tools: separate 'submitted' from 'on screen' in a draw log

The blend map reports a quad's SIZE, which identifies an element and says nothing
about whether it is visible -- a parked quad is still a draw call. This prints
the NDC x/y range and per-vertex colour of every additive draw, per frame, so
movement between frames and overlap with the [-1,1] box are readable directly.

Written because sylpheed-port flagged exactly that conflation in my blend page:
the blend and the visibility arrived in the same artefact.

Co-Authored-By: Claude Opus 5 (1M context) <noreply@anthropic.com>
Claude-Session: https://claude.ai/code/session_01Wuu56cE8vJGTBtn1ppsk8v

tools/re-capture/sweep_positions.py

@@ -0,0 +1,52 @@
+#!/usr/bin/env python3
+"""Where the two rotated sweep strips actually are, per frame, from a draw log.
+
+    sweep_positions.py <xenia_re_ui_draws_NN.log> [...]
+
+The blend map reports a quad's SIZE. That identifies an element and says nothing
+about whether it is on screen: a parked quad is still a draw call. This prints the
+NDC x-range and the per-vertex colour of every 8-vertex ADDITIVE draw, per frame,
+so "submitted" and "visible" stop being the same observation.
+
+NDC x is in [-1, +1] across the surface, so a strip overlaps the screen iff
+x_min < 1 and x_max > -1. Movement between frames is the loop running.
+"""
+import re
+import sys
+
+VIS_LO, VIS_HI = -1.0, 1.0
+
+
+def quads(line):
+    vs = [(float(a), float(b), c) for a, b, c in
+          re.findall(r"\[(-?\d+\.\d+),(-?\d+\.\d+),z=[-\d.]+,col=([0-9A-F]{8})\]", line)]
+    return [vs[i:i + 4] for i in range(0, len(vs) - 3, 4)]
+
+
+def main():
+    for path in sys.argv[1:]:
+        print("=== %s ===" % path)
+        lines = open(path).read().splitlines()
+        frame = 0
+        print("%-6s %-5s %-6s  %-18s %-18s %-8s %s"
+              % ("frame", "draw", "quad", "NDC x range", "NDC y range", "col", "on screen?"))
+        for i, line in enumerate(lines):
+            m = re.match(r"--- frame (\d+) ---", line)
+            if m:
+                frame = int(m.group(1))
+                continue
+            m = re.search(r"^\s*(\d+) prim=\d+ indices=(\d+).* blend=0x01010101", line)
+            if not m or i + 1 >= len(lines):
+                continue
+            for k, q in enumerate(quads(lines[i + 1])):
+                xs = [p[0] for p in q]
+                ys = [p[1] for p in q]
+                on = min(xs) < VIS_HI and max(xs) > VIS_LO and min(ys) < VIS_HI and max(ys) > VIS_LO
+                print("%-6d %-5s %-6d  %7.2f .. %7.2f  %7.2f .. %7.2f  %-8s %s"
+                      % (frame, m.group(1), k, min(xs), max(xs), min(ys), max(ys),
+                         q[0][2], "ON SCREEN" if on else "parked off screen"))
+        print()
+
+
+if __name__ == "__main__":
+    main()