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How does a shadow map work?
Shadow mapping or shadowing projection is a process by which shadows are added to 3D computer graphics. Shadows are created by testing whether a pixel is visible from the light source, by comparing the pixel to a z-buffer or depth image of the light source’s view, stored in the form of a texture.
Why is the length of shadow smallest at noon?
As the Sun moves, light falls on the object at an angle. The bigger angle, the longer the shadow. At noon, the Sun is directly overhead. This makes the smallest angle with the objects and so creates the shortest shadows.
Why does the length of the shadow change over the day?
The Sun’s position in the sky affects the length of the shadow. When the Sun is low on the horizon, the shadows are long. When the Sun is high in the sky, the shadows are much shorter. Due to the Earth’s rotation, our view of the Sun changes throughout the day.
Can a cascade be rendered as a shadow map?
Every cascade will be rendered into its own private shadow map. The shadow algorithm itself will remain the same but when sampling the depth from the shadow map we will need to select the appropriate map based on the distance from the viewer. Let’s take a look at a generic view frustum: As usual, we have a small near plane and a larger far plane.
How does a light space perspective shadow map work?
Light Space Perspective Shadow Maps (LiPSM) [4] wrap the camera frustum in a way that doesn’t change the directions of light sources. A new light frustum is built that has a viewing ray perpendicular to the light’s direction (parallel to the shadow map).
Which is the best shadow map to use?
The shadow map with the most closely placed pixels (at the apex) is nearest the eye. Technically, these are maps of the same size, with white and grey used to exemplify the success of the cascaded shadow map. White is ideal because it shows good coverage—a 1:1 ratio for eye-space pixels and shadow-map texels.
How is pixel coverage affected by shadow maps?
The series of grids representing shadow maps with a view frustum (inverted cone in red) shows how pixel coverage is affected with different resolution shadow maps. Shadows are of the highest quality (white pixels) when there is a 1:1 ratio mapping pixels in light space to texels in the shadow map.