Simple Rectangle

Learn to draw rectangles using conditional statements and understand coordinate ranges and boundary detection.

Overview

• Implement a horizontal gradient using UV as the factor.

Learning Objectives

• Understand how to use logical AND (&&) to combine conditions to define a rectangular area.
• Learn to perform boundary detection based on the x and y values of UV coordinates.
• Master drawing simple shapes in GLSL using conditional statements (e.g., if or step).

Prerequisites

• uv-coordinates
• solid-color

Inputs

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

Key Concepts

• Normalize pixel coordinates to UV.

vec2 uv = gl_FragCoord.xy / u_resolution.xy;

• A horizontal gradient uses a 0-1 factor (usually UV) to blend colors.

float t = uv.x;
vec3 color = vec3(t);

• Keep the factor inside [0,1].

t = clamp(t, 0.0, 1.0);

How To Implement (Step-by-step)

• Normalize coordinates: uv = gl_FragCoord.xy / u_resolution.xy.
• Set factor: t = uv.x.
• Map t to a color (grayscale or mix).
• Output gl_FragColor with alpha=1.

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.