_scale
if (count >= 8) {
while (((size_t)xy & 0x0F) != 0) {
*xy++ = pack_two_shorts(fx >> 16, (fx + dx) >> 16);
fx += 2 * dx;
count -= 2;
}
__m128i wide_dx4 = _mm_set1_epi32(dx * 4);
__m128i wide_dx8 = _mm_add_epi32(wide_dx4, wide_dx4);
__m128i wide_low = _mm_set_epi32(fx + dx * 3, fx + dx * 2,
fx + dx, fx);
__m128i wide_high = _mm_add_epi32(wide_low, wide_dx4);
while (count >= 8) {
__m128i wide_out_low = _mm_srli_epi32(wide_low, 16);
__m128i wide_out_high = _mm_srli_epi32(wide_high, 16);
__m128i wide_result = _mm_packs_epi32(wide_out_low,
wide_out_high);
_mm_store_si128(reinterpret_cast<__m128i*>(xy), wide_result);
wide_low = _mm_add_epi32(wide_low, wide_dx8);
wide_high = _mm_add_epi32(wide_high, wide_dx8);
xy += 4;
fx += dx * 8;
count -= 8;
}
} // if count >= 8
uint16_t* xx = reinterpret_cast<uint16_t*>(xy);
while (count-- > 0) {
*xx++ = SkToU16(fx >> 16);
fx += dx;
}
} else {
// SSE2 only support 16bit interger max & min, so only process the case
// maxX less than the max 16bit interger. Actually maxX is the bitmap's
// height, there should be rare bitmap whose height will be greater
// than max 16bit interger in the real world.
if ((count >= 8) && (maxX <= 0xFFFF)) {
while (((size_t)xy & 0x0F) != 0) {
*xy++ = pack_two_shorts(SkClampMax((fx + dx) >> 16, maxX),
SkClampMax(fx >> 16, maxX));
fx += 2 * dx;
count -= 2;
}
__m128i wide_dx4 = _mm_set1_epi32(dx * 4);
__m128i wide_dx8 = _mm_add_epi32(wide_dx4, wide_dx4);
__m128i wide_low = _mm_set_epi32(fx + dx * 3, fx + dx * 2,
fx + dx, fx);
__m128i wide_high = _mm_add_epi32(wide_low, wide_dx4);
__m128i wide_maxX = _mm_set1_epi32(maxX);
while (count >= 8) {
__m128i wide_out_low = _mm_srli_epi32(wide_low, 16);
__m128i wide_out_high = _mm_srli_epi32(wide_high, 16);
wide_out_low = _mm_max_epi16(wide_out_low,
_mm_setzero_si128());
wide_out_low = _mm_min_epi16(wide_out_low, wide_maxX);
wide_out_high = _mm_max_epi16(wide_out_high,
_mm_setzero_si128());
wide_out_high = _mm_min_epi16(wide_out_high, wide_maxX);
__m128i wide_result = _mm_packs_epi32(wide_out_low,
wide_out_high);
_mm_store_si128(reinterpret_cast<__m128i*>(xy), wide_result);
wide_low = _mm_add_epi32(wide_low, wide_dx8);
wide_high = _mm_add_epi32(wide_high, wide_dx8);
xy += 4;
fx += dx * 8;
count -= 8;
}
} // if count >= 8
uint16_t* xx = reinterpret_cast<uint16_t*>(xy);
while (count-- > 0) {
*xx++ = SkClampMax(fx >> 16, maxX);
fx += dx;
}
}
}
/* SSE version of ClampX_ClampY_filter_affine()
* portable version is in core/SkBitmapProcState_matrix.h
*/
void ClampX_ClampY_filter_affine_SSE2(const SkBitmapProcState& s,
uint32_t xy[], int count, int x, int y) {
const SkBitmapProcStateAutoMapper mapper(s, x, y);
SkFixed oneX = s.fFilterOneX;
SkFixed oneY = s.fFilterOneY;
SkFixed fx = mapper.fixedX();
SkFixed fy = mapper.fixedY();
SkFixed dx = s.fInvSx;
SkFixed dy = s.fInvKy;
unsigned maxX = s.fPixmap.width() - 1;
unsigned maxY = s.fPixmap.height() - 1;
if (count >= 2 && (maxX <= 0xFFFF)) {
SkFixed dx2 = dx + dx;
SkFixed dy2 = dy + dy;
