250786 - [Xlib] scaled images render as garbage

Status: RESOLVED FIXED

(Core Graveyard :: GFX: Xlib, defect)

Description

[Christian :Biesinger (don't email me, ping me on IRC)]

see, for example, the bookmark folder icon in the classic theme - it's 22x16,
downscaled to 16x16 (I think).

Comment 1

[R.K.Aa.]

related to bug 250635?

Comment 2

[Christian :Biesinger (don't email me, ping me on IRC)]

hm... this specific image does not use -moz-image-region. also, this is limited
to the xlib toolkit.

Comment 3

[Christian :Biesinger (don't email me, ping me on IRC)]

this regressed between 2003-11-23 02:00 and 2003-11-23 14:00 (PDT)

list of checkins:
http://bonsai.mozilla.org/cvsquery.cgi?treeid=default&module=all&branch=HEAD&branchtype=match&dir=&file=&filetype=match&who=&whotype=match&sortby=Date&hours=2&date=explicit&mindate=2003-11-23+12%3A00+CEST&maxdate=2003-11-24+00%3A00+CEST&cvsroot=%2Fcvsroot

this indicates Bug 150881

Comment 4

[Christian :Biesinger (don't email me, ping me on IRC)]

in fact, this seems to affect also pngs with alpha channels as well as images
without any transparency

Comment 5

[Christian :Biesinger (don't email me, ping me on IRC)]

Attachment: patch

Comment 6

[Christian :Biesinger (don't email me, ping me on IRC)]

So, the problem was: aDX/aDY are coordinates pointing somewhere into the
rendering context. So they are just used to position the scaled image. Trying to
put the scaled image into the buffer at aDX/aDY position probably wrote to
random memory, although I didn't verify that; possibly RectStretch just did nothing.

So the fix is: Scale the image into position (0, 0) in the allocated buffer, and
draw that result at (aDX, aDY).

Comment 7

[Christian :Biesinger (don't email me, ping me on IRC)]

Comment on attachment 153577 [details] [diff] [review]
patch

this doesn't fix pngs with an alpha channel

Comment 8

[Christian :Biesinger (don't email me, ping me on IRC)]

Attachment: patch v2

testcase for scaling PNGs with alpha:
data:text/html,<img src="http://www.w3.org/Graphics/PNG/alphatest.png"
width="300">

Comment 9

[Roland Mainz]

Comment on attachment 153578 [details] [diff] [review]
patch v2

r=[e-mail]

Comment 10

[Christian :Biesinger (don't email me, ping me on IRC)]

Checking in gfx/src/xlib/nsImageXlib.cpp;
/cvsroot/mozilla/gfx/src/xlib/nsImageXlib.cpp,v  <--  nsImageXlib.cpp
new revision: 1.47; previous revision: 1.46
done