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Paint problems when using transparency [message #41462]

Thu, 19 December 2013 23:57

Didier
Messages: 725
Registered: November 2008
Location: France

Contributor

Hi all,

I have a problem that is driving me nuts Dead

I am trying to make my GraphCtrl package as fast as possible and to do so I am trying to take advantage of the fast drawing of images when directly draw with native Draw instance passed to Ctrls.

The speed difference is very high (80 times faster) and everything works fine until:

transparency comes in
SUBPIXEL is used

So I made a test case hoping that someone could help me.
The test case basically does the following for each Ctrl

create a BufferPainter
fill the buffer painter with transparent background (in case you want to see behind the Ctrl)
Paint a white rectagle on upper half of the Ctrl
Paint an image containg green circle : half opaque, and half transparent (partially transparent)
draw a red line accross the Ctrl
draw the resulting image on the Ctrl area

There are 4 different flavors (testCtrl_1,2,3,4) and 4 different Painter modes used (antialiased, ...)
The defaults encountered are the following:

Transparent green becomes violet when overlapping the white rectangle
red line is not drawn properly when overlapping transparent area AND in SUBPIXEL mode

I know that a Premultiply() will probably correct the violet issue, but I can't find where to put it.
For the other problem ... I have no Idea what is going wrong

The result is in the following image
index.php?t=getfile&id=4376&private=0

The code of the test case is joined

Hopping to get some help

Attachment: painting_bug.png
(Size: 51.01KB, Downloaded 830 times)
Attachment: Test_painting.zip
(Size: 4.14KB, Downloaded 560 times)

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