I took some time to actually understand the perspective transformations properly using the excellent ImageMagick examples (mainly created by Anthony Thyssen) as a reference. The basic idea of perspective distortion seems simple: to distort the control points to new locations.

His example uses a checkerboard as the image to manipulate and, based on an array of settings (source, destination) sets control points for the image to twist and turn from. The final output is echoed from a call to distortImage.

Look no further than this patch to the PHP XSL extension. It uses the built in profiler of libxslt to get the information which template was called how many times and how much time was spent in them. It may help in improving the speed of your XSLT transformations, like a PHP debugger can help in profiling your PHP scripts.

Besides the link, he also includes a simple sample script that uses the setProfiling function to write out to a text file the stats of the transformation. He also includes a (very beta) patch to the libxslt functionality itself to make it easier to not only time the overall execution of the xslt, but also allows for timing of other individual templates that might be included.

Without going into theoretical details, some of which are quite alien to me, I'll try to describe some of the challenges that pattern patching rewriting macros might pose for a language like php. After brief explanation what kind of a beast is this, I try to explore some of the finer points, which might cause problems. The intent of this post is to sketch a design and highlight some of the possible issues.

He breaks up the post into a few sections:

• pattern matching rewrite only macros - a bird eye view
• Transformation time
• Basic/skeleton shapes and intermediate shapes
• Code generation issues specific to php
• Hygiene
• A rough macro shape outline
• Output/Status of the project