render3d: stream_capture runs the game's own fill for a chunk outside any frame, for the bake

stream_capture(s, cx, cz, band) points the stream at a chunk of its own (made on the first capture),
calls the registered r3d_stream_fill for that cell and band, and returns how many instances it
emitted; stream_captured(i, k) reads them from stream_scratch. Build-time only; nothing in a frame
calls it.

Co-Authored-By: Claude Opus 5.5 <noreply@anthropic.com>

packages/ludic.render3d/env.ludic

@@ -829,6 +829,7 @@ export state Render3dState {
   ter_ortho_tex: int = 0            # a photograph of the same window, draped with distance
   ter_carpet: int = 0               # the distant-grass carpet (carpet_bake), 0 = none
   ter_shadow_tex: int = 0           # height-field sun shadow: R32F, the lowest lit height
+  stream_capture_c: Chunk = null    # the bake's capture chunk (stream_baked.ludic)
   sb_rec: floats = floats(8)        # one decoded baked record, reused (stream_baked.ludic)
   tt_dir: string = ""               # terrain_tiles_to: where a map's tiles are written ("" keeps the whole copies)
   tt_key: string = ""

packages/ludic.render3d/stream_baked.ludic

@@ -25,3 +25,22 @@ export function stream_band_keep(count: int, share: float) -> int {
   if count == 0 { return 0 }
   return max(1, min(count, int(float(count) * share + 0.5)))
 }
+
+# ---- the bake's capture -----------------------------------------------------------------------
+# The game's own fill for chunk (cx, cz) at a band, run outside any frame into a chunk of its own: what
+# the bake records. The instances are left in stream_scratch (INST_FLOATS each: x, y, z, scale, sin yaw,
+# cos yaw, seed, wind; stream_captured reads them) and their count is returned. Build-time only.
+@alloc_ok("a bake's capture chunk, made on the first capture")
+export function stream_capture(render3d_st: mut Render3dState, s: Stream, cx: int, cz: int, band: int) -> int {
+  if render3d_st.stream_scratch == null { render3d_st.stream_scratch = floats(STREAM_CHUNK_MAX * INST_FLOATS) }
+  if render3d_st.stream_capture_c == null { render3d_st.stream_capture_c = new Chunk }
+  let c = render3d_st.stream_capture_c
+  c.key = stream_key(cx, cz, band);  c.count = 0;  c.off = -1;  c.used = 0
+  s.cur = c
+  r3d_stream_fill(render3d_st, s, cx, cz, band)
+  s.cur = null
+  return c.count
+}
+
+# field k (0 .. INST_FLOATS - 1) of captured instance i
+export function stream_captured(render3d_st: Render3dState, i: int, k: int) -> float { return render3d_st.stream_scratch[i * INST_FLOATS + k] }