In order to implement native gradient skew, I have to use an affine transformation. This motivated me to look for affine transformations already implemented in PLplot, and as expected we have tons of them as well as the capability to communicate coordinate transformations to many external libraries (and also the SVG specification for the svg device driver) via affine transformations. However, nowhere in PLplot could I find elementary affine transform utilities so I have just implemented those in plaffine.c (revision 10685). Those utilities build without issues, and I intend to start using these utilities where appropriate in PLplot in the interest of understanding exactly what elementary transformations go into any affine transformation matrix that is determined (e.g., in calc_diori) and in the interests of speed (it is much faster to multiply affine transformation matrices and apply the transformation once with the product matrix rather than to repeat the transformation for each individual affine matrix as is currently done in difilt and sdifilt).
In the interest of clarity and standardization, if you are reviewing or creating any piece of core or driver code from now on that uses coordinate transformations, please consider using the affine utilities. Note, the utilities adopt the SVG specification convention that the axes are affected by the translation, scaling, rotation, x-skew, and y-skew. However, all our affine transformations are the inverses of the equivalent SVG ones because their (post-multiplied product) affine matrix operates on the new coordinates to obtain the old coordinates while our (pre-multiplied product) affine matrix operates on the old coordinates to obtain the new ones. Alan __________________________ Alan W. Irwin Astronomical research affiliation with Department of Physics and Astronomy, University of Victoria (astrowww.phys.uvic.ca). Programming affiliations with the FreeEOS equation-of-state implementation for stellar interiors (freeeos.sf.net); PLplot scientific plotting software package (plplot.org); the libLASi project (unifont.org/lasi); the Loads of Linux Links project (loll.sf.net); and the Linux Brochure Project (lbproject.sf.net). __________________________ Linux-powered Science __________________________ ------------------------------------------------------------------------------ Join us December 9, 2009 for the Red Hat Virtual Experience, a free event focused on virtualization and cloud computing. Attend in-depth sessions from your desk. Your couch. Anywhere. http://p.sf.net/sfu/redhat-sfdev2dev _______________________________________________ Plplot-devel mailing list Plplot-devel@lists.sourceforge.net https://lists.sourceforge.net/lists/listinfo/plplot-devel
