Bitmap with transparency mask

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Is it possible in C++ builder to use a monochrome bitmap as a transparency mask? I know builder has transparency feature, but I want some places to be more transparent than others.
Thank you, Daniel :)

Posted 18-May-10 0:41am

xspitfirexx

Updated 18-May-10 0:45am

Moak

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Sauro Viti · Answer 1 · 2010-05-19T04:54:00

I'm not experienced on C++ builder, however transparency features are usually implemented basing on the underlying OS support.

Microsoft Windows could handle transparency in two ways:

thru GDI, by setting a specific RGB color as transparent. This way each pixel of the given color is treated as completely transparent and other pixels will be completely opaque

thru GDI+, by using images with a valid alpha channel. This ways each pixel has 4 bytes associated with it: the red, green, blue and alpha values. The alpha value of each pixel determine how that pixel is opaque: a value of 0 mean that the pixel is completely transparent and a value of 255 means that the pixel is completely opaque

Said that, you can use GDI+ to render a semi-transparent image, and if you want to use a gray-scale bitmap as transparency mask, you should first load your image on a GDI+ context, then modify each pixel to set their alpha value to the value of the correspondant pixel from the gray-scale bitmap.