Fix accuracy of ARGB32->A2RGB30 conversions

It was converted over ARGB32PM, when it should have been directly
converted to not lose accuracy, instead there was an unnecessary direct
ARGB32->RGB30 conversion, which was converted to the necessary type.

This also improves the selection of conversion over ARGB32PM or RGBA64PM
for ARGB32 and RGBA8888 by using 32-bit conversion when alpha is not
relevant.

Change-Id: I5990d8a23b2909d3910d8c1213fa46477742b052
Reviewed-by: Eirik Aavitsland <eirik.aavitsland@qt.io>

1 files changed, 23 insertions, 0 deletions

diff --git a/src/gui/image/qimage_p.h b/src/gui/image/qimage_p.h
index 9e2d9c86bb..0930955f5a 100644
--- a/src/gui/image/qimage_p.h
+++ b/src/gui/image/qimage_p.h
@@ -276,6 +276,29 @@ inline QImage::Format qt_alphaVersion(QImage::Format format)
     return QImage::Format_ARGB32_Premultiplied;
 }
 
+inline bool qt_highColorPrecision(QImage::Format format, bool opaque = false)
+{
+    // Formats with higher color precision than ARGB32_Premultiplied.
+    switch (format) {
+    case QImage::Format_ARGB32:
+    case QImage::Format_RGBA8888:
+        return !opaque;
+    case QImage::Format_BGR30:
+    case QImage::Format_RGB30:
+    case QImage::Format_A2BGR30_Premultiplied:
+    case QImage::Format_A2RGB30_Premultiplied:
+    case QImage::Format_RGBX64:
+    case QImage::Format_RGBA64:
+    case QImage::Format_RGBA64_Premultiplied:
+    case QImage::Format_Grayscale16:
+        return true;
+    default:
+        break;
+    }
+    return false;
+}
+
+
 inline QImage::Format qt_maybeAlphaVersionWithSameDepth(QImage::Format format)
 {
     const QImage::Format toFormat = qt_alphaVersion(format);