Replace QDrawHelperGammaTables with QColorProfile

Turns the two set of tables in QDrawHelperGammaTables into two
QColorProfile classes that use similar structures and can be reused for
other gamma correction.

At the same time clean-up and improve the comma-correct blending code
to use the new profiles and QRgba64 precision.

Change-Id: I302bd87a5c836e1010fff6d633eeb56fd4ae2ff0
Reviewed-by: Olivier Goffart (Woboq GmbH) <ogoffart@woboq.com>

1 files changed, 48 insertions, 98 deletions

diff --git a/src/gui/painting/qdrawhelper.cpp b/src/gui/painting/qdrawhelper.cpp
index fe1ff6603d..bd853ad934 100644
--- a/src/gui/painting/qdrawhelper.cpp
+++ b/src/gui/painting/qdrawhelper.cpp
@@ -43,6 +43,7 @@
 #include <qstylehints.h>
 #include <qguiapplication.h>
 #include <qatomic.h>
+#include <private/qcolorprofile_p.h>
 #include <private/qdrawhelper_p.h>
 #include <private/qpaintengine_raster_p.h>
 #include <private/qpainter_p.h>
@@ -5508,80 +5509,35 @@ static void qt_alphamapblit_quint16(QRasterBuffer *rasterBuffer,
     }
 }
 
-static inline void rgbBlendPixel(quint32 *dst, int coverage, int sr, int sg, int sb, const uchar *gamma, const uchar *invgamma)
+static inline void rgbBlendPixel(quint32 *dst, int coverage, QRgba64 slinear, const QColorProfile *colorProfile)
 {
-    // Do a gray alphablend...
-    int da = qAlpha(*dst);
-    int dr = qRed(*dst);
-    int dg = qGreen(*dst);
-    int db = qBlue(*dst);
+    // Do a gammacorrected RGB alphablend...
+    const int mr = qRed(coverage);
+    const int mg = qGreen(coverage);
+    const int mb = qBlue(coverage);
 
-    if (da != 255
-        ) {
+    const QRgba64 dlinear = colorProfile->toLinear64(*dst);
 
-        int a = qGray(coverage);
-        sr = qt_div_255(invgamma[sr] * a);
-        sg = qt_div_255(invgamma[sg] * a);
-        sb = qt_div_255(invgamma[sb] * a);
+    QRgba64 blend;
+    blend.setAlpha(65535);
+    blend.setRed  (qt_div_255(slinear.red()   * mr + dlinear.red()   * (255 - mr)));
+    blend.setGreen(qt_div_255(slinear.green() * mg + dlinear.green() * (255 - mg)));
+    blend.setBlue (qt_div_255(slinear.blue()  * mb + dlinear.blue()  * (255 - mb)));
 
-        int ia = 255 - a;
-        dr = qt_div_255(dr * ia);
-        dg = qt_div_255(dg * ia);
-        db = qt_div_255(db * ia);
-
-        *dst = ((a + qt_div_255((255 - a) * da)) << 24)
-            |  ((sr + dr) << 16)
-            |  ((sg + dg) << 8)
-            |  ((sb + db));
-        return;
-    }
-
-    int mr = qRed(coverage);
-    int mg = qGreen(coverage);
-    int mb = qBlue(coverage);
-
-    dr = gamma[dr];
-    dg = gamma[dg];
-    db = gamma[db];
-
-    int nr = qt_div_255(sr * mr + dr * (255 - mr));
-    int ng = qt_div_255(sg * mg + dg * (255 - mg));
-    int nb = qt_div_255(sb * mb + db * (255 - mb));
-
-    nr = invgamma[nr];
-    ng = invgamma[ng];
-    nb = invgamma[nb];
-
-    *dst = qRgb(nr, ng, nb);
+    *dst = colorProfile->fromLinear64(blend);
 }
 
-#if defined(Q_OS_WIN)
 Q_GUI_EXPORT bool qt_needs_a8_gamma_correction = false;
 
-static inline void grayBlendPixel(quint32 *dst, int coverage, int sr, int sg, int sb, const uint *gamma, const uchar *invgamma)
+static inline void grayBlendPixel(quint32 *dst, int coverage, QRgba64 slinear, const QColorProfile *colorProfile)
 {
     // Do a gammacorrected gray alphablend...
-    int dr = qRed(*dst);
-    int dg = qGreen(*dst);
-    int db = qBlue(*dst);
-
-    dr = gamma[dr];
-    dg = gamma[dg];
-    db = gamma[db];
-
-    int alpha = coverage;
-    int ialpha = 255 - alpha;
-    int nr = qt_div_255(sr * alpha + dr * ialpha);
-    int ng = qt_div_255(sg * alpha + dg * ialpha);
-    int nb = qt_div_255(sb * alpha + db * ialpha);
+    const QRgba64 dlinear = colorProfile->toLinear64(*dst);
 
-    nr = invgamma[nr];
-    ng = invgamma[ng];
-    nb = invgamma[nb];
+    QRgba64 blend = interpolate255(slinear, coverage, dlinear, 255 - coverage);
 
-    *dst = qRgb(nr, ng, nb);
+    *dst = colorProfile->fromLinear64(blend);
 }
-#endif
 
 static void qt_alphamapblit_uint32(QRasterBuffer *rasterBuffer,
                                    int x, int y, quint32 color,
@@ -5592,21 +5548,14 @@ static void qt_alphamapblit_uint32(QRasterBuffer *rasterBuffer,
     const quint32 c = color;
     const int destStride = rasterBuffer->bytesPerLine() / sizeof(quint32);
 
