Mouse Interaction

Learn to create interactive effects using mouse coordinates and understand the passing and usage of uniform variables.

Overview

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

Learning Objectives

• Understand how to receive and use mouse coordinates (u_mouse) in GLSL.
• Learn to dynamically change shader output based on mouse position.
• Master the method of passing data between CPU and GPU using uniform variables.

Prerequisites

• uv-coordinates
• uniforms

Inputs

• vec2 u_resolution — Canvas size in pixels.
• vec2 u_mouse — Mouse position in pixels.
• float u_time — Time in seconds.

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)

• mouse = u_mouse / u_resolution
• distToMouse = distance(uv, mouse)
• mouseColor = vec3(mouse, 0.5)
• pulse = sin(u_time * speed) * 0.5 + 0.5

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.
• Don’t use raw pixels without normalization.
• Make sure edge0 < edge1 for smoothstep().