Shader: "shadow catcher"

"shadow catcher"

Synopsis Allows shadows to fall upon hidden geometry in a scene. Usually the supplied geometry will follow some detail depicted by a background image. This then allows objects that have been placed in the scene to cast shadows that appear to interact with the background in a natural way.

"catch" Description: Three settings for the way in which shadows are analysed are provided; "none", specifies that shadow analysis is not performed but the shadow catcher primitive is shaded directly with the background followed by execution of any specified reflectance shader; "all" is the same but with shadow analysis (in this mode shadows are cast by the scene geometry and the absence of light is considered as total shadow--- so for example a region outside a spot light cone is determined to be in total shadow); "shadows only" specifies that shadow analysis is performed as described above but in this mode only a shadow created by geometry is considered to be a true shadow.
"shadow colour" Description: Specifies a filter colour to be applied to the shadow. Use this parameter to tint a shadow a desired colour, for example to match the ambient lighting conditions. Note that if any ambient lights are illuminating the scene then they only affect the shadowed area and not the shadow catcher geometry as a whole. The effects of ambient lighting are added to the shadow region before any filtering by shadow colour is performed. Any ambient lighting contributions to the shadow region are also clamped to ensure that this region is never brighter than its surroundings.
Default:1.0, 1.0, 1.0
Hint: [ 0, 1 ], [ 0, 1 ], [ 0, 1 ]
"shadow brightness" Description: Limits the darkest value that a shadow can be, where 0.0 is total shadow (i.e., black) and 1.0 is total illumination. This threshold value is applied as a limiting value to the total shadow at a point. The total shadow is the sum of the individual shadow contributions from each light source.
Hint:[ 0.2, 0.8 ]
"reflectance" Description: A reflectance class shader that may be used as input to the shader to provide the geometry with the reflectance properties that match the scenery it represents. For example, a reflectance shader may be used so that background covered by a shadow catcher responds to the lighting conditions in a natural way.
"light types" Description: This parameter specifies which light types will be considered by the shadow catcher when calculating the shadow coverage at each point. By default, all valid light types are considered. Any light type which is not included in this bitfield will not illuminate or cast a shadow onto the shadow catcher.

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