__m128i wide_f = _mm_set_epi32(fx + dx, fy + dy, fx, fy);
__m128i wide_d2 = _mm_set_epi32(dx2, dy2, dx2, dy2);
__m128i wide_one = _mm_set_epi32(oneX, oneY, oneX, oneY);
__m128i wide_max = _mm_set_epi32(maxX, maxY, maxX, maxY);
__m128i wide_mask = _mm_set1_epi32(0xF);
while (count >= 2) {
// i = SkClampMax(f>>16,maxX)
__m128i wide_i = _mm_max_epi16(_mm_srli_epi32(wide_f, 16),
_mm_setzero_si128());
wide_i = _mm_min_epi16(wide_i, wide_max);
// i<<4 | EXTRACT_LOW_BITS(f)
__m128i wide_lo = _mm_srli_epi32(wide_f, 12);
wide_lo = _mm_and_si128(wide_lo, wide_mask);
wide_i = _mm_slli_epi32(wide_i, 4);
wide_i = _mm_or_si128(wide_i, wide_lo);
// i<<14
wide_i = _mm_slli_epi32(wide_i, 14);
// SkClampMax(((f+one))>>16,max)
__m128i wide_f1 = _mm_add_epi32(wide_f, wide_one);
wide_f1 = _mm_max_epi16(_mm_srli_epi32(wide_f1, 16),
_mm_setzero_si128());
wide_f1 = _mm_min_epi16(wide_f1, wide_max);
// final combination
wide_i = _mm_or_si128(wide_i, wide_f1);
_mm_storeu_si128(reinterpret_cast<__m128i*>(xy), wide_i);
wide_f = _mm_add_epi32(wide_f, wide_d2);
fx += dx2;
fy += dy2;
xy += 4;
count -= 2;
} // while count >= 2
} // if count >= 2
while (count-- > 0) {
*xy++ = ClampX_ClampY_pack_filter(fy, maxY, oneY);
fy += dy;
*xy++ = ClampX_ClampY_pack_filter(fx, maxX, oneX);
fx += dx;
}
}
/* SSE version of ClampX_ClampY_nofilter_affine()
* portable version is in core/SkBitmapProcState_matrix.h
*/
void ClampX_ClampY_nofilter_affine_SSE2(const SkBitmapProcState& s,
uint32_t xy[], int count, int x, int y) {
SkASSERT(s.fInvType & SkMatrix::kAffine_Mask);
SkASSERT((s.fInvType & ~(SkMatrix::kTranslate_Mask |
SkMatrix::kScale_Mask |
SkMatrix::kAffine_Mask)) == 0);
const SkBitmapProcStateAutoMapper mapper(s, x, y);
SkFixed fx = mapper.fixedX();
SkFixed fy = mapper.fixedY();
SkFixed dx = s.fInvSx;
SkFixed dy = s.fInvKy;
int maxX = s.fPixmap.width() - 1;
int maxY = s.fPixmap.height() - 1;
if (count >= 4 && (maxX <= 0xFFFF)) {
while (((size_t)xy & 0x0F) != 0) {
*xy++ = (SkClampMax(fy >> 16, maxY) << 16) |
SkClampMax(fx >> 16, maxX);
fx += dx;
fy += dy;
count--;
}
SkFixed dx4 = dx * 4;
SkFixed dy4 = dy * 4;
__m128i wide_fx = _mm_set_epi32(fx + dx * 3, fx + dx * 2,
fx + dx, fx);
__m128i wide_fy = _mm_set_epi32(fy + dy * 3, fy + dy * 2,
fy + dy, fy);
__m128i wide_dx4 = _mm_set1_epi32(dx4);
__m128i wide_dy4 = _mm_set1_epi32(dy4);
__m128i wide_maxX = _mm_set1_epi32(maxX);
__m128i wide_maxY = _mm_set1_epi32(maxY);
while (count >= 4) {
// SkClampMax(fx>>16,maxX)
__m128i wide_lo = _mm_max_epi16(_mm_srli_epi32(wide_fx, 16),
_mm_setzero_si128());
wide_lo = _mm_min_epi16(wide_lo, wide_maxX);
// SkClampMax(fy>>16,maxY)
__m128i wide_hi = _mm_max_epi16(_mm_srli_epi32(wide_fy, 16),
_mm_setzero_si128());
wide_hi = _mm_min_epi16(wide_hi, wide_maxY);
// final combination
__m128i wide_i = _mm_or_si128(_mm_slli_epi32(wide_hi, 16),
wide_lo);
_mm_store_si128(reinterpret_cast<__m128i*>(xy), wide_i);
wide_fx = _mm_add_epi32(wide_fx, wide_dx4);
wide_fy = _mm_add_epi32(wide_fy, wide_dy4);
fx += dx4;
fy += dy4;
xy += 4;
count -= 4;
} // while count >= 4
} // if count >= 4
while (count-- > 0) {
*xy++ = (SkClampMax(fy >> 16, maxY) << 16) |
SkClampMax(fx >> 16, maxX);
fx += dx;
fy += dy;
}
}