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

Stage 6: primary lights
After preparing the data required for the creation of shadows, 3DMark 11 moves on to the rendering of the primary light sources, which take the shadows into account. These sources of light may be directional (sun, moon…) or spot type. There are no spot sources in the scene observed here but there is light from the sun. Five cascade shadow maps are required for the shadows generated by the sun across the scene. Calculation of these shadow maps is interleaved with the rendering of the lighting in the area of the field of view they cover so that they don’t monopolise the video memory too much.

This means that 3DMark 11 requires five passes to compute the directional lighting to simulate light from the sun (LD2a/b/c/d/e). An additional pass is used to help simulate the global illumination and more particularly the light from the sun reflected by the ground, as this then itself becomes a low intensity source of directional light (LD1). Thus the light accumulates little by little in the image under preparation:

[ Sky ] + [ LD 1 ] + [ LD2a ] + [ LD2b ] + [ LD2c ] + [ LD2d ] + [ LD2e ]

This image under preparation, in R11G11B10_FLOAT (fast HDR 32-bit) format, represents surface lighting, the model for which is a combination of diffuse Oren-Nayar reflectance and Cook-Torrance specular reflectance as well as Rayleigh-Mie type atmospheric attenuation. In addition to the shadow maps, it takes into account the ambient occlusion calculated previously.

In parallel to the surface lighting, volumetric lighting is also calculated. See the page on this for further details. Its performance cost is however included in the figures given here as it’s processed in the same pixel shader as surface lighting.

A few stats:

Rendering times: 24.7 ms (19.6 %)
Vertices before tessellation: 18
Vertices after tessellation: -
Primitives: 6
Primitives ejected from the rendering: 0
Pixels: 8.13 million
Elements exported by pixel shaders: 14.18 million
Texels: 390.91 million
Instructions executed: 2567.59 million
Quantity of data read: 1979.2 MB
Quantity of data written: 54.6 MB

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Stage 7: secondary lights  

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