Fix a regression when painting CMYK over ARGB32_Premultiplied

With the introduction of CMYK32 the old logic of assuming depth
meant compatible alpha version no longer works. So change the logic
to more explicitly return compatible opaque or alpha versions and
remove the now invalid qt_maybeAlphaVersionWithSameDepth.

Change-Id: Ib1f7b76b0ce0eae7d49a0dfe369918a746bbe2b4
Reviewed-by: Giuseppe D'Angelo <giuseppe.dangelo@kdab.com>

5 files changed, 116 insertions, 15 deletions

diff --git a/src/gui/image/qimage_p.h b/src/gui/image/qimage_p.h
index ca7a4de4d8..7dbddbc67d 100644
--- a/src/gui/image/qimage_p.h
+++ b/src/gui/image/qimage_p.h
@@ -322,6 +322,63 @@ inline QImage::Format qt_alphaVersion(QImage::Format format)
     return QImage::Format_ARGB32_Premultiplied;
 }
 
+// Returns an opaque version that is compatible with format
+inline QImage::Format qt_maybeDataCompatibleOpaqueVersion(QImage::Format format)
+{
+    switch (format) {
+    case QImage::Format_ARGB6666_Premultiplied:
+        return QImage::Format_RGB666;
+    case QImage::Format_ARGB4444_Premultiplied:
+        return QImage::Format_RGB444;
+    case QImage::Format_RGBA8888:
+    case QImage::Format_RGBA8888_Premultiplied:
+        return QImage::Format_RGBX8888;
+    case QImage::Format_A2BGR30_Premultiplied:
+        return QImage::Format_BGR30;
+    case QImage::Format_A2RGB30_Premultiplied:
+        return QImage::Format_RGB30;
+    case QImage::Format_RGBA64:
+    case QImage::Format_RGBA64_Premultiplied:
+        return QImage::Format_RGBX64;
+    case QImage::Format_RGBA16FPx4:
+    case QImage::Format_RGBA16FPx4_Premultiplied:
+        return QImage::Format_RGBX16FPx4;
+    case QImage::Format_RGBA32FPx4:
+    case QImage::Format_RGBA32FPx4_Premultiplied:
+        return QImage::Format_RGBX32FPx4;
+    case QImage::Format_ARGB32_Premultiplied:
+    case QImage::Format_ARGB32:
+        return QImage::Format_RGB32;
+    case QImage::Format_RGB16:
+    case QImage::Format_RGB32:
+    case QImage::Format_RGB444:
+    case QImage::Format_RGB555:
+    case QImage::Format_RGB666:
+    case QImage::Format_RGB888:
+    case QImage::Format_BGR888:
+    case QImage::Format_RGBX8888:
+    case QImage::Format_BGR30:
+    case QImage::Format_RGB30:
+    case QImage::Format_RGBX64:
+    case QImage::Format_RGBX16FPx4:
+    case QImage::Format_RGBX32FPx4:
+    case QImage::Format_Grayscale8:
+    case QImage::Format_Grayscale16:
+    case QImage::Format_CMYK32:
+        return format; // Already opaque
+    case QImage::Format_Mono:
+    case QImage::Format_MonoLSB:
+    case QImage::Format_Indexed8:
+    case QImage::Format_ARGB8565_Premultiplied:
+    case QImage::Format_ARGB8555_Premultiplied:
+    case QImage::Format_Alpha8:
+    case QImage::Format_Invalid:
+    case QImage::NImageFormats:
+        break;
+    }
+    return format; // No compatible opaque versions
+}
+
 constexpr QImage::Format qt_toUnpremultipliedFormat(QImage::Format format)
 {
     // Assumes input is already a premultiplied format with an unpremultiplied counterpart
@@ -380,10 +437,60 @@ inline bool qt_fpColorPrecision(QImage::Format format)
     return false;
 }
 
-inline QImage::Format qt_maybeAlphaVersionWithSameDepth(QImage::Format format)
+inline QImage::Format qt_maybeDataCompatibleAlphaVersion(QImage::Format format)
 {
-    const QImage::Format toFormat = qt_alphaVersion(format);
-    return qt_depthForFormat(format) == qt_depthForFormat(toFormat) ? toFormat : format;
+    switch (format) {
+    case QImage::Format_RGB32:
+        return QImage::Format_ARGB32_Premultiplied;
+    case QImage::Format_RGB666:
+        return QImage::Format_ARGB6666_Premultiplied;
+    case QImage::Format_RGB444:
+        return QImage::Format_ARGB4444_Premultiplied;
+    case QImage::Format_RGBX8888:
+        return QImage::Format_RGBA8888_Premultiplied;
+    case QImage::Format_BGR30:
+        return QImage::Format_A2BGR30_Premultiplied;
+    case QImage::Format_RGB30:
+        return QImage::Format_A2RGB30_Premultiplied;
+    case QImage::Format_RGBX64:
+        return QImage::Format_RGBA64_Premultiplied;
+    case QImage::Format_RGBX16FPx4:
+        return QImage::Format_RGBA16FPx4_Premultiplied;
+    case QImage::Format_RGBX32FPx4:
+        return QImage::Format_RGBA32FPx4_Premultiplied;
+    case QImage::Format_ARGB32:
+    case QImage::Format_ARGB32_Premultiplied:
+    case QImage::Format_ARGB8565_Premultiplied:
+    case QImage::Format_ARGB8555_Premultiplied:
+    case QImage::Format_ARGB6666_Premultiplied:
+    case QImage::Format_ARGB4444_Premultiplied:
+    case QImage::Format_RGBA8888:
+    case QImage::Format_RGBA8888_Premultiplied:
+    case QImage::Format_A2BGR30_Premultiplied:
+    case QImage::Format_A2RGB30_Premultiplied:
+    case QImage::Format_Alpha8:
+    case QImage::Format_RGBA64:
+    case QImage::Format_RGBA64_Premultiplied:
+    case QImage::Format_RGBA16FPx4:
+    case QImage::Format_RGBA16FPx4_Premultiplied:
+    case QImage::Format_RGBA32FPx4:
+    case QImage::Format_RGBA32FPx4_Premultiplied:
+        return format; // Already alpha versions
+    case QImage::Format_Mono:
+    case QImage::Format_MonoLSB:
+    case QImage::Format_Indexed8:
+    case QImage::Format_RGB16:
+    case QImage::Format_RGB555:
+    case QImage::Format_RGB888:
+    case QImage::Format_BGR888:
+    case QImage::Format_Grayscale8:
+    case QImage::Format_Grayscale16:
+    case QImage::Format_CMYK32:
+    case QImage::Format_Invalid:
+    case QImage::NImageFormats:
+        break;
+    }
+    return format; // No data-compatible alpha version
 }
 