-#if defined(Q_OS_WIN)
-    const QDrawHelperGammaTables *tables = QGuiApplicationPrivate::instance()->gammaTables();
-    if (!tables)
+    const QColorProfile *colorProfile = QGuiApplicationPrivate::instance()->colorProfileForA8Text();
+    if (!colorProfile)
         return;
 
-    const uint *gamma = tables->qt_pow_gamma;
-    const uchar *invgamma = tables->qt_pow_invgamma;
-
-    int sr = gamma[qRed(color)];
-    int sg = gamma[qGreen(color)];
-    int sb = gamma[qBlue(color)];
+    const QRgba64 slinear = colorProfile->toLinear64(c);
 
     bool opaque_src = (qAlpha(color) == 255);
     bool doGrayBlendPixel = opaque_src && qt_needs_a8_gamma_correction;
-#endif
 
     if (!clip) {
         quint32 *dest = reinterpret_cast<quint32*>(rasterBuffer->scanLine(y)) + x;
@@ -5619,13 +5568,9 @@ static void qt_alphamapblit_uint32(QRasterBuffer *rasterBuffer,
                 } else if (coverage == 255) {
                     dest[i] = c;
                 } else {
-#if defined(Q_OS_WIN)
-                    if (QSysInfo::WindowsVersion >= QSysInfo::WV_XP && doGrayBlendPixel
-                        && qAlpha(dest[i]) == 255) {
-                        grayBlendPixel(dest+i, coverage, sr, sg, sb, gamma, invgamma);
-                    } else
-#endif
-                    {
+                    if (doGrayBlendPixel && qAlpha(dest[i]) == 255) {
+                        grayBlendPixel(dest+i, coverage, slinear, colorProfile);
+                    } else {
                         int ialpha = 255 - coverage;
                         dest[i] = INTERPOLATE_PIXEL_255(c, coverage, dest[i], ialpha);
                     }
@@ -5660,13 +5605,9 @@ static void qt_alphamapblit_uint32(QRasterBuffer *rasterBuffer,
                     } else if (coverage == 255) {
                         dest[xp] = c;
                     } else {
-#if defined(Q_OS_WIN)
-                        if (QSysInfo::WindowsVersion >= QSysInfo::WV_XP && doGrayBlendPixel
-                            && qAlpha(dest[xp]) == 255) {
-                            grayBlendPixel(dest+xp, coverage, sr, sg, sb, gamma, invgamma);
-                        } else
-#endif
-                        {
+                        if (doGrayBlendPixel && qAlpha(dest[xp]) == 255) {
+                            grayBlendPixel(dest+xp, coverage, slinear, colorProfile);
+                        } else {
                             int ialpha = 255 - coverage;
                             dest[xp] = INTERPOLATE_PIXEL_255(c, coverage, dest[xp], ialpha);
                         }
@@ -5700,6 +5641,11 @@ static void qt_alphamapblit_rgba8888(QRasterBuffer *rasterBuffer,
 }
 #endif
 
+inline static int qRgbAvg(QRgb rgb)
+{
+    return (qRed(rgb) * 5 + qGreen(rgb) * 6 + qBlue(rgb) * 5) / 16;
+}
+
 static void qt_alphargbblit_argb32(QRasterBuffer *rasterBuffer,
                                    int x, int y, const QRgba64 &color,
                                    const uint *src, int mapWidth, int mapHeight, int srcStride,
@@ -5707,21 +5653,13 @@ static void qt_alphargbblit_argb32(QRasterBuffer *rasterBuffer,
 {
     const quint32 c = color.toArgb32();
 
-    int sr = qRed(c);
-    int sg = qGreen(c);
-    int sb = qBlue(c);
     int sa = qAlpha(c);
 
-    const QDrawHelperGammaTables *tables = QGuiApplicationPrivate::instance()->gammaTables();
-    if (!tables)
+    const QColorProfile *colorProfile = QGuiApplicationPrivate::instance()->colorProfileForA32Text();
+    if (!colorProfile)
         return;
 
-    const uchar *gamma = tables->qt_pow_rgb_gamma;
-    const uchar *invgamma = tables->qt_pow_rgb_invgamma;
-
-    sr = gamma[sr];
-    sg = gamma[sg];
-    sb = gamma[sb];
+    const QRgba64 slinear = colorProfile->toLinear64(c);
 
     if (sa == 0)
         return;
@@ -5735,7 +5673,13 @@ static void qt_alphargbblit_argb32(QRasterBuffer *rasterBuffer,
                 if (coverage == 0xffffffff) {
                     dst[i] = c;
                 } else if (coverage != 0xff000000) {
-                    rgbBlendPixel(dst+i, coverage, sr, sg, sb, gamma, invgamma);
+                    if (dst[i] >= 0xff000000) {
+                        rgbBlendPixel(dst+i, coverage, slinear, colorProfile);
+                    } else {
+                        // Give up and do a naive blend.
+                        const int a = qRgbAvg(coverage);
+                        dst[i] = INTERPOLATE_PIXEL_255(c, a, dst[i], 255 - a);
+                    }
                 }
             }
 
@@ -5765,7 +5709,13 @@ static void qt_alphargbblit_argb32(QRasterBuffer *rasterBuffer,
                     if (coverage == 0xffffffff) {
                         dst[xp] = c;
                     } else if (coverage != 0xff000000) {
-                        rgbBlendPixel(dst+xp, coverage, sr, sg, sb, gamma, invgamma);
+                        if (dst[xp] >= 0xff000000) {
+                            rgbBlendPixel(dst+xp, coverage, slinear, colorProfile);
+                        } else {
+                            // Give up and do a naive blend.
+                            const int a = qRgbAvg(coverage);
+                            dst[xp] = INTERPOLATE_PIXEL_255(c, a, dst[xp], 255 - coverage);
+                        }
                     }
                 }
             } // for (i -> line.count)