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From: lim@.cs.umass.edu
Newsgroups: comp.windows.x
Subject: Question: Rendering rotated text - shear transformation algorithm
Message-ID: <31883@dime.cs.umass.edu>
Date: 11 Jun 91 20:55:23 GMT
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Reply-To: lim@.cs.umass.edu ()
Organization: University of Massachusetts, Amherst
Lines: 36

>Subject: 119)* How do I render rotated text?
>	
>	Xlib intentionally does not provide such sophisticated graphics 
>capabilities, leaving them up to server-extensions or clients-side graphics
>libraries.
>	Your only choice, if you want to stay within the core X protocol, is to
>render the text into a pixmap, read it back via XGetImage(), rotate it "by
>hand"
>with whatever matrices you want, and put it back to the server via XPutImage();
>more specifically:
>	1) create a bitmap B and write your text to it.
>	2) create an XYBitmap image I from B (via XGetImage).
>	3) create an XYBitmap Image I2 big enough to handle the transformation.
>	4) for each x,y in I2, I2(x,y) = I(a,b) where 
>		a = x * cos(theta) - y * sin(theta)
>		b = x * sin(theta) + y * cos(theta)
>	5) render I2
>	Note that you should be careful how you implement this not to lose
>bits; an algorithm based on shear transformations may in fact be better.
>	The high-level server-extensions and graphics packages available for X 
>also permit rendering of rotated text: Display PostScript, PEX, PHIGS, and GKS,
>although most are not capable of arbitrary rotation and probably do not use the
>same fonts that would be found on a printer.
>	In addition, if you have enough access to the server to install a font
>on it, you can create a font which consists of letters rotated at some
>predefined angle. Your application can then itself figure out placement of each
>glyph.

Hi,

I'd appreciate it if anyone could provide more information about the shear
transformation algorithm. Thanks.


Jonathan Lim
lim@cs.umass.edu