Vignette (Edge Darkening)

This is the Module 3 capstone. Combine distance from center with smoothstep to darken the edges — that's a vignette.

The approach

1. Compute each pixel's distance from the canvas center
2. Greater distance means closer to the edges
3. Use smoothstep to turn distance into a 0–1 mask: 1 at center (bright), 0 at edges (dark)

• d < 0.25: v = 1 (center, fully bright)
• d > 0.6: v = 0 (corners, fully dark)
• in between: smooth transition

Using the mask to mix colors

Exercise

The exercise has v = 1.0 (all bright, no vignette). Use 1.0 - smoothstep(0.25, 0.6, d) to compute the vignette mask v.

Answer Breakdown

smoothstep(0.25, 0.6, d) starts rising at d=0.25 and reaches 1 at d=0.6. The 1.0 - inverts: bright at center, dark at edges.

• Smaller 0.25 → vignette starts closer to center
• Smaller 0.6 → narrower transition, harder edge
• Larger 0.6 (e.g. 1.0) → softer, gentler vignette