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Re: Image size, DPI (was Re: Gorm is broken)

From: Riccardo Mottola
Subject: Re: Image size, DPI (was Re: Gorm is broken)
Date: Sat, 07 May 2011 14:26:28 +0200
User-agent: Mozilla/5.0 (X11; U; FreeBSD i386; en-US; rv: Gecko/20101113 SeaMonkey/2.0.10

Yes. However, the value 72 dpi is important in GNUstep/Cocoa because 1 point in 
the window's base coordinate system = 1 pixel, and a point is 1/72 inch. (even 
though it's an arbitrary number in some sense because no modern desktop screens 
are really as low resolution as 72 PDI).

So drawing an image with 1 pixel = 1 pixel means treating the image as if it is 
72 DPI, which is what the code did before my patch, i.e. it set the dimensions 
in points to the dimensions in pixels.

I just checked on Cocoa and it ignores the dpi of PNG's and assumes them to be 
72dpi, however it reads and uses the dpi of TIFF's exactly as GNUstep does now. In 
addition, Cocoa supports multi-image TIFF's, something I would like to add support 
for to GNUstep. This means we can provide high-res versions of the default artwork 
which are only used when a scale factor>  1 is set.

I took Terminal's icon and UI elements and explicitly set them to 72dpi. The Icon seems to draw quite well, the UI icons in the preferences (the cursor buttons) seem to be slightly blurred, as if drawing was scaled by a factor close to 1, but not being 1.


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