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Add docs for Fixed Vertex Attribute registers
This register configures the geometry stage of the GPU pipeline.
This register configures the geometry stage of the GPU pipeline.
=== GPUREG_FIXEDATTRIB_INDEX ===
{| class="wikitable" border="1"
! Bits
! Description
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| 0-31
| Sets the active fixed attribute index. This is the fixed attribute which will be set when writing to [[#GPUREG_FIXEDATTRIB_DATA|GPUREG_FIXEDATTRIB_DATA]]. Valid values are 0-11. If the special value 0xF is written here, this sets up immediate-mode vertex submission instead, and writes to the data register will input vertex data directly into the pipeline.
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=== GPUREG_FIXEDATTRIB_DATA ===
Accepts a packed 4-tuple of float24 values (in the same format used for [[#GPUREG_VSH_FLOATUNIFORM_DATA|specifying shader uniforms]]). This is stored as the fixed attribute value for the attribute currently specified in the index register. Attributes are always specified as a 4-tuple of floats, regardless of the format configured in [[#GPUREG_ATTRIBBUFFERS_FORMAT_HIGH|GPUREG_ATTRIBBUFFERS_FORMAT_HIGH]].
If immediate-mode vertex submission is enabled (by writing 0xF to the index register) then vertex data is input here directly. The configured number N of vertex attributes (specified in [[#GPUREG_ATTRIBBUFFERS_FORMAT_HIGH|GPUREG_ATTRIBBUFFERS_FORMAT_HIGH]]) for each vertex should be sent in sequence. One vertex is output for every N 4-tuples written, and the index register does not need to be reset between attributes or vertices.
== Geometry shader registers ==
== Geometry shader registers ==