Links (web Browser) - Graphics Stack

Graphics Stack

The graphics stack has several peculiarities unusual for a web browser. The fonts displayed by Links are not derived from the system, but compiled into the binary as grayscale bitmaps in PNG format. This allows the browser to be a single executable file independent of the system libraries, however it increases the size of the executable to about 5 MB.

The fonts are anti-aliased without hinting and for small line pitch an artificial sharpening is employed to increase legibility. Subpixel sampling further increases legibility on LCD displays. This allowed Links to have anti-aliased fonts at a time when anti-aliased font libraries were uncommon.

All graphical elements (images and text) are first converted from given gamma space (according to known or assumed gamma information in PNG, JPEG etc.) through known user gamma setting into a 48 bits per pixel photometrically linear space where they are resampled with bilinear resampling to the target size, possibly taking aspect ratio correction into account. Then the data are passed through high-performance restartable dithering engine which is used regardless of monitor bit depth, i. e. also for 24 bits per pixel colour. This Floyd–Steinberg dithering engine takes into account the gamma characteristics of the monitor and uses 768 KiB of dithering tables to avoid time expensive calculations. A technique similar to self-modifying code, function templates, is used to maximize the speed of the dithering engine without using assembler optimization, which is non-portable.

Images which are scaled down also use subpixel sampling on LCD to increase level of detail.

The reason for this high quality processing is: provide proper realistic up/downsampling of images, and photorealistic display regardless of the monitor gamma, without colour fringing caused by 8-bit gamma correction built into the X server. It also increases the perceived colour depth over 24 bits per pixel.

Despite the amount of digital image processing that has to be internally done, Links is one of the fastest graphical web browsers.

Links has graphics driver for X Server, Linux framebuffer, svgalib, OS/2 PMShell and AtheOS GUI. This allows it to run in graphics mode even on platforms which don't have X Server because of lack of implementation or limited resources.