that reflect or refract underlying bitmap images Texture-mapped tunnel with freely moving camera, typically based on realtime raytracing Rotozoomer Mandelbrot zoomer Fire effect and other effects based on 2D filters and feedback Heightfield landscape (often called "voxel landscape") 2D bump mapping Metaballs Some of these effects were later ported to planar pixel machines such as the Amiga, without relying on chunky to planar conversion. For example, the group Sanity implemented a rotozoomer using a combination of pre-rendered planar bitmaps and copper effects. 3D rendering 3D computer graphics has been featured in demos since the late 1980s. Nowadays, a general-purpose 3D engine is an integral part of most new demos. In the late 1980s and early 1990s, rotating 3D objects were considered effects in their own right due to the difficulty of calculating and rendering them. In particular, most systems did not have a floating point unit. Rather than general-purpose 3D algorithms, democoders often used special-purpose tricks highly optimized for the rotation and rendering of a particular object such as a cube or a sphere. Since even drawing dots, lines or filled polygons was a difficult task in itself competition often revolved around simply optimising the drawing routines while using pre-calculated maths. To a casual viewer, many demo effects look like something attainable by a general-purpose 3D engine. However, classic effects with an apparent 3D look often have no real-time 3D calculation whatsoever. For example, static screen-to-texture look-up tables can be used with symmetrical 3D objects that rotate around their axis of symmetry. Before the advent of mass-marketed 3D acceleration hardware, democoders often focused on lighting and shading techniques in software 3D engines, including Gouraud shading, Phong shading, texture mapping, bump mapping, environment mapping, radiosity and even real-time ray tracing. General-purpose 3D engines are very seldom called "effects", although the rendered scenes often contain something that can be regarded as such. See also Display hack Algorithmic art References Demoscene