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Transparent GIFs and GapiSurfaces - is it a problem?


Transparent GIFs and GapiSurfaces - is it a problem?

Postby ZOOM » Jun 25, 2002 @ 3:51pm

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Postby DillRye » Jun 27, 2002 @ 6:24pm

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Postby ZOOM » Jun 28, 2002 @ 10:10am

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Postby Johan » Jun 28, 2002 @ 10:44am

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Postby Johan » Jun 29, 2002 @ 9:50pm

Hmm. Basically it wasn't as easy as I thought. The GIF decoder built into all Pocket PCs (IMGDECMP.DLL) does not in itself decode GIFs correctly.

The way IMGDECMP works now is so that all transparent parts of a GIF image are rendered with a white color (regardless if you ask it to specifically use another color). When Pocket Internet Explorer draws a transparent GIF it simply replaces all these white pixels in the transparent GIF (including the mask background which has become white during the rendering process) with the background image.

This has the effect that if you have white pixels in your GIF image they will simply be replaced by the background. I have attached a picture below illustrating how this looks like in Internet Explorer:

Image

So, the solution to your problem is either:

(1) You could try and set the color key to RGB(255, 255, 255) and hope that you don't have any white pixels in your transparent GIFs. This way they will load correctly with GapiDraw 1.03 without having to modify them
(2) Batch convert all images into another format.

By the way.. You are aware that a license is required if you want to use GIF images in your product? It is very simple to scan your file for GIF images, and it is currently done by robots on the Internet. I would strongly suggest that noone uses GIF images for anything really, both due to the patent and now also since the GIF decoder in all Pocket PCs are corrupt.
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Postby Kzinti » Jun 29, 2002 @ 11:18pm

This patent on GIF is exactly the reason why you should use imgdecmp.dll to decompress your GIF images... Microsoft as a license for it's decompression code.
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Postby Johan » Jun 29, 2002 @ 11:36pm

Ok. I did some reading on the issue and apparantly it's ok to use and distribute GIF files freely, but not to develop an own GIF compressor/decompressor without permission. I thought commercial use of GIF images as such was forbidden..

By the way. Have you found any solution to the masking issues of IMGDECMP.DLL? Setting crTransparentOverride won't work. I also tried using a custom DC for palette in the DecompressImageInfo but it made no difference. Neither does changing the color depths...
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