SVG Optimizer

The file is taken apart into markup tokens by the same lexer this site's XML formatter uses, rather than searched with patterns, and every rule then acts on a thing it can actually identify. That matters because the previous version was a stack of about a dozen regular expressions, and measured against the only reference an optimiser has, which is rendering both files and counting the pixels that moved, it failed in four separate ways. An Inkscape export came out UNRENDERABLE at every preset including the one called Safe: the attribute-stripping pattern ran greedily past an element name to the first equals sign and turned a self-closing sodipodi:namedview into a stray angle bracket, which a browser refuses to draw. A file using ordinary SVG features lost 14,986 of 102,400 pixels at the default preset, 14.63 percent, worst channel 255. And two checkboxes, Remove Unused Defs and Shorten Ids, were rendered, set by presets, and read by nothing.

Each of those has the same cause and the same fix. Whitespace is now removed only from text nodes that are whitespace and NOTHING else, which is the one rule XML has without a schema, so a text element keeps its double spaces and xml:space="preserve" is honoured. Comments are removed as comment nodes, so the characters that look like a comment inside a text element survive. Numbers are rounded only in attributes whose value really is a number (the path data, the coordinates, the transforms, the viewBox), so a document that prints pi to eight places still prints pi to eight places. Colours are shortened only in attributes that really hold a colour, so id="red" is left alone, and an eight-digit #RRGGBBAA is left alone too: the old pattern matched its first six digits and turned #aabbccdd into #abcdd, a different colour with a different alpha. Both dead options now work, and shortening an id rewrites every url(#...) that refers to it in step.

After every change the page does the thing the copy used to merely assert: it draws both files at 320 by 320 and compares every pixel, and says either that not one of the 102,400 changed or exactly how many did and by how much on the worst channel. On the four corpus files the safe preset now changes zero pixels every time, where the old one made one of them unrenderable. Because the check exists, a new button becomes possible: try every coordinate precision from 6 down to 0, render each, and select the smallest one whose output is pixel identical. On one test file that is five decimal places, a saving the default three would have taken at the cost of 194 moved pixels.

One rule changed on principle rather than on a measurement. A title element is the accessible NAME of an SVG and desc is its description (SVG 1.1 section 5.4), and the old tool removed both at every preset. They are kept by default now; the aggressive preset still removes them, and says what that costs. The output is also checked for well-formedness with a line, a column and the specific problem, and every rule that fired is listed with what it removed and how many bytes it saved, so the saving is attributable rather than a single percentage.