Aspect-Ratio Corrected UV

Learn to correct UV aspect ratio with u_resolution so circles stay round on non-square canvases.

Overview

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

Learning Objectives

• Understand how canvas aspect ratio affects shapes.
• Compute aspect from u_resolution and correct coordinates.
• Draw an undistorted circle using a distance field (length).

Prerequisites

• uv-coordinates

Inputs

• vec2 u_resolution — Canvas size in pixels.

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().