https://bugs.documentfoundation.org/show_bug.cgi?id=173903
Bug ID: 173903
Summary: Clipping rectangle size discrepancy in CairoSDPR
Product: LibreOffice
Version: 25.2.0.0 alpha0+
Hardware: All
OS: Linux (All)
Status: UNCONFIRMED
Severity: normal
Priority: medium
Component: graphics stack
Assignee: [email protected]
Reporter: [email protected]
This is a follow-up bug from bug 168910. Please see that bug for reproduction
instructions.
When using CairoSDPR, scrolling past images anchored *as character* in Writer
causes many white lines to be drawn across the image. From bug 168910 comment
27:
> The root cause is CairoPixelProcessor2D "losing" the bottom and right rows
> of pixels when applying clipping rectangles (via MaskPrimitive2D). When we
> have Writer images anchored *as character* which extend past the window,
> CairoSDPR fails to draw the bottom and right rows of pixels. They're
> rendered as white lines, instead. This is quietly happening in a few other
> places, too, but it's most visible in the anchored image case reported here.
>
> The commit referenced by comment 2 didn't cause this bug. It made the
> problem more visible by reenabling an optimization that tries to reuse
> previously-rendered image data while scrolling. That part of the code is
> working fine; the problem is that the data it's trying to reuse is
> incomplete.
While this problem is most visible in images, it is a more general problem and
may appear in other parts of the UI (such as the space between pages).
CairoSDPR should be updated to handle this type of clipping better. It's
possible that this can be fixed with a math tweak, but it may also be necessary
to implement support for some more typical sort of screen space AABB/scissor
rect for these cases, rather than using logical device space polygons.
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