Use backing store formats with alpha

We depend on being able to punch holes in the backing store when
integrating with FBO elements. To do that we need a format with an alpha
channel. This was only working previously because RGB32 didn't mask when
filling or when converting to ARGB32_PM, but other formats didn't.

Also unifies the logic for getting alpha versions of QImage formats.

Task-number: QTBUG-50281
Change-Id: Ied1325f60e2b67d9ea2dfa9701b06fc2231ebfca
Reviewed-by: Laszlo Agocs <[email protected]>

4 files changed, 42 insertions, 51 deletions

diff --git a/src/gui/image/qimage.cpp b/src/gui/image/qimage.cpp
index a992ad6feab..6ec1eecfb14 100644
--- a/src/gui/image/qimage.cpp
+++ b/src/gui/image/qimage.cpp
@@ -4623,32 +4623,7 @@ QImage QImage::transformed(const QTransform &matrix, Qt::TransformationMode mode
 
     if (complex_xform || mode == Qt::SmoothTransformation) {
         if (d->format < QImage::Format_RGB32 || !hasAlphaChannel()) {
-            switch(d->format) {
-            case QImage::Format_RGB16:
-                target_format = Format_ARGB8565_Premultiplied;
-                break;
-            case QImage::Format_RGB555:
-                target_format = Format_ARGB8555_Premultiplied;
-                break;
-            case QImage::Format_RGB666:
-                target_format = Format_ARGB6666_Premultiplied;
-                break;
-            case QImage::Format_RGB444:
-                target_format = Format_ARGB4444_Premultiplied;
-                break;
-            case QImage::Format_RGBX8888:
-                target_format = Format_RGBA8888_Premultiplied;
-                break;
-            case QImage::Format_BGR30:
-                target_format = Format_A2BGR30_Premultiplied;
-                break;
-            case QImage::Format_RGB30:
-                target_format = Format_A2RGB30_Premultiplied;
-                break;
-            default:
-                target_format = Format_ARGB32_Premultiplied;
-                break;
-            }
+            target_format = qt_alphaVersion(d->format);
         }
     }
 
diff --git a/src/gui/image/qimage_p.h b/src/gui/image/qimage_p.h
index 3badda08642..f9ad6c0ac0d 100644
--- a/src/gui/image/qimage_p.h
+++ b/src/gui/image/qimage_p.h
@@ -161,10 +161,45 @@ inline int qt_depthForFormat(QImage::Format format)
     }
     return depth;
 }
+
 #if defined(_M_ARM)
 #pragma optimize("", on)
 #endif
 
+inline QImage::Format qt_alphaVersion(QImage::Format format)
+{
+    switch (format) {
+    case QImage::Format_RGB16:
+        return QImage::Format_ARGB8565_Premultiplied;
+    case QImage::Format_RGB555:
+        return QImage::Format_ARGB8555_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;
+    default:
+        break;
+    }
+    return QImage::Format_ARGB32_Premultiplied;
+}
+
+inline QImage::Format qt_alphaVersionForPainting(QImage::Format format)
+{
+    QImage::Format toFormat = qt_alphaVersion(format);
+#if defined(__ARM_NEON__) || defined(__SSE2__)
+    // If we are switching depth anyway and we have optimized ARGB32PM routines, upgrade to that.
+    if (qt_depthForFormat(format) != qt_depthForFormat(toFormat))
+        toFormat = QImage::Format_ARGB32_Premultiplied;
+#endif
+    return toFormat;
+}
+
 QT_END_NAMESPACE
 
 #endif // QIMAGE_P_H
diff --git a/src/gui/image/qpixmap_raster.cpp b/src/gui/image/qpixmap_raster.cpp
index a2b84b358e2..bbdf77355e1 100644
--- a/src/gui/image/qpixmap_raster.cpp
+++ b/src/gui/image/qpixmap_raster.cpp
@@ -178,20 +178,7 @@ void QRasterPlatformPixmap::fill(const QColor &color)
         int alpha = color.alpha();
         if (alpha != 255) {
             if (!image.hasAlphaChannel()) {
-                QImage::Format toFormat;
-#if !(defined(__ARM_NEON__) || defined(__SSE2__))
-                if (image.format() == QImage::Format_RGB16)
-                    toFormat = QImage::Format_ARGB8565_Premultiplied;
-                else if (image.format() == QImage::Format_RGB666)
-                    toFormat = QImage::Format_ARGB6666_Premultiplied;
-                else if (image.format() == QImage::Format_RGB555)
-                    toFormat = QImage::Format_ARGB8555_Premultiplied;
-                else if (image.format() == QImage::Format_RGB444)
-                    toFormat = QImage::Format_ARGB4444_Premultiplied;
-                else
-#endif
-                    toFormat = QImage::Format_ARGB32_Premultiplied;
-
+                QImage::Format toFormat = qt_alphaVersionForPainting(image.format());
                 if (!image.isNull() && qt_depthForFormat(image.format()) == qt_depthForFormat(toFormat)) {
                     image.detach();
                     image.d->format = toFormat;
@@ -314,17 +301,7 @@ void QRasterPlatformPixmap::createPixmapForImage(QImage &sourceImage, Qt::ImageC
                     : QImage::Format_RGB32;
         } else {
             QImage::Format opaqueFormat = QNativeImage::systemFormat();
-            QImage::Format alphaFormat = QImage::Format_ARGB32_Premultiplied;
-
-#if !defined(__ARM_NEON__) && !defined(__SSE2__)
-            switch (opaqueFormat) {
-            case QImage::Format_RGB16:
-                alphaFormat = QImage::Format_ARGB8565_Premultiplied;
-                break;
-            default: // We don't care about the others...
-                break;
-            }
-#endif
+            QImage::Format alphaFormat = qt_alphaVersionForPainting(opaqueFormat);
 
             if (!sourceImage.hasAlphaChannel()) {
                 format = opaqueFormat;
diff --git a/src/plugins/platforms/xcb/qxcbbackingstore.cpp b/src/plugins/platforms/xcb/qxcbbackingstore.cpp
index 1825a463d07..006df320feb 100644
--- a/src/plugins/platforms/xcb/qxcbbackingstore.cpp
+++ b/src/plugins/platforms/xcb/qxcbbackingstore.cpp
@@ -51,6 +51,7 @@
 #include <qscreen.h>
 #include <QtGui/private/qhighdpiscaling_p.h>
 #include <qpa/qplatformgraphicsbuffer.h>
+#include <private/qimage_p.h>
 
 #include <algorithm>
 QT_BEGIN_NAMESPACE
@@ -172,6 +173,9 @@ QXcbShmImage::QXcbShmImage(QXcbScreen *screen, const QSize &size, uint depth, QI
             qWarning() << "QXcbBackingStore: Error while marking the shared memory segment to be destroyed";
     }
 
+    if (QImage::toPixelFormat(format).alphaUsage() == QPixelFormat::IgnoresAlpha)
+        format = qt_alphaVersionForPainting(format);
+
     m_qimage = QImage( (uchar*) m_xcb_image->data, m_xcb_image->width, m_xcb_image->height, m_xcb_image->stride, format);
     m_graphics_buffer = new QXcbShmGraphicsBuffer(&m_qimage);
 }