Fix IsTransparent() for unloaded graphics

Fix Graphic::IsAlpha() and Graphic::IsTransparent() for unloaded
graphics. This fixes tdf#118036.

GraphicDescriptor::Detect(true) is currently used to read the image size
from the header of images which are not being fully loaded yet.  This
change extends GraphicDescriptor to also report whether the image
supports transparency or alpha, implemented only for PNG format so far.

Change-Id: I1753c0d11491f1dc518e23da8d7b3842945770cb
Reviewed-on: https://gerrit.libreoffice.org/81785
Tested-by: Jenkins
Reviewed-by: Miklos Vajna <vmiklos@collabora.com>

1 files changed, 8 insertions, 0 deletions

diff --git a/include/vcl/graphicfilter.hxx b/include/vcl/graphicfilter.hxx
index eea2e9ac8b7d..45fe8e261f9e 100644
--- a/include/vcl/graphicfilter.hxx
+++ b/include/vcl/graphicfilter.hxx
@@ -145,6 +145,8 @@ class VCL_DLLPUBLIC GraphicDescriptor final
     GraphicFileFormat   nFormat;
     bool const          bOwnStream;
     sal_uInt8 mnNumberOfImageComponents;
+    bool                bIsTransparent;
+    bool                bIsAlpha;
 
     void                ImpConstruct();
 
@@ -214,6 +216,12 @@ public:
     /** @return number of color channels */
     sal_uInt8 GetNumberOfImageComponents() const { return mnNumberOfImageComponents; }
 
+    /** @return whether image supports transparency */
+    bool IsTransparent() const { return bIsTransparent; }
+
+    /** @return whether image supports alpha values for translucent colours */
+    bool IsAlpha() const { return bIsAlpha; }
+
     /** @return filter number that is needed by the GraphFilter to read this format */
     static OUString GetImportFormatShortName( GraphicFileFormat nFormat );
 };