Fixes the gif plugin's rendering for some animated gif files.

In the case of optimized animated gifs, we don't want to discard
the contents of the previous frame, this is handled if needed in the
disposal process.

Task-number: 247365
Reviewed-by: Samuel

12 files changed, 26 insertions, 4 deletions

diff --git a/src/plugins/imageformats/gif/qgifhandler.cpp b/src/plugins/imageformats/gif/qgifhandler.cpp
index de985d8..0f6a349 100644
--- a/src/plugins/imageformats/gif/qgifhandler.cpp
+++ b/src/plugins/imageformats/gif/qgifhandler.cpp
@@ -234,7 +234,7 @@ int QGIFFormat::decode(QImage *image, const uchar *buffer, int length,
 
 #define LM(l, m) (((m)<<8)|l)
     digress = false;
-    int initial = length;
+    const int initial = length;
     while (!digress && length) {
         length--;
         unsigned char ch=*buffer++;
@@ -333,7 +333,7 @@ int QGIFFormat::decode(QImage *image, const uchar *buffer, int length,
                     sheight = newtop + newheight;
 
                 QImage::Format format = trans_index >= 0 ? QImage::Format_ARGB32 : QImage::Format_RGB32;
-                if (image->isNull() || (image->size() != QSize(swidth, sheight)) || image->format() != format) {
+                if (image->isNull()) {
                     (*image) = QImage(swidth, sheight, format);
                     memset(image->bits(), 0, image->numBytes());
 
diff --git a/tests/auto/qimagereader/images/qt.gif b/tests/auto/qimagereader/images/qt.gif
new file mode 100644
index 0000000..e0a5a80
--- /dev/null
+++ b/tests/auto/qimagereader/images/qt.gif
diff --git a/tests/auto/qimagereader/images/qt1.gif b/tests/auto/qimagereader/images/qt1.gif
new file mode 100644
index 0000000..0ce910c
--- /dev/null
+++ b/tests/auto/qimagereader/images/qt1.gif
diff --git a/tests/auto/qimagereader/images/qt2.gif b/tests/auto/qimagereader/images/qt2.gif
new file mode 100644
index 0000000..993a315
--- /dev/null
+++ b/tests/auto/qimagereader/images/qt2.gif
diff --git a/tests/auto/qimagereader/images/qt3.gif b/tests/auto/qimagereader/images/qt3.gif
new file mode 100644
index 0000000..7391678
--- /dev/null
+++ b/tests/auto/qimagereader/images/qt3.gif
diff --git a/tests/auto/qimagereader/images/qt4.gif b/tests/auto/qimagereader/images/qt4.gif
new file mode 100644
index 0000000..41109a9
--- /dev/null
+++ b/tests/auto/qimagereader/images/qt4.gif
diff --git a/tests/auto/qimagereader/images/qt5.gif b/tests/auto/qimagereader/images/qt5.gif
new file mode 100644
index 0000000..5a3fb54
--- /dev/null
+++ b/tests/auto/qimagereader/images/qt5.gif
diff --git a/tests/auto/qimagereader/images/qt6.gif b/tests/auto/qimagereader/images/qt6.gif
new file mode 100644
index 0000000..f22e7c9
--- /dev/null
+++ b/tests/auto/qimagereader/images/qt6.gif
diff --git a/tests/auto/qimagereader/images/qt7.gif b/tests/auto/qimagereader/images/qt7.gif
new file mode 100644
index 0000000..a315671
--- /dev/null
+++ b/tests/auto/qimagereader/images/qt7.gif
diff --git a/tests/auto/qimagereader/images/qt8.gif b/tests/auto/qimagereader/images/qt8.gif
new file mode 100644
index 0000000..2a7d09e
--- /dev/null
+++ b/tests/auto/qimagereader/images/qt8.gif
diff --git a/tests/auto/qimagereader/qimagereader.qrc b/tests/auto/qimagereader/qimagereader.qrc
index 13ce582..e3113c6 100644
--- a/tests/auto/qimagereader/qimagereader.qrc
+++ b/tests/auto/qimagereader/qimagereader.qrc
@@ -1,5 +1,5 @@
-<!DOCTYPE RCC><RCC version="1.0">
-    <qresource>
+<RCC>
+    <qresource prefix="/" >
         <file>images/16bpp.bmp</file>
         <file>images/4bpp-rle.bmp</file>
         <file>images/YCbCr_cmyk.jpg</file>
@@ -47,5 +47,14 @@
         <file>images/tst7.png</file>
         <file>images/transparent.xpm</file>
         <file>images/trolltech.gif</file>
+        <file>images/qt.gif</file>
+        <file>images/qt1.gif</file>
+        <file>images/qt2.gif</file>
+        <file>images/qt3.gif</file>
+        <file>images/qt4.gif</file>
+        <file>images/qt5.gif</file>
+        <file>images/qt6.gif</file>
+        <file>images/qt7.gif</file>
+        <file>images/qt8.gif</file>
     </qresource>
 </RCC>
diff --git a/tests/auto/qimagereader/tst_qimagereader.cpp b/tests/auto/qimagereader/tst_qimagereader.cpp
index 18900b4..1403280 100644
--- a/tests/auto/qimagereader/tst_qimagereader.cpp
+++ b/tests/auto/qimagereader/tst_qimagereader.cpp
@@ -136,6 +136,7 @@ private slots:
 
 #if defined QTEST_HAVE_GIF
     void gifHandlerBugs();
+    void animatedGif();
 #endif
 
     void readCorruptImage_data();
@@ -671,6 +672,18 @@ void tst_QImageReader::gifHandlerBugs()
         QCOMPARE(im1.convertToFormat(QImage::Format_ARGB32), im2.convertToFormat(QImage::Format_ARGB32));
     }
 }
+
+void tst_QImageReader::animatedGif()
+{
+    QImageReader io(prefix + "qt.gif");
+    QImage image= io.read();
+    int i=0;
+    while(!image.isNull()){
+        QString frameName = QString(prefix + "qt%1.gif").arg(++i);
+        QCOMPARE(image, QImage(frameName));
+        image=io.read();
+    }
+}
 #endif
 
 class Server : public QObject