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Some initial optimization work on RGB converter.
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Unrolled loop once so we don't have to read the same pb and pr array elements
twice, and moved some variables out of the inner loop. Now a little less than
2x as fast as before!

Note that this was about 4x as slow as the YV12 output, now it's about 2x as
slow.  :)
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@icculus
icculus committed Apr 29, 2018
1 parent 7547fbf commit ce771c8
Showing 1 changed file with 38 additions and 22 deletions.
60 changes: 38 additions & 22 deletions theoraplay_cvtrgb.h
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Expand Up @@ -15,7 +15,21 @@ static unsigned char *THEORAPLAY_CVT_FNNAME_420(const th_info *tinfo,
{
const int w = tinfo->pic_width;
const int h = tinfo->pic_height;
const int halfw = w / 2;
unsigned char *pixels = (unsigned char *) malloc(w * h * 4);

// http://www.theora.org/doc/Theora.pdf, 1.1 spec,
// chapter 4.2 (Y'CbCr -> Y'PbPr -> R'G'B')
// These constants apparently work for NTSC _and_ PAL/SECAM.
const float yoffset = 16.0f;
const float yexcursion = 219.0f;
const float cboffset = 128.0f;
const float cbexcursion = 224.0f;
const float croffset = 128.0f;
const float crexcursion = 224.0f;
const float kr = 0.299f;
const float kb = 0.114f;

if (pixels)
{
unsigned char *dst = pixels;
Expand All @@ -27,34 +41,36 @@ static unsigned char *THEORAPLAY_CVT_FNNAME_420(const th_info *tinfo,
const unsigned char *py = ycbcr[0].data + yoff;
const unsigned char *pcb = ycbcr[1].data + cboff;
const unsigned char *pcr = ycbcr[2].data + cboff;
int posx, posy;
int posy;

for (posy = 0; posy < h; posy++)
{
for (posx = 0; posx < w; posx++)
int posx, poshalfx;

posx = 0;
for (poshalfx = 0; poshalfx < halfw; poshalfx++, posx += 2)
{
// http://www.theora.org/doc/Theora.pdf, 1.1 spec,
// chapter 4.2 (Y'CbCr -> Y'PbPr -> R'G'B')
// These constants apparently work for NTSC _and_ PAL/SECAM.
const float yoffset = 16.0f;
const float yexcursion = 219.0f;
const float cboffset = 128.0f;
const float cbexcursion = 224.0f;
const float croffset = 128.0f;
const float crexcursion = 224.0f;
const float kr = 0.299f;
const float kb = 0.114f;
const float y1 = (((float) py[posx]) - yoffset) / yexcursion;
const float y2 = (((float) py[posx+1]) - yoffset) / yexcursion;
const float pb = (((float) pcb[poshalfx]) - cboffset) / cbexcursion;
const float pr = (((float) pcr[poshalfx]) - croffset) / crexcursion;
const float r1 = (y1 + (2.0f * (1.0f - kr) * pr)) * 255.0f;
const float g1 = (y1 - ((2.0f * (((1.0f - kb) * kb) / ((1.0f - kb) - kr))) * pb) - ((2.0f * (((1.0f - kr) * kr) / ((1.0f - kb) - kr))) * pr)) * 255.0f;
const float b1 = (y1 + (2.0f * (1.0f - kb) * pb)) * 255.0f;
const float r2 = (y2 + (2.0f * (1.0f - kr) * pr)) * 255.0f;
const float g2 = (y2 - ((2.0f * (((1.0f - kb) * kb) / ((1.0f - kb) - kr))) * pb) - ((2.0f * (((1.0f - kr) * kr) / ((1.0f - kb) - kr))) * pr)) * 255.0f;
const float b2 = (y2 + (2.0f * (1.0f - kb) * pb)) * 255.0f;

const float y = (((float) py[posx]) - yoffset) / yexcursion;
const float pb = (((float) pcb[posx / 2]) - cboffset) / cbexcursion;
const float pr = (((float) pcr[posx / 2]) - croffset) / crexcursion;
const float r = (y + (2.0f * (1.0f - kr) * pr)) * 255.0f;
const float g = (y - ((2.0f * (((1.0f - kb) * kb) / ((1.0f - kb) - kr))) * pb) - ((2.0f * (((1.0f - kr) * kr) / ((1.0f - kb) - kr))) * pr)) * 255.0f;
const float b = (y + (2.0f * (1.0f - kb) * pb)) * 255.0f;
*(dst++) = (unsigned char) ((r1 < 0.0f) ? 0.0f : (r1 > 255.0f) ? 255.0f : r1);
*(dst++) = (unsigned char) ((g1 < 0.0f) ? 0.0f : (g1 > 255.0f) ? 255.0f : g1);
*(dst++) = (unsigned char) ((b1 < 0.0f) ? 0.0f : (b1 > 255.0f) ? 255.0f : b1);
#if THEORAPLAY_CVT_RGB_ALPHA
*(dst++) = 0xFF;
#endif

*(dst++) = (unsigned char) ((r < 0.0f) ? 0.0f : (r > 255.0f) ? 255.0f : r);
*(dst++) = (unsigned char) ((g < 0.0f) ? 0.0f : (g > 255.0f) ? 255.0f : g);
*(dst++) = (unsigned char) ((b < 0.0f) ? 0.0f : (b > 255.0f) ? 255.0f : b);
*(dst++) = (unsigned char) ((r2 < 0.0f) ? 0.0f : (r2 > 255.0f) ? 255.0f : r2);
*(dst++) = (unsigned char) ((g2 < 0.0f) ? 0.0f : (g2 > 255.0f) ? 255.0f : g2);
*(dst++) = (unsigned char) ((b2 < 0.0f) ? 0.0f : (b2 > 255.0f) ? 255.0f : b2);
#if THEORAPLAY_CVT_RGB_ALPHA
*(dst++) = 0xFF;
#endif
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