#312 No alpha support in XPM display driver

[renderguy]

It seems Aqsis is missing alpha-channel support when using the XPM display driver.

IIRC my scene contained an imager shader, which I think has highlighted problems with other display drivers before.

This was tested with Windows XP x64 (SVN revision 2202).

[Michel Joron]

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xpm format doesn't support rgba we could only specify a transparent color, a bit like the old 'gif' format.

Most of the drawing package will do usually a median cut at 50% to put the transparent colours to be fully transparent while saving (eg. gimp). We could do the same in this driver but we probably required to add one extra more parameter to xpm driver to specify the alpha cut-off point.

[renderguy]

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I think adding an argument to the XPM display driver would be useful, something like...

Display "myfile.xpm" "xpm" "rgba" "string threshold" "#000000"

In my mind the above should be the default colour (black) used when specifying "rgba" without any further parameters to this display.

[Chris Foster]

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To be honest, I'm not sure this is worth implementing: I think we should ask ourselves who is really going to use such a feature? There are a bunch of great open source tools which can be used to convert between image formats; if somebody desperately needs a transparent XPM they can generate tiff and convert to XPM from there.

I don't imagine that anybody would seriously consider XPM as an intermediate format for any real graphics work.

~Chris.

[Chris Foster]

I'm going to close this bug in the interests of keeping the bug list clean, since it doesn't really seem worth fixing. Feel free to reopen as a feature request if you must.