6.2 Predefined Shader Variables

For each shader, some predefined variables are provided for input and output purposes. Here are the lists of variables for each shader type. Variables with a `*' at the end of their description are available only inside illuminance constructs (see The Illuminance Construct) .

6.2.1 Predefined Surface Shader Variables
6.2.2 Predefined Light Shader Variables
6.2.3 Predefined Volume Shader Variables
6.2.4 Predefined Displacement Shader Variables
6.2.5 Predefined Imager Shader Variables

6.2.1 Predefined Surface Shader Variables

Table 6.5: Predefined Surface Shader Variables.

Name Type Storage Description Cs color varying Surface color. Os color varying Surface opacity. P point varying Surface position. dPdu vector varying Derivative of surface position along u. dPdv vector varying Derivative of surface position along v. N normal varying Surface shading normal. Ng normal varying Surface geometric normal. u, v float varying Surface parameters. du, dv float varying Change of surface parameters. s, t float varying Surface texture coordinates. E point uniform Position of the eye. I vector varying Incident ray direction. ncomps float uniform Number of color components. time float uniform Current shutter time, as specified by RiShutter. dtime float uniform The amount of time covered by this shading sample. dPdtime vector varying How the surface position P is changing per unit time, as described by motion blur in the scene. Ci color varying Same as Cs. Oi color varying Same as Os. L vector varying Incoming light ray direction. * Cl color varying Incoming light ray color. * Ol color varying Incoming light ray opacity. * Output Ci color varying Incident ray color. Oi color varying Incident ray opacity. P point varying Displaced surface position. N vector varying Displaced surface shading normal.

6.2.2 Predefined Light Shader Variables

Table 6.6: Predefined Light source Variables

Name Type Storage Description P point varying Surface position on the light. dPdu vector varying Derivative of surface position along u. dPdv vector varying Derivative of surface position along v. N normal varying Surface shading normal on the light. Ng normal varying Surface geometric normal on the light. u, v float varying Surface parameters. du, dv float varying Change of surface parameters. s, t float varying Surface texture coordinates. L vector varying Outgoing light ray direction. * Ps point varying Position being illuminated. E point uniform Position of the eye. ncomps float uniform Number of color components. time float uniform Current shutter time, as specified by RiShutter. dtime float uniform The amount of time covered by this shading sample. I vector varying Incident ray direction. * Output Cl color varying Outgoing light ray color. Ol color varying Outgoing light ray opacity.

6.2.3 Predefined Volume Shader Variables

Table 6.7: Predefined Volume Shader Variables

Name Type Storage Description P point varying Light ray endpoint. I vector varying Ray direction (pointing toward P). E point uniform Position of the eye. Ci color varying Ray color. Oi color varying Ray opacity. ncomps float uniform Number of color components. time float uniform Current shutter time, as specified by RiShutter. dtime float uniform The amount of time covered by this shading sample. dPdu vector varying Derivative of surface position along u. dPdv vector varying Derivative of surface position along v. N normal varying Surface shading normal. Ng normal varying Surface geometric normal. u, v float varying Surface parameters. du, dv float varying Change of surface parameters. s, t float varying Surface texture coordinates. Cs color varying Same as Ci. Os color varying Same as Oi. Output Ci color varying Attenuated ray color. Oi color varying Attenuated ray opacity.

6.2.4 Predefined Displacement Shader Variables

Table 6.8: Predefined Displacement Shader Variables

Name Type Storage Description P point varying Surface position. dPdu vector varying Derivative of surface position along u. dPdv vector varying Derivative of surface position along v. N normal varying Surface shading normal. Ng normal varying Surface geometric normal. I vector varying Incident ray direction. E point uniform Position of the eye. u, v float varying Surface parameters. du, dv float varying Change of surface parameters. s, t float varying Surface texture coordinates. ncomps float uniform Number of color components. time float uniform Current shutter time, as specified by RiShutter. dtime float uniform The amount of time covered by this shading sample. dPdtime vector varying How the surface position P is changing per unit time, as described by motionblur in the scene. Output P point varying Displaced surface position. N normal varying Displaced surface shading normal.

6.2.5 Predefined Imager Shader Variables

Table 6.9: Predefined Imager Shader Variables

Name Type Storage Description P point varying Pixel raster position. Ci color varying Pixel color. Oi color varying Pixel opacity. u, v float varying Surface parameters. Set to pixel's raster coordinates. s, t float varying Surface texture coordinate. Set to pixel's raster coordinates. du, dv float varying Change of surface parameters. (du = 1.0 / x resolution, dv = 1.0f / y resolution ). alpha float uniform Fractional pixel coverage. ncomps float uniform Number of color components. time float uniform Shutter open time. dtime float uniform The amount of time the shutter was open. Output Ci color varying Output pixel color. Oi color varying Output pixel opacity. alpha float uniform Output pixel coverage.

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