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

 
 

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bug #20304: PNG with alpha channel not properly supported

Submitted by:  Quentin Mathé <qmathe>
Submitted on:  Sat 30 Jun 2007 10:21:15 PM UTC  
 
Category: Gui/AppKitSeverity: 3 - Normal
Item Group: BugStatus: Works For Me
Privacy: PublicAssigned to: Fred Kiefer <FredKiefer>
Open/Closed: Declined

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>
Project MemberIn charge of this item.
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>
Project 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>
Project Member

 

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  • -unavailable- added by FredKiefer (Posted a comment)
  • -unavailable- added by qmathe (Submitted the item)
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    Follow 3 latest changes.

    Date Changed By Updated Field Previous Value => Replaced By
    Mon 07 Jan 2008 01:02:27 PM UTCFredKieferStatusNone=>Works For Me
      Assigned toNone=>FredKiefer
      Open/ClosedOpen=>Declined

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