10.5 - Ambient Lighting¶

An Ambient Lighting Model¶

Ambient light is “background” light. It bounces everywhere in all directions and comes from no specific light source. Ambient light illuminates every face of a model regardless of the face’s orientation to a light source. All faces get the same amount of ambient light.

Ambient light is modeled as a RGB value, where each component represents a percentage of color that is visible. For example, the ambient light value (0.2, 0.2, 0.2) means that 20% of a surface’s color is visible, while (0.5, 0.5, 0.5) means that 50% of a surface’s color is visible. For white background light the component values are all the same. However, you can bring out one color over others by using independent values. An ambient value of (0.5, 0.1, 0.1) would give the impression that a scene has a red light source somewhere in the background.

The Math for Ambient Light¶

The math for ambient light is trivial. An RGB value that represents the color of a surface is multiplied by the ambient percentages to calculate a pixel’s final color.

A WebGL Program for Ambient Light¶

Experiment with the following WebGL program by modifying the ambient light percentages. You can manipulate the percentages independently, or all at the same time.

As you experiment with the WebGL program above, please make sure you observe the following characteristics of ambient light.

• The relative position of an object, a light source, and/or a camera has no impact on ambient lighting.
  
  
• Ambient lighting is a percentage of a surface’s color that is visible from any direction. Ambient light can never make a surface’s color “brighter”; it can only make a surface’s color “darker”. The purpose of ambient lighting is not to make surfaces “darker,” but rather to make sure that a certain percentage of a surface’s color is always visible, even if it has no direct light from a light source.
  
  
• White background light uses the same value for each component of the ambient percentages. This maintains the relative color of objects in a scene. However, you can simulate a “background” light of any color to create special effects.
  
  
• Ambient lighting is typically not used by itself. It is typically combined with diffuse and specular lighting. This will be demonstrated in the next lesson.

Ambient Lighting in Shader Programs¶

Please study the following shader programs and their explanations.

 1
 2
 3
 4
 5
 6
 7
 8
 9
10
11
12
13
14
15
16
17
18
19
20
21
22
23
24
25

// Vertex Shader
precision mediump int;
precision mediump float;

// Scene transformations
uniform mat4 u_PVM_transform; // Projection, view, model transform

// Light model
uniform vec3 u_Ambient_color;

// Original model data
attribute vec3 a_Vertex;
attribute vec3 a_Color;

// Data (to be interpolated) that is passed on to the fragment shader
varying vec4 v_Color;

void main() {

  // Pass the vertex's color to the fragment shader.
  v_Color = vec4(a_Color, 1.0);

  // Transform the location of the vertex for the graphics pipeline.
  gl_Position = u_PVM_transform * vec4(a_Vertex, 1.0);
}

 1
 2
 3
 4
 5
 6
 7
 8
 9
10
11
12
13
14
15
16
17
18
19
20

// Fragment shader program
precision mediump int;
precision mediump float;

// Light model
uniform vec3 u_Ambient_color;

// Data coming from the vertex shader
varying vec4 v_Color;

void main() {

  vec3 color;

  // Vector, component-wise multiplication
  color = u_Ambient_color * vec3(v_Color);

  // Ambient color does not affect the alpha value of the object's color.
  gl_FragColor = vec4(color, v_Color.a);
}

Type of Light Source¶

Ambient lighting is not based on the type of light sources in a scene. Therefore, the example WebGL program above would be the same for any scene with any type of light sources.

Glossary¶

ambient lighting

Light that can’t be associated with any specific light source. It is light that has no associated location or direction.

Self Assessment¶