 inline QImage::Format qt_opaqueVersionForPainting(QImage::Format format)
diff --git a/src/gui/painting/qpaintengine_raster.cpp b/src/gui/painting/qpaintengine_raster.cpp
index cea7024aaa..f62373d4ef 100644
--- a/src/gui/painting/qpaintengine_raster.cpp
+++ b/src/gui/painting/qpaintengine_raster.cpp
@@ -3713,15 +3713,9 @@ bool QRasterPaintEnginePrivate::canUseImageBlitting(QPainter::CompositionMode mo
 
     QImage::Format dFormat = rasterBuffer->format;
     QImage::Format sFormat = image.format();
-    // Formats must match or source format must be a subset of destination format
-    if (dFormat != sFormat && image.pixelFormat().alphaUsage() == QPixelFormat::IgnoresAlpha) {
-        if ((sFormat == QImage::Format_RGB32 && dFormat == QImage::Format_ARGB32)
-            || (sFormat == QImage::Format_RGBX8888 && dFormat == QImage::Format_RGBA8888)
-            || (sFormat == QImage::Format_RGBX64 && dFormat == QImage::Format_RGBA64))
-            sFormat = dFormat;
-        else
-            sFormat = qt_maybeAlphaVersionWithSameDepth(sFormat); // this returns premul formats
-    }
+    // Formats must match or source format must be an opaque version of destination format
+    if (dFormat != sFormat && image.pixelFormat().alphaUsage() == QPixelFormat::IgnoresAlpha)
+        dFormat = qt_maybeDataCompatibleOpaqueVersion(dFormat);
     return (dFormat == sFormat);
 }
 
diff --git a/src/gui/painting/qrhibackingstore.cpp b/src/gui/painting/qrhibackingstore.cpp
index 72ab28f1fc..586dfb44a4 100644
--- a/src/gui/painting/qrhibackingstore.cpp
+++ b/src/gui/painting/qrhibackingstore.cpp
@@ -60,7 +60,7 @@ QImage::Format QRhiBackingStore::format() const
     // image must have an alpha channel. Hence upgrading the format. Matches
     // what other platforms (Windows, xcb) do.
     if (QImage::toPixelFormat(fmt).alphaUsage() != QPixelFormat::UsesAlpha)
-        fmt = qt_maybeAlphaVersionWithSameDepth(fmt);
+        fmt = qt_maybeDataCompatibleAlphaVersion(fmt);
 
     return fmt;
 }
diff --git a/src/plugins/platforms/windows/qwindowsbackingstore.cpp b/src/plugins/platforms/windows/qwindowsbackingstore.cpp
index 0f9d0172d9..07918f6094 100644
--- a/src/plugins/platforms/windows/qwindowsbackingstore.cpp
+++ b/src/plugins/platforms/windows/qwindowsbackingstore.cpp
@@ -117,7 +117,7 @@ void QWindowsBackingStore::resize(const QSize &size, const QRegion &region)
         if (QImage::toPixelFormat(format).alphaUsage() == QPixelFormat::UsesAlpha)
             m_alphaNeedsFill = true;
         else // upgrade but here we know app painting does not rely on alpha hence no need to fill
-            format = qt_maybeAlphaVersionWithSameDepth(format);
+            format = qt_maybeDataCompatibleAlphaVersion(format);
 
         QWindowsNativeImage *oldwni = m_image.data();
         auto *newwni = new QWindowsNativeImage(size.width(), size.height(), format);
diff --git a/src/plugins/platforms/xcb/qxcbbackingstore.cpp b/src/plugins/platforms/xcb/qxcbbackingstore.cpp
index 0659cf9fc4..8353fac6a9 100644
--- a/src/plugins/platforms/xcb/qxcbbackingstore.cpp
+++ b/src/plugins/platforms/xcb/qxcbbackingstore.cpp
@@ -173,7 +173,7 @@ void QXcbBackingStoreImage::init(const QSize &size, uint depth, QImage::Format f
     m_qimage_format = format;
     m_hasAlpha = QImage::toPixelFormat(m_qimage_format).alphaUsage() == QPixelFormat::UsesAlpha;
     if (!m_hasAlpha)
-        m_qimage_format = qt_maybeAlphaVersionWithSameDepth(m_qimage_format);
+        m_qimage_format = qt_maybeDataCompatibleAlphaVersion(m_qimage_format);
 
     memset(&m_shm_info, 0, sizeof m_shm_info);