From bf4246f236a8c272e898d05c4c41bbb6f692c573 Mon Sep 17 00:00:00 2001
From: Matthew Stanley <1379tech@gmail.com>
Date: Thu, 8 Oct 2026 05:49:27 -0700
Subject: [PATCH] Share newly exposed placement bounds for adaptive scene
 residency

---
 runtime/include/mod_visible_placements.h | 26 ++++++++++++++++++++++++
 runtime/tests/test_mod_capcom_bg2d.c     | 14 +++++++++++++
 2 files changed, 40 insertions(+)
 create mode 100644 runtime/include/mod_visible_placements.h

diff --git a/runtime/include/mod_visible_placements.h b/runtime/include/mod_visible_placements.h
new file mode 100644
index 00000000..241fbf7a
--- /dev/null
+++ b/runtime/include/mod_visible_placements.h
@@ -0,0 +1,26 @@
+#ifndef PSXRECOMP_MOD_VISIBLE_PLACEMENTS_H
+#define PSXRECOMP_MOD_VISIBLE_PLACEMENTS_H
+#include <stdint.h>
+
+/* Authored placement visibility, independent of a title's actor allocator.
+ * Rectangles use the strict bounds of the original Capcom placement scan.
+ * Caller stores its visited bitmap/previous rectangle in snapshotted mod RAM. */
+typedef struct PSXPlacementRect { int32_t left,right,top,bottom; } PSXPlacementRect;
+static inline int psx_placement_contains(PSXPlacementRect r,int32_t x,int32_t y) {
+    return x>r.left && x<r.right && y>r.top && y<r.bottom;
+}
+/* Return only newly exposed strips. Overlapping edge coordinates are included
+ * in the strip bounds because the original scanner excludes its endpoints. */
+static inline unsigned psx_placement_exposed(PSXPlacementRect old,PSXPlacementRect now,
+                                            int valid,PSXPlacementRect out[4]) {
+    if (!valid || now.left>=old.right || now.right<=old.left ||
+        now.top>=old.bottom || now.bottom<=old.top) { out[0]=now;return 1; }
+    unsigned n=0;
+    if(now.left<old.left)out[n++]=(PSXPlacementRect){now.left,old.left+1,now.top,now.bottom};
+    if(now.right>old.right)out[n++]=(PSXPlacementRect){old.right-1,now.right,now.top,now.bottom};
+    int32_t left=now.left>old.left?now.left:old.left,right=now.right<old.right?now.right:old.right;
+    if(now.top<old.top)out[n++]=(PSXPlacementRect){left,right,now.top,old.top+1};
+    if(now.bottom>old.bottom)out[n++]=(PSXPlacementRect){left,right,old.bottom-1,now.bottom};
+    return n;
+}
+#endif
diff --git a/runtime/tests/test_mod_capcom_bg2d.c b/runtime/tests/test_mod_capcom_bg2d.c
index 3e0a993f..d98a44a9 100644
--- a/runtime/tests/test_mod_capcom_bg2d.c
+++ b/runtime/tests/test_mod_capcom_bg2d.c
@@ -5,6 +5,7 @@
 #include <stdio.h>
 #include <string.h>
 #include "mod_capcom_bg2d.h"
+#include "mod_visible_placements.h"
 
 static unsigned char memory[10u * 1024u * 1024u];
 static uint32_t writes;
@@ -28,6 +29,19 @@ void gpu_ws_bg2d_set_host_arena(uint32_t base, uint32_t bytes) {
 }
 
 int main(void) {
+    PSXPlacementRect original={0,320,0,240},wide={-160,480,0,240},strips[4];
+    assert(psx_placement_exposed(original,wide,0,strips)==1);
+    assert(psx_placement_exposed(wide,wide,1,strips)==0); /* No repeat scan while idle. */
+    assert(psx_placement_exposed(original,wide,1,strips)==2);
+    assert(psx_placement_contains(strips[0],-100,100));
+    assert(psx_placement_contains(strips[1],400,100));
+    assert(!psx_placement_contains(strips[1],319,100));
+    PSXPlacementRect moved={-128,512,0,240};
+    assert(psx_placement_exposed(wide,moved,1,strips)==1);
+    assert(psx_placement_contains(strips[0],500,100));
+    assert(!psx_placement_contains(strips[0],400,100)); /* A killed wide enemy is not revisited. */
+    assert(psx_placement_contains(wide,400,100));
+    assert(!psx_placement_contains((PSXPlacementRect){480,1120,0,240},400,100));
     WsViewAnchor centered = {106,106,0,0,0};
     WsViewAnchor mapped = psx_capcom_scroll_view(centered,800,667);
     assert(mapped.left==133 && mapped.right==79 && mapped.shift==27);