Re: png images in tool-bar / alpha mask

[David Reitter]

On 6 Apr 2008, at 03:52, YAMAMOTO Mitsuharu wrote:

> This is not the only place where NULL-check of img->mask is used for
> determining the existence of the image mask.  At least, xdisp.c and
> macterm.c also assume that.

Yes, but doesn't that happen in order to check whether there is a  
bitmap mask that will be used for something?

x_draw_image_foreground actually uses that mask to draw the image, and  
my understanding is that we want to use the original (platform  
specific) image data for that, including its alpha channel.  As we  
can't do that (yet) on X or W32, we don't set the platform specific  
image data in the first place there.
In macterm.c, we want to call mac_copy_area rather than  
mac_copy_area_with_mask, right?

In x_draw_image_foreground (macterm.c), it is always safe to draw a  
rectangle around given that we don't know what the alpha channel  
specifies, but one could go through Fimage_mask_pp to get the same  
semantics.

As for image.c: I don't understand all of the code.  In general, it  
appears safe to assume we don't have a mask on the C level.

The alternative would be to acquire a bitmap mask from the PNG when  
loading it. Maybe that would be cleaner.

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