What are the best techniques for implementing realistic shadows in your scenes?

1 Shadow Mapping

Shadow mapping is one of the most common and widely used techniques for creating shadows. It works by rendering the scene from the light source's point of view and storing the depth values in a texture, called the shadow map. Then, for each pixel in the final image, it compares the depth value from the camera's point of view with the depth value from the shadow map. If the camera's depth is greater, the pixel is in shadow. Shadow mapping is fast and easy to implement, but it also has some drawbacks, such as aliasing, resolution issues, and self-shadowing artifacts.

2 Shadow Volumes

Shadow volumes are another popular technique for creating shadows. It works by extruding the silhouette edges of the objects in the scene along the direction of the light source, forming volumes that enclose the shadowed regions. Then, for each pixel in the final image, it counts how many times it crosses the shadow volumes, using a stencil buffer. If the count is odd, the pixel is in shadow. Shadow volumes are accurate and robust, but they also have some drawbacks, such as high geometric complexity, fill-rate limitations, and light leaking problems.

3 Ray Tracing

Ray tracing is a technique for creating shadows that simulates the physical behavior of light. It works by tracing rays from the camera to the scene, and checking if they intersect with any objects. If a ray hits an object, it generates a secondary ray towards the light source, and checks if it is blocked by any other objects. If the secondary ray is blocked, the pixel is in shadow. Ray tracing is realistic and versatile, but it also has some drawbacks, such as high computational cost, noise, and aliasing.

4 Ambient Occlusion

Ambient occlusion is a technique for creating shadows that approximates the global illumination effects of the scene. It works by estimating how much each point in the scene is occluded by its surroundings, using a hemisphere of sample rays. Then, it modulates the ambient lighting of each point by its occlusion factor. Ambient occlusion is subtle and natural, but it also has some drawbacks, such as low frequency, lack of directionality, and temporal instability.

5 Screen Space Shadows

Screen space shadows are a technique for creating shadows that operates on the final image, rather than on the geometry of the scene. It works by using information from the depth buffer, the normal buffer, and the light vector to compute the visibility of each pixel from the light source. Then, it applies a filter or a blur to smooth the edges and create soft shadows. Screen space shadows are fast and efficient, but they also have some drawbacks, such as limited range, missing details, and artifacts.

6 Here’s what else to consider

This is a space to share examples, stories, or insights that don’t fit into any of the previous sections. What else would you like to add?