/modules/libpr0n/decoders/png/nsPNGDecoder.cpp
695 void
696 row_callback(png_structp png_ptr, png_bytep new_row,
697 png_uint_32 row_num, int pass)
698 {
:
:
793 case gfxIFormats::RGB_A1:
794 {
795 for (PRUint32 x=iwidth; x>0; --x) {
796 *cptr32++ = GFX_PACKED_PIXEL(line[3]?0xFF:0x00, line[0], line[1], line[2]);
797 if (line[3] == 0)
798 rowHasNoAlpha = PR_FALSE;
799 line += 4;
800 }
801 }
802 break;
803 case gfxIFormats::RGB_A8:
804 {
805 for (PRUint32 x=width; x>0; --x) {
806 *cptr32++ = GFX_PACKED_PIXEL(line[3], line[0], line[1], line[2]);
807 if (line[3] != 0xff)
808 rowHasNoAlpha = PR_FALSE;
809 line += 4;
810 }
811 }
ここで使ってる GFX_PACKED_PIXEL のマクロってどうなっているかと思ったら、
/gfx/thebes/public/gfxColor.h
118 /**
119 * Fast approximate division by 255. It has the property that
120 * for all 0 <= n <= 255*255, FAST_DIVIDE_BY_255(n) == n/255.
121 * But it only uses two adds and two shifts instead of an
122 * integer division (which is expensive on many processors).
123 *
124 * equivalent to ((v)/255)
125 */
126 #define GFX_DIVIDE_BY_255(v) \
127 (((((unsigned)(v)) << 8) + ((unsigned)(v)) + 255) >> 16)
128
129 /**
130 * Fast premultiply macro
131 *
132 * equivalent to (((c)*(a))/255)
133 */
134 #define GFX_PREMULTIPLY(c,a) GFX_DIVIDE_BY_255((c)*(a))
135
136 /**
137 * Macro to pack the 4 8-bit channels (A,R,G,B)
138 * into a 32-bit packed premultiplied pixel.
139 *
140 * The checks for 0 alpha or max alpha ensure that the
141 * compiler selects the quicked calculation when alpha is constant.
142 */
143 #define GFX_PACKED_PIXEL(a,r,g,b) \
144 ((a) == 0x00) ? 0x00000000 : \
145 ((a) == 0xFF) ? ((0xFF << 24) | ((r) << 16) | ((g) << 8) | (b)) \
146 : ((a) << 24) | \
147 (GFX_PREMULTIPLY(r,a) << 16) | \
148 (GFX_PREMULTIPLY(g,a) << 8) | \
149 (GFX_PREMULTIPLY(b,a))
だから、アルファブレンディングしたPNGを持ってくると遅すぎじゃないかな？
こんな感じのパックドコードをSSE2で実装すれば約2倍くらいは速くなるような。
xmm0080 = _mm_set1_epi16(0x0080);
xmm0101 = _mm_set1_epi16(0x0101);
xmmAlpha = _mm_set_epi32(0x00ff0000, 0x00000000, 0x00ff0000, 0x00000000);
data = _mm_loadu_si128((__m128i*)src);
dataLo = _mm_unpacklo_epi8 (data, _mm_setzero_si128 ());
dataHi = _mm_unpackhi_epi8 (data, _mm_setzero_si128 ());
alphaLo = _mm_shufflelo_epi16 (dataLo, _MM_SHUFFLE(3, 3, 3, 3));
alphaHi = _mm_shufflelo_epi16 (dataHi, _MM_SHUFFLE(3, 3, 3, 3));
alphaLo = _mm_shufflehi_epi16 (alphaLo, _MM_SHUFFLE(3, 3, 3, 3));
alphaHi = _mm_shufflehi_epi16 (alphaHi, _MM_SHUFFLE(3, 3, 3, 3));
alphaLo = _mm_or_si128(alphaLo, xmmAlpha);
alphaHi = _mm_or_si128(alphaHi, xmmAlpha);
dataLo = _mm_shufflelo_epi16 (dataLo, _MM_SHUFFLE(3, 0, 1, 2));
dataLo = _mm_shufflehi_epi16 (dataLo, _MM_SHUFFLE(3, 0, 1, 2));
dataHi = _mm_shufflelo_epi16 (dataHi, _MM_SHUFFLE(3, 0, 1, 2));
dataHi = _mm_shufflehi_epi16 (dataHi, _MM_SHUFFLE(3, 0, 1, 2));
dataLo = _mm_mullo_epi16(dataLo, alphaLo);
dataHi = _mm_mullo_epi16(dataHi, alphaHi);
dataLo = _mm_adds_epu16(dataLo, xmm0080);
dataHi = _mm_adds_epu16(dataHi, xmm0080);
dataLo = _mm_mulhi_epu16(dataLo, xmm0101);
dataHi = _mm_mulhi_epu16(dataHi, xmm0101);
data = _mm_packus_epi16 (dataLo, dataHi);
_mm_storeu_si128((__m128i*)dst, data);
今度テストしてみよう。
