SDF Ring

Draw a ring using a distance field: abs(length(p) - r) and smoothstep for smooth edges.

Overview

• Use a distance field and a mask to shape the image.

Learning Objectives

• Understand distance fields as shape boundaries.
• Build a ring distance with abs(length(p) - r).
• Use smoothstep for anti-aliased / soft edges.

Prerequisites

• simple-circle
• smooth-edges

Key Concepts

• Distance to center builds a distance field.

vec2 p = vUv - 0.5;
float d = length(p);

• Convert distance into a mask.

float mask = 1.0 - smoothstep(r, r + aa, d);

How To Implement (Step-by-step)

• Center coordinates: p = vUv - 0.5.
• Compute distance: d = length(p).
• Build a mask with smoothstep or step.
• Mix foreground/background by the mask.

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().