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QFontEngineFT: Revise the legacy LCD filter implementation 

Use an optimized version of the intra-pixel filter found
in FreeType's _ft_lcd_filter_legacy().
Gives us somewhat better accuracy and better performance.

Change-Id: Id4200b67e6ff55f605037c3e5464fef8bb03fbde
Reviewed-by: Friedemann Kleint <Friedemann.Kleint@theqtcompany.com>
Reviewed-by: Lars Knoll <lars.knoll@theqtcompany.com>
Reviewed-by: Eskil Abrahamsen Blomfeldt <eskil.abrahamsen-blomfeldt@theqtcompany.com>
bb10
Konstantin Ritt 2015-11-09 01:21:24 +04:00
parent a856c4a902
commit 6a7155997b
1 changed files with 15 additions and 22 deletions
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37
src/gui/text/qfontengine_ft.cpp
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@ -534,25 +534,18 @@ QFontEngineFT::Glyph::~Glyph()
delete [] data;
}
static const uint subpixel_filter[3][3] = {
{ 180, 60, 16 },
{ 38, 180, 38 },
{ 16, 60, 180 }
};
static inline uint filterPixel(uint red, uint green, uint blue, bool legacyFilter)
static inline uint filterPixel(uchar red, uchar green, uchar blue, bool legacyFilter)
{
uint res;
if (legacyFilter) {
uint high = (red*subpixel_filter[0][0] + green*subpixel_filter[0][1] + blue*subpixel_filter[0][2]) >> 8;
uint mid = (red*subpixel_filter[1][0] + green*subpixel_filter[1][1] + blue*subpixel_filter[1][2]) >> 8;
uint low = (red*subpixel_filter[2][0] + green*subpixel_filter[2][1] + blue*subpixel_filter[2][2]) >> 8;
res = (mid << 24) + (high << 16) + (mid << 8) + low;
} else {
uint alpha = green;
res = (alpha << 24) + (red << 16) + (green << 8) + blue;
uint r = red, g = green, b = blue;
// intra-pixel filter used by the legacy filter (adopted from _ft_lcd_filter_legacy)
red = (r * uint(65538 * 9/13) + g * uint(65538 * 1/6) + b * uint(65538 * 1/13)) / 65536;
green = (r * uint(65538 * 3/13) + g * uint(65538 * 4/6) + b * uint(65538 * 3/13)) / 65536;
blue = (r * uint(65538 * 1/13) + g * uint(65538 * 1/6) + b * uint(65538 * 9/13)) / 65536;
}
return res;
// alpha = green
return (green << 24) + (red << 16) + (green << 8) + blue;
}
static void convertRGBToARGB(const uchar *src, uint *dst, int width, int height, int src_pitch, bool bgr, bool legacyFilter)
@ -563,9 +556,9 @@ static void convertRGBToARGB(const uchar *src, uint *dst, int width, int height,
while (h--) {
uint *dd = dst;
for (int x = 0; x < w; x += 3) {
uint red = src[x+1-offs];
uint green = src[x+1];
uint blue = src[x+1+offs];
uchar red = src[x + 1 - offs];
uchar green = src[x + 1];
uchar blue = src[x + 1 + offs];
*dd = filterPixel(red, green, blue, legacyFilter);
++dd;
}
@ -580,9 +573,9 @@ static void convertRGBToARGB_V(const uchar *src, uint *dst, int width, int heigh
const int offs = bgr ? -src_pitch : src_pitch;
while (h--) {
for (int x = 0; x < width; x++) {
uint red = src[x+src_pitch-offs];
uint green = src[x+src_pitch];
uint blue = src[x+src_pitch+offs];
uchar red = src[x + src_pitch - offs];
uchar green = src[x + src_pitch];
uchar blue = src[x + src_pitch + offs];
dst[x] = filterPixel(red, green, blue, legacyFilter);
}
dst += width;