[cairo-bugs] [Bug 16469] New: Device offset is not affected by scaling

bugzilla-daemon at freedesktop.org bugzilla-daemon at freedesktop.org
Sun Jun 22 18:55:09 PDT 2008


           Summary: Device offset is not affected by scaling
           Product: cairo
           Version: 1.6.5
          Platform: Other
        OS/Version: All
            Status: NEW
          Severity: normal
          Priority: medium
         Component: general
        AssignedTo: cworth at cworth.org
        ReportedBy: ventnor.bugzilla at yahoo.com.au
         QAContact: cairo-bugs at cairographics.org

While implementing a new CSS feature in Mozilla Gecko I stumbled across a bug
regarding device offsets and scaling that make the feature quite glitchy.

Device offsets seem to be unaffected by scaling when painted onto a surface
with scaling applied.

e.g. - surface A is scaled by 0.5, 0.5
- surface B has a device offset of -40, -40.
- draw a rectangle on surface A at X=40, Y=40, width=20, height=20. This means
the actual size is 20, 20, 10, 10 due to scaling.
- draw a rectangle of exactly the same coordinates on surface B.
- mask or paint surface B onto surface A.

The result is that the rectangle on surface B is painted at half-size, but it
is drawn at 40, 40, so the device offsets didn't allow the X or Y of B's
rectangle to be scaled like A's.

Hopefully this can be fixed soon as this blocks a proper implementation of
text-shadow and box-shadow in Gecko.

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