{"id":30,"date":"2017-06-23T13:26:55","date_gmt":"2017-06-23T13:26:55","guid":{"rendered":"https:\/\/blogs.scummvm.org\/joefish-gsoc\/?p=30"},"modified":"2022-05-21T14:09:22","modified_gmt":"2022-05-21T14:09:22","slug":"image-rendering-and-animation","status":"publish","type":"post","link":"https:\/\/blogs.scummvm.org\/joefish-gsoc\/2017\/06\/23\/image-rendering-and-animation\/","title":{"rendered":"Image Rendering and Animation"},"content":{"rendered":"
\"\"<\/a>
Let’s hope not all humans are that ugly — probably some Axacutian<\/figcaption><\/figure>\n

This post will be about the compression algorithm used for the graphics and how it plays into the animation system of Supernova.<\/p>\n

The images consist of a custom palette of 239 colors and divided up into sections that define its size and a pointer to the image data. An exception to this are the newspaper articles, seen in the intro of the game.<\/p>\n

\"\"<\/a>Those bitmap images have dimensions of 640×480 and only monochrome colors, instead of 256-colors palettized 320×200. The difference in their encoding can be seen here in the code<\/a>. So, for the mode 0x11 images I mask the bits of a byte and depending if the bit is set 0 (Black) or 11 (63% White) is written. It is safe to use palette colors as the first 16 colors of the default palette, defined here<\/a>, won’t be overwritten by an image’s custom palette.<\/p>\n

Mode 0x13 images that make up the rest of the game’s graphics are compressed in a run-length encoding (RLE) and are 320×200 256-color palettized. The following describes the structure of the file format:<\/p>\n

\"\"<\/a>The image decoding part can be found here<\/a>. It works more or less like this:<\/p>\n

The encoded image is read into a variable ‘input’ byte by byte<\/p>\n