bugGNUstep - Bugs: bug #20304, PNG with alpha channel not...

Group
 
 

bug #20304: PNG with alpha channel not properly supported

Submitter:  Quentin Mathé <qmathe>
Submitted:  Sat 30 Jun 2007 10:21:15 PM UTC
   
 
Category:  Gui/AppKit Severity:  3 - Normal
Item Group:  Bug Status:  Works For Me
Privacy:  Public Assigned to:  FredKiefer
Open/Closed:  Declined
* Mandatory Fields

Add a New Comment Rich Markup
   

Mon 07 Jan 2008 01:02:27 PM UTC, comment #2: 

I tried to reproduce this problem with a current GNUstep installation and failed to. I tried with the art, cairo and xlib backend and all seemed to work more or less correctly. There is an interesting effect with the cario backend, as there some areas with high transparancy show in white. But this seems to be a different issue.

Fred Kiefer <FredKiefer>
Group Member
Sat 30 Jun 2007 10:37:42 PM UTC, comment #1: 

Failed to attach a screenshot in my initial post. So here is a link: <http://www.etoile-project.org/etoile/bugs/GNUstep_PNG_bug.png>

Quentin Mathé <qmathe>
Group Member
Sat 30 Jun 2007 10:21:15 PM UTC, original submission:  

With -make 2.0.0, -base 0.14, -gui 0.12 and -back 0.12 on Ubuntu Feisty Fawn.

According to my tests, PNG files with an alpha channel suffer from various drawing artifacts in GNUstep. In my tests, they are loaded through NSImage and drawn by method -compositeToPoint:operation:

The kind of drawing method which is used probably doesn't matter, the problem rather lies in PNG format reading code.

As an example, I attached a screenshot of a folder icon saved as PNG by GIMP and displayed by a GNUstep application.
Here is a link to original PNG file: <http://jesseross.com/clients/etoile/ui/icons/Folder-Folder.png>
If I save the folder icon file as TIFF and uses it instead of PNG one in the same application, the issue vanishes.

I initially thought the issue could be a result of additional embedded metadatas in the file (as Photoshop does it sometimes). But after having resaved the file in GIMP and tried many save options, I don't think this explanation is valid.

Drawing artifacts can be as extreme as seen in attached screenshot, but most of time they are visible only as jagged border or pixels drawn with incorrect color value.
The incorrectly drawn area of the folder icon is surely mapped to a partially transparent region of alpha channel.

Quentin.




Quentin Mathé <qmathe>
Group Member

 

(Note: upload size limit is set to 16384 kB, after insertion of the required escape characters.)

Attach Files:
   
   
Comment:
   

No files currently attached

 

Depends on the following items: None found

Items that depend on this one: None found

 

Carbon-Copy List
  • -email is unavailable- added by FredKiefer (Posted a comment)
  • -email is unavailable- added by qmathe (Submitted the item)
  •  

    There are 0 votes so far. Votes easily highlight which items people would like to see resolved in priority, independently of the priority of the item set by tracker managers.

    Only logged-in users can vote.

     

    Follow 3 latest changes.

    Date Changed by Updated Field Previous Value => Replaced by
    2008-01-07 FredKiefer StatusNone Works For Me
        Assigned toNone FredKiefer
        Open/ClosedOpen Declined

    Back to the top

    Powered by Savane 3.13-02a9.
    Corresponding source code