Twister

A classic demoscene effect from the 1990s. The twister creates the illusion of a 3D rectangular bar that twists along its vertical axis while rotating.

How It Works

The twister effect renders a rectangular bar that appears to twist in 3D space:

1. Segmentation: The bar is divided into horizontal slices (segments)
2. Twist angle: Each segment has a rotation angle that varies with vertical position, creating the twist
3. Perspective: Simple Z-based perspective scaling makes closer parts appear larger
4. Face sorting: The 4 faces of the bar are sorted back-to-front for correct rendering
5. Shading: Faces are shaded based on their orientation (Z depth)
6. Animation: The base rotation angle increments over time, creating continuous rotation

The key formula for the twist is:

Where y_norm is the normalized vertical position (-0.5 to 0.5), twists is the number of full rotations along the bar, and t is the animation time.

Classic Demo Scene

This effect was popularized in the demo scene of the early 1990s, particularly on the Amiga and later on DOS PCs. It showcased the ability to create convincing 3D graphics using clever 2D rendering tricks—all without hardware 3D acceleration.

The wavy motion adds extra visual interest, simulating the bar wobbling as it rotates.