🚀 go-pugleaf

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There are several algorithms for doing this, all based on a "scanline"
method.  The basic idea is to skew the image first in the X direction,
then in the Y direction.  You can accomplish a rotation up to 45deg
with this technique.  To get rotations > 45 degrees, you first rotate
by a multiple of 90 (easily accomplished).  Some references:
	Catmull, E. and Smith, A.R., "3-D Transformations of Images in
	Scanline Order", Computer Graphics, Vol 14, No 3, July 1980
	(SIGGRAPH '80 Conference Proceedings).

	Fant, K., "A Nonaliasing, Real-Time Spatial Transform
	Technique", IEEE Computer Graphics and Applications, January
	1986, (See also Letters to the Editor, IEEE CG&A, March 1986
	and July 1986.)

	Paeth, A., "A Fast Algorithm for General Raster Rotation",
	Graphics Interface '86 Proceedings, May 1986.

I will attempt a picture demonstrating the technique:

.............. 	                 ..............           ....
.            . 	 	       	.	     .           .    ...
.            . 	 X skew	       . 	    .  Y skew  ..        ...
.            . 	 ------>      .	 	   .   -----> .             ...
.            .		     .	          .          ...               ..
.            .		    .	         .              ...           ..
..............             ..............                  ...       .
                                                              ...  ..
                                                                 ..

=Spencer   ({ihnp4,decvax}!utah-cs!thomas, thomas@cs.utah.edu)