 | [TOC] Chapter 11: Light Sources |  |
Light sources play a critical role in ray tracing as they determine how light interacts with objects in a scene, affecting the overall illumination and appearance of surfaces. In ray tracing, light emission is modeled to simulate various types of light sources, each contributing differently to the rendering process. Here, we will explore the concepts of light emission, different types of lights, and how to implement them in JavaScript.
In ray tracing, light sources are entities that emit light, illuminating objects in a scene and influencing their appearance based on the material properties. The interaction of light with surfaces defines how they are shaded and how shadows are cast. Ray tracing simulates the path of light as rays that bounce off surfaces, providing realistic rendering of images.
| Light Emission | |
Light emission refers to the way light is generated and emitted from a source. In ray tracing, this is typically quantified using a radiance function that describes how light intensity varies with direction and wavelength. The radiance \( L \) can be mathematically expressed as:
\[
L(\theta, \phi) = \frac{d^2\Phi}{dA \, d\omega}
\]
where:
\( d\Phi \) is the amount of light emitted,
\( dA \) is the area from which light is emitted,
\( d\omega \) is the solid angle.
| Implementing Lights | |
To implement light sources in a ray tracing system, we typically define a base class for lights, from which specific types of lights will inherit. Each light type will have its own methods to calculate the light intensity and contribution to a pixel based on its position, direction, and other properties.
Here's a basic JavaScript implementation for a light source base class:
class Light {
constructor(position, intensity) {
this.position = position; // Position of the light
this.intensity = intensity; // Intensity of the light
}
// Method to get the light intensity at a point in space
getIntensity(point) {
// Calculate the direction from the light to the point
const direction = point.subtract(this.position).normalize();
return this.intensity;
}
}
| Point Lights | |
Point lights are light sources that emit light uniformly in all directions from a specific point in space. They are often used to simulate light bulbs or similar sources. The intensity at a point is typically attenuated based on distance.
The intensity can be computed as follows:
\[
I = \frac{I_0}{d^2}
\]
where:
\( I_0 \) is the initial intensity,
\( d \) is the distance from the light to the point.
Here's a JavaScript implementation of a point light:
class PointLight extends Light {
constructor(position, intensity) {
super(position, intensity);
}
getIntensity(point) {
const direction = point.subtract(this.position);
const distance = direction.length();
const intensityAtPoint = this.intensity.scale(1 / (distance * distance));
return intensityAtPoint;
}
}
| Distant Lights | |
Distant lights (or directional lights) emit parallel rays of light, similar to sunlight. They have no specific position; instead, they are defined by a direction. This is useful for simulating sunlight where all rays are parallel.
The intensity is simply:
\[
I = I_0
\]
Here's how you could implement a distant light in JavaScript:
class DistantLight extends Light {
constructor(direction, intensity) {
super(null, intensity);
this.direction = direction.normalize(); // Direction of the light
}
getIntensity() {
return this.intensity; // Directional lights have uniform intensity
}
}
| Area Lights | |
Area lights are defined by a surface area and emit light from that surface. They provide softer shadows compared to point or distant lights, simulating realistic light sources like lamps or windows.
The intensity can be computed based on the area and the position of the light relative to the point being illuminated.
A simple implementation for an area light might look like this:
class AreaLight extends Light {
constructor(position, intensity, area) {
super(position, intensity);
this.area = area; // Surface area of the light
}
getIntensity(point) {
const direction = point.subtract(this.position);
const distance = direction.length();
const intensityAtPoint = this.intensity.scale(1 / (distance * distance));
return intensityAtPoint.scale(this.area); // Scale by area
}
}
| Infinite Area Lights | |
Infinite area lights act like area lights but are considered to extend infinitely in one direction. They can simulate large surfaces like the sky or an infinitely large wall.
They provide a uniform light intensity across the entire scene.
Here's how you might implement an infinite area light:
ript
class InfiniteAreaLight extends Light {
constructor(direction, intensity) {
super(null, intensity);
this.direction = direction.normalize();
}
getIntensity(point) {
// Assume uniform light across the scene
return this.intensity;
}
}
|
