[Chicken-janitors] #1271: Imlib2 image-create initializes w/ garbage

[Chicken Trac]

#1271: Imlib2 image-create initializes w/ garbage
------------------------+---------------------
 Reporter:  sandra      |      Owner:
     Type:  defect      |     Status:  new
 Priority:  major       |  Milestone:  someday
Component:  extensions  |    Version:  4.10.x
 Keywords:  imlib2      |
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 image-create calls the foreign lambda imlib_create_image which initializes
 as garbage.
 To fix that, it then calls (image-fill-rectangle img (color/rgba 0 0 0 0)
 0 0 width height) with the purpose of setting it all as 0 0 0 0 pixels.
 The problem is that doesn't work, it stays garbage, because image-fill-
 rectangle doesn't overwrite pixels, it just blends with them.

 As a proof of concept for this bug,
 try calling (image-fill-rectangle output (color/rgba 0 0 0 0) 0 0 w h) on
 an image after calling (image-fill-rectangle output (color/rgba 255 255
 255 255) 0 0 w h). It'll still be white, because filling a rectangle with
 transparency doesn't overwrite with transparency, it just adds
 transparency "on top".

 What a weird bug; I couldn't come up with a solution. Love the imlib2 egg,
 but this makes create-image sort of a useless part of it. There's no
 documented way to clear or erase pixels, to set them to transparent, by
 using the egg.

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Ticket URL: <http://bugs.call-cc.org/ticket/1271>
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