110
edits
Changes
→Geometry Pipeline: Added section about immediate mode
To specify the actual value of the fixed attribute, write the attribute index to [[GPU:Internal Registers#GPUREG_FIXEDATTRIB_INDEX|GPUREG_FIXEDATTRIB_INDEX]] followed by writes with packed a float24 4-tuple to the 3 [[GPU:Internal Registers#GPUREG_FIXEDATTRIB_DATA|GPUREG_FIXEDATTRIB_DATA]] registers. The value is always specified as a float 4-component vector, the configured type is ignored.
To specify the actual value of the fixed attribute, write the attribute index to [[GPU:Internal Registers#GPUREG_FIXEDATTRIB_INDEX|GPUREG_FIXEDATTRIB_INDEX]] followed by writes with packed a float24 4-tuple to the 3 [[GPU:Internal Registers#GPUREG_FIXEDATTRIB_DATA|GPUREG_FIXEDATTRIB_DATA]] registers. The value is always specified as a float 4-component vector, the configured type is ignored.
== Immediate-Mode Vertex Submission ==
Instead of using vertex arrays to supply vertex data, drawing can be done by directly writing vertex data to a register. This allows vertex data to be inlined directly in the command buffer. Since this is restricted to 4-component float data, it is more useful for small draws like UI elements or debug displays, to avoid using an unreasonable amount of memory and processing time appending the vertices to the command buffer.
To use this feature, configure the number of attributes per vertex in [[GPU:Internal Registers#GPUREG_ATTRIBBUFFERS_FORMAT_HIGH|GPUREG_ATTRIBBUFFERS_FORMAT_HIGH]]. (All other settings in related registers seem to be ignored.) Then setup the GPU the same as if doing a regular draw call with GPUREG_DRAWARRAYS or GPUREG_DRAWELEMENTS, but instead of writing to either register, write the value 0xF to [[GPU:Internal Registers#GPUREG_FIXEDATTRIB_INDEX|GPUREG_FIXEDATTRIB_INDEX]] and then follow by repeatedly writing vertex data to [[GPU:Internal Registers#GPUREG_FIXEDATTRIB_DATA|GPUREG_FIXEDATTRIB_DATA]].
Each set of writes to the 3 data registers specifies one attribute and all attributes (as configured in GPUREG_ATTRIBBUFFERS_FORMAT_HIGH) need to be written, in order, to specify a vertex. Drawing happens automatically as vertices are specified. After finishing specifying vertices, follow with the same writes used after a draw arrays/elements.
When drawing using triangle strips or fans, [[GPU:Internal Registers#GPUREG_RESTART_PRIMITIVE|GPUREG_RESTART_PRIMITIVE]] should be used to end the previous strip before (or while) drawing.