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Understanding 3D rendering step by step with 3DMark11
by Damien Triolet
Published on January 27, 2012

Stage 7: secondary lights
To simulate global illumination, 3DMark 11 also calls on numerous secondary point lights. They represent a point which sends light in all directions. In the 3DMark 11 implementation, these are fill lights which ‘fill’ the light space and are thus part of the simulation effects taken into account for global illumination. More specifically, each of these light sources slightly illuminates the area it covers (a cube):



There are no fewer than 84 of these point lights in our test scene:


[ Directional lights ] + [ Fill lights ]

The point lights don’t generate any shadow as ambient occlusion simulates them at a lower processing cost. 3DMark 11 processes them in 2 passes to take into account a special case : when their volume of influence intersects the camera near plane.

Volumetric lighting can be computed for fill lights as well but it is not the case in our test scene.

Given the number of point lights, this part of the process represents a significant component of the rendering time.

A few stats:

Rendering times: 33.7 ms (26.8 %)
Vertices before tessellation: 688
Vertices after tessellation: -
Primitives: 1008
Primitives ejected from the rendering: 853
Pixels: 45.87 million
Elements exported by the pixel shaders: 45.87 million
Texels: 369.86 million
Instructions executed: 9073.06 million
Quantity of data read: 1494.2 MB
Quantity of data written: 177.6 MB

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