[haiku-bugs] Re: [Haiku] #2946: BGradient does not support alpha transparency
- From: "pulkomandy" <trac@xxxxxxxxxxxx>
- Date: Thu, 24 Jul 2014 09:41:13 -0000
#2946: BGradient does not support alpha transparency
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Reporter: sdeken | Owner: stippi
Type: bug | Status: new
Priority: normal | Milestone: R1
Component: Kits/Interface Kit | Version: R1/pre-alpha1
Resolution: | Keywords:
Blocked By: | Blocking:
Has a Patch: 0 | Platform: All
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Comment (by pulkomandy):
Ok, after some investigation, here is what I found:
* The gradient generator (agg_span_gradient.h) generates the right alpha
and color values, so up to there things are ok.
* However, it generates a single span for each horizontal line. It seems
something down the rendering pipeline doesn't expect the alpha value to
change for pixels in a span, so the whole span is blended using the alpha
value of the first pixel.
This can be shown using the gradients test:
* Scroll the view to the right
* Using the scrollbar arrow, scroll it back to the left one pixel at a
time
The gradients drawing will be done one column at a time, and it will look
good. If you scroll a bit faster (for example using the scrollbar knob),
you can see the vertical bands using the same alpha value for each redraw
rectangle.
I wanted to try using the unpacked scanline rasterizer using ClipToPicture
but things went even worse. Will open a separate report for that.
--
Ticket URL: <https://dev.haiku-os.org/ticket/2946#comment:4>
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