TeslaRel410/emulator/PHASE3-PROGRESS.md

Phase 3 — Render Backend: Progress

Status (2026-07-03): Phase 3a complete — the render command stream is fully captured and decoded, and a captured DIVRGB frame has been reconstructed to pixels. First image ever produced from the Rel 4.10 VPX protocol without a real board.

That is flyk divrgb.scn — Division's SMPTE color-bar calibration scene — rendered entirely from the FIFO command stream captured by the emulated VPX board: geometry, connectivity, materials, camera, viewport and background all come from the wire, none from the scene files. divrgb-frame0.png is the same capture drawn with the actual frame-0 spline camera the app sent.

3a. Full FIFO capture

vpxlog.cpp now records every FIFO burst when VPX_FIFODUMP=<path> is set (records: 'VPXM' magic, u32 length, raw bytes; one record per burst between outputData tag writes). The capture used here: divrgb.fifodump (1297 messages) from divrgb.conf.

Tools:

• decode_fifodump.py <dump> [--hex N] [--action A] — action census + payload hexdumps.
• render_capture.py <dump> [-o out.png] [--frame N] [--eye x,y,z] — reconstructs the scene graph and software-renders the frame each draw_scene commits.

The Rel 4.10 wire protocol (established from this capture)

One burst per message: [action:4][payload], packetized at 508 bytes. The i860 image download itself rides the FIFO in this build (actions 18–20, VREND.MNG). The DPL3 vr_action enum holds for 0–23 but Rel 4.10 extends and re-purposes the tail:

action	meaning	payload
0	init	args string (/device~0x150~/video~svga~…)
1	create	[type][name] — the host assigns node names (1,2,3…); the board's create reply node value is ignored
3	flush	[name][type][node struct] (see node types below)
7	dcs_link	[parent][child]
9	draw_scene	[view?][0][0][1][1.0f] — commits the frame
11	list_add	[parent][child]
18–21	860code/data/bss/args	i860 download (FIFO in this build)
23	set_geom_verts (Rel4.10; DPL3 had 22)	hdr [name][0][n_verts][3][n_blocks][1][5][n_verts][1.0f], then float32 x,y,z per vertex
25	set_geom_conns (new)	hdr [name][n_polys][loop_len][0], then indices; each poly a closed loop (last=first)
31	camera (new)	[?][view][3×3 rotation, row-major][eye x,y,z] per frame
45 (0x2D)	sync	token ping (see PHASE2)

Node types (from create/flush pairs in this capture):

type	node	flush payload highlights
2	texture/ramp?	one word, 0xFFFFFFFF / 0x0FFFFFFF
3	view	window l,b,r,t (±1 × ±0.6154), window-plane distance 1.3, viewport 832×512, near 2, far 12000, background RGB
4	light
5	dcs	4×4 matrix
6	material (old-style)	RGB floats
7	object
8	lod	2×4 bounds + lists
9	geogroup	bounds; payload int 14 = material node name
10	geometry	[geo_type][n_polys][n_verts]…[radius]
11	material	floats 10–12 (payload) = diffuse RGB

Graph: list_add links object→lod→geogroup→geometry (and zone-level nodes to node 0); geogroups bind materials by name. The 13 DIVRGB bars decode to the textbook SMPTE pattern — 7 color bars, the reverse strip, and the −I/white/+Q PLUGE row — which validates vertices, connectivity, materials, camera and window mapping in one image. (Division screen x runs opposite to a GL-style eye space; without negating x the pattern comes out mirrored.)

Next: 3b — live OpenGL backend

Feed the same decode path a live stream inside DOSBox-X instead of a dump: maintain the node store in vpxlog.cpp (or a sibling vpxrender.cpp), upload geometry on set_geom_verts/conns, draw on draw_scene into an OpenGL window (or the DOSBox surface). The divrgb.fifodump fixture allows developing the backend offline; flyk yip.scn (CYCLE, Red Planet geometry) is the next fixture up once the DOS/4GW sync variant is handled, then the game itself (buttee.bgf etc. via the production content path).