From 12d2952e9fd6cc0015c7e607ffecbd4b5395ec36 Mon Sep 17 00:00:00 2001
From: Cyd <cyd@falloutshelterarcade.com>
Date: Fri, 3 Jul 2026 20:31:51 -0500
Subject: [PATCH] VDB: palette-reload delta probe (test palette-animation
 hypothesis)

On each palette reload, diff against the previous captured palette and log how
many of the 256 entries changed plus the first few index:old->new. Confirms
the static/dynamic split: pal1/pal2 load once (static base structure -- red in
odd entries, etc.), pal0 is rewritten ~28x. In this capture pal0 is doing the
intro FadeToWhite -- ~216/256 entries ramping in lockstep from 0 to ~60/63 --
i.e. animating the whole display brightness via the palette without redrawing
the framebuffer. Selective per-element flashing (targeted small deltas) would
need an active mission to observe; this probe is the instrument for it.

Co-Authored-By: Claude Opus 4.8 <noreply@anthropic.com>
---
 emulator/vpx-device/vpxlog.cpp | 31 +++++++++++++++++++++++++++++--
 1 file changed, 29 insertions(+), 2 deletions(-)

diff --git a/emulator/vpx-device/vpxlog.cpp b/emulator/vpx-device/vpxlog.cpp
index 983b48f..001968d 100644
--- a/emulator/vpx-device/vpxlog.cpp
+++ b/emulator/vpx-device/vpxlog.cpp
@@ -1197,9 +1197,36 @@ static int vdb_group_base(int g) { return 2 + 8 * g; }
 static void vdb_flush_data(void) {
     if (vdb_data_group >= 0 && vdb_data_count) {
         if (vpx_fp) {
+            /* Palette-animation probe: on each reload, diff against the last
+             * captured palette for this group and report how many of the 256
+             * entries changed (+ the first few index:old->new), so the
+             * "flashed" data can be seen. */
+            static unsigned char prev[3][768];
+            static bool have_prev[3] = { false, false, false };
+            int g = vdb_data_group;
             flush_run();
-            fprintf(vpx_fp, "# VDB pal%d loaded %lu data bytes\n",
-                    vdb_data_group, vdb_data_count);
+            if (have_prev[g]) {
+                int changed = 0, first[4], nf = 0;
+                for (int i = 0; i < 256; i++) {
+                    if (memcmp(&vdb_pal[g].ram[i*3], &prev[g][i*3], 3) != 0) {
+                        if (nf < 4) first[nf++] = i;
+                        changed++;
+                    }
+                }
+                fprintf(vpx_fp, "# VDB pal%d reload: %d/256 entries changed", g, changed);
+                for (int k = 0; k < nf; k++) {
+                    int i = first[k];
+                    fprintf(vpx_fp, "  [%d]%d,%d,%d->%d,%d,%d", i,
+                            prev[g][i*3], prev[g][i*3+1], prev[g][i*3+2],
+                            vdb_pal[g].ram[i*3], vdb_pal[g].ram[i*3+1], vdb_pal[g].ram[i*3+2]);
+                }
+                fprintf(vpx_fp, "\n");
+            } else {
+                fprintf(vpx_fp, "# VDB pal%d loaded %lu data bytes (first)\n",
+                        g, vdb_data_count);
+            }
+            memcpy(prev[g], vdb_pal[g].ram, 768);
+            have_prev[g] = true;
             fflush(vpx_fp);
         }
         if (vdb_paldump && vdb_data_count >= 768) {