[PATCH] Use GDAL transparency masks

[rouault]

From GDAL >= 1.5.0, the concept of transparency mask has been introduced. See ​RFC 15.

This patch uses dataset transparency masks when no alpha band is available. It reads the mask band and simulates as if it was an alpha band, so the impact on existing code is minimum.

[rouault]

To test with "./shp2img -m transparency_mask.map -o result.tif -l TEST -s 200 200 -e 0 0 19 19"

[rouault]

Grey level image with transparency mask

[rouault]

RGB image with transparency mask

[rouault]

Note : the above attached TIFF images have internal transparency masks, that are only handled on GDAL trunk >= r14647.

[rouault]

Expected result : grey square at the centre of a red background

[sdlime]

Changing component to "GDAL Support"... I can apply but would like Frank's blessing.

Steve

[rouault]

I've discovered the existence of msautotest/gdal, and of course by testing it, I discovered that my patch introduced a regression in unclassified.map, where the PROCESSING "BANDS=1,2,3" directive excludes the alpha component of the RGBA image from being taken into account. So I'm updating the patch not to try to use transparency masks when the BANDS keyword is used in PROCESSING. This way the test suite passes fine again.

Patch updated.

[rouault]

Patch to use GDAL transparency masks (updated not to be triggered with BANDS keyword)

[warmerdam]

I have incorporated a slight variation on the patch in trunk (r10002).

[warmerdam]

Implemented test in test suite based on provided sample files (r10003) and incorporated the check for GDAL 1.5 or newer (r10004).

Thanks Even - sorry for the delay in incorporating.