Spinning Ring

Rotate polar angle and colorize a ring.

Overview

• Use polar angle as a gradient factor.

Learning Objectives

• Animate with u_time

Prerequisites

• uv-coordinates

Inputs

• float u_time — Time in seconds.

Key Concepts

• Angle comes from atan(y, x).

float a = atan(p.y, p.x);

• Normalize angle to [0,1] and use it as a factor.

float t = (a + PI) / (2.0 * PI);

How To Implement (Step-by-step)

• Center coordinates: p = vUv - 0.5.
• Angle: a = atan(p.y, p.x).
• Normalize: t = (a + PI) / (2*PI).
• Use t to mix colors.

Self-check

• Does it compile without errors?
• Does the output match the goal?
• Are key values kept in [0,1]?

Common Mistakes

• Clamp t into [0,1] when needed.
• Make sure edge0 < edge1 for smoothstep().