Solid Color Fill

Learning Objectives

Learn the basic structure of GLSL fragment shaders and understand how to set solid colors.

Core Concepts

Fragment Shader Basics

- Fragment Shader: Runs for each pixel, determining the final color

- gl_FragColor: The output variable that sets the pixel color

- vec4: A 4-component vector representing RGBA color values

Color System

- RGBA: Red, Green, Blue, Alpha (transparency)

- Value Range: Each component ranges from 0.0 to 1.0

- Color Representation: (1.0, 0.0, 0.0, 1.0) represents opaque red

Related Functions and Syntax

vec4 Constructor

`glsl

vec4(r, g, b, a) // Create a 4-component color vector

vec4(0.5) // Create a gray color (0.5, 0.5, 0.5, 0.5)

vec4(rgb, a) // Combine vec3 RGB with alpha

`

Color Assignment

`glsl

gl_FragColor = vec4(1.0, 0.0, 0.0, 1.0); // Red

gl_FragColor = vec4(0.0, 1.0, 0.0, 1.0); // Green

gl_FragColor = vec4(0.0, 0.0, 1.0, 1.0); // Blue

`

Code Analysis

`glsl

precision mediump float;

void main() {

gl_FragColor = vec4(1.0, 0.0, 0.0, 1.0);

}

`

Line-by-line explanation:

1. precision mediump float; - Sets floating-point precision (required in fragment shaders)

2. void main() { - Main function entry point

3. gl_FragColor = vec4(1.0, 0.0, 0.0, 1.0); - Sets pixel color to opaque red

4. } - End of main function

Practice Tips

1. Try Different Colors:

- vec4(0.0, 1.0, 0.0, 1.0) - Green

- vec4(0.0, 0.0, 1.0, 1.0) - Blue

- vec4(1.0, 1.0, 0.0, 1.0) - Yellow

- vec4(1.0, 0.0, 1.0, 1.0) - Magenta

2. Experiment with Alpha:

- vec4(1.0, 0.0, 0.0, 0.5) - Semi-transparent red

- vec4(0.0, 0.0, 0.0, 0.0) - Fully transparent

3. Use Intermediate Values:

- vec4(0.5, 0.5, 0.5, 1.0) - Gray

- vec4(0.8, 0.2, 0.4, 1.0) - Custom pink

Common Variations

Grayscale Colors

`glsl

gl_FragColor = vec4(0.5); // Equivalent to vec4(0.5, 0.5, 0.5, 0.5)

gl_FragColor = vec4(vec3(0.7), 1.0); // Gray with full opacity

`

Using Constants

`glsl

const vec3 RED = vec3(1.0, 0.0, 0.0);

gl_FragColor = vec4(RED, 1.0);

`

Extended Thinking

1. Why use 0.0-1.0 range? This normalized range makes calculations easier and is hardware-friendly

2. What happens with values > 1.0? They get clamped to 1.0

3. Performance considerations: Simple solid colors are very fast to render

4. Real-world applications: UI backgrounds, solid overlays, color swatches

Next Steps

Once you master solid colors, you can move on to:

- Color mixing and interpolation

- Using coordinates to create gradients

- Time-based color animation

- Texture sampling and color manipulation