====== Parameterized Draw ======

Parameterized draw iterates one to five pairs of parameters. [[registers:risc-special:risc_40|DrawCtl]] selects the parameter assigned to each operand position. Its low nibble must differ from ''0xB''.

^ Pairs ^ Single instruction ^ Repeated instruction ^ Alignment of D, S2, S1 ^
| 1 | ''draw1 / F0'' | ''rdraw1 / F1'' | Double-word |
| 2 | ''draw2 / F2'' | ''rdraw2 / F3'' | Quad-word |
| 3 | ''draw3 / F8'' | ''rdraw3 / F9'' | Eight-word |
| 4 | ''draw4 / FA'' | ''rdraw4 / FB'' | Eight-word |
| 5 | ''draw5 / FC'' | ''rdraw5 / FD'' | Sixteen-word |

S2 contains starting parameters and S1 contains the corresponding deltas at the same offsets. DrawCtl pair fields select E1/O1 through E4/O4. The fifth pair is always G/B. A field marked ''*'' updates its register-file destination but is not used by the Pixel Engine.

Count is signed. When Count ≤ 0, no drawing occurs and Count is unchanged. For a single ''draw'', parameter destination registers receive the corresponding ''addv'' result only if Count > 0. ''rdraw'' does not modify the register-file destinations. The RISC stalls until an ''rdraw'' completes.

Leave one instruction after setting Count and three after setting DrawCtl. Updating XShadow has no hazard before a parameterized draw. If Fill is busy, parameterized drawing waits for it to finish.

===== Perspective and colors =====

Including Q performs UQ/Q and VQ/Q division per pixel. Perspective-correct forms require at least two pairs, and ''step q'' must precede the draw. Q is one pixel ahead of the other parameters.

R, G and B must be iterated together or all omitted. Intensity I supplies a common color value. Set SwapUV before setting U or V.

===== Timing note =====

The source gives repeated-draw timing as ''2 + 2 × ParamPairs + pixels'' cycles. It also says a single draw takes three cycles, then gives ''draw3'' launch as eight cycles (''2 + 2 × 3''). These statements conflict; [[reference:source_issues|DRAW_TIMING]] retains both. They are not combined into one assumed timing rule.

Sources: [[https://verite.3d32.org/_media/source/v2200spec.pdf#page=13|Technical Spec, p.13]], [[https://verite.3d32.org/_media/source/v2200spec.pdf#page=14|Technical Spec, p.14]], [[https://verite.3d32.org/_media/source/v2200spec.pdf#page=15|Technical Spec, p.15]]