Fix transparency in 16 bit and 24 bit ico files

As a result of the fix for QTBUG-75214, Qt inadvertently no longer
reads the AND mask that specifies transparency for 16-bit and 24-bit
ico files. This is because it tries to detect 32-bit icons by checking
icoAttrib.depth == 32, but icoAttrib.depth is set to the depth of the
QImage, not the depth of the icon, and 32-bit QImage is used for all of
the non-indexed cases (16-bit, 24-bit and 32-bit.)

This commit instead uses icoAttrib.nbits, which should reliably
determine whether or not the icon is 32-bit. This makes the behavior
consistent with other ico reading software, including Windows.

Also, adds a unit test that verifies correct behavior of icon masks,
checking for both QTBUG-75214 and QTBUG-113319.

Amends 1d128ed1dfbcf49453ada922e54381c37264fde5.

Fixes: QTBUG-113319
Change-Id: I89ac86ff16054c8925fff6afc8c530fa737f8385
Pick-to: 6.6 6.5 6.2 5.15
Reviewed-by: Eirik Aavitsland <eirik.aavitsland@qt.io>

1 files changed, 1 insertions, 1 deletions

diff --git a/src/plugins/imageformats/ico/qicohandler.cpp b/src/plugins/imageformats/ico/qicohandler.cpp
index 3bcf30bfc6..e58dde4e97 100644
--- a/src/plugins/imageformats/ico/qicohandler.cpp
+++ b/src/plugins/imageformats/ico/qicohandler.cpp
@@ -499,7 +499,7 @@ QImage ICOReader::iconAt(int index)
                     if (!image.isNull()) {
                         readBMP(image);
                         if (!image.isNull()) {
-                            if (icoAttrib.depth == 32) {
+                            if (icoAttrib.nbits == 32) {
                                 img = std::move(image).convertToFormat(QImage::Format_ARGB32_Premultiplied);
                             } else {
                                 QImage mask(image.width(), image.height(), QImage::Format_Mono);