feat: replace DSSound slot 5 (set_pan) with Rust

Pan uses the same VOLUME_DB_TABLE read backwards — index 0 from the end
gives near-0 dB (no attenuation), larger indices give more attenuation.
Positive pan negates the dB value for right-channel bias.

20/24 DSSound vtable slots now Rust.

Co-Authored-By: Claude Opus 4.6 (1M context) <noreply@anthropic.com>

crates/openwa-core/src/audio/dssound.rs

@@ -287,6 +287,42 @@ pub unsafe extern "thiscall" fn set_master_volume(
     1
 }
 
+/// Slot 5: set_pan — sets stereo panning on a specific channel.
+/// `pool_id` is 1-based (1..64). `pan` is Fixed 16.16 (-0x10000..0x10000).
+/// Negative = left, positive = right.
+pub unsafe extern "thiscall" fn set_pan(
+    this: *mut DSSound, pool_id: i32, pan: i32,
+) -> u32 {
+    let idx = (pool_id - 1) as usize;
+    if idx >= 64 {
+        return 0;
+    }
+    let snd = &*this;
+    let desc_idx = snd.buffer_pool_shadow[idx];
+    if desc_idx < 0 || desc_idx as usize >= 8 {
+        return 0;
+    }
+
+    // Clamp pan to [-0x10000, 0x10000].
+    let pan = pan.max(-0x10000).min(0x10000);
+
+    // Index into table backwards: abs(pan) >> 10 gives 0..63.
+    // Table is read from the END (index 63 = near silence, index 0 = full).
+    let table_idx = ((pan.unsigned_abs() >> 10) as usize).min(63);
+    let mut db = VOLUME_DB_TABLE[63 - table_idx] as i32;
+
+    // Positive pan → negate (right channel louder = negative pan dB for left).
+    if pan > 0 {
+        db = -db;
+    }
+
+    if let Some(buf) = snd.channel_descs[desc_idx as usize].buffer() {
+        let _ = buf.SetPan(db);
+    }
+
+    1
+}
+
 /// Slot 8: set_channel_volume — sets volume on a specific channel.
 /// `pool_id` is 1-based (1..64). `volume` is Fixed 16.16 (0..0x10000).
 pub unsafe extern "thiscall" fn set_channel_volume(

crates/openwa-core/src/audio/mod.rs

@@ -10,7 +10,7 @@ pub use dssound::{DSSound, DSSoundVtable, ChannelDescriptor};
 pub use dssound::{
     update_channels, release_finished,
     is_slot_loaded, is_channel_finished, stop_channel,
-    set_master_volume, set_channel_volume,
+    set_master_volume, set_channel_volume, set_pan,
     sub_destructor as dssound_sub_destructor, load_wav,
     noop as dssound_noop, returns_0 as dssound_returns_0, returns_1 as dssound_returns_1,
 };

crates/openwa-wormkit/src/replacements/sound.rs

@@ -170,7 +170,7 @@ unsafe fn patch_dssound_vtable() -> Result<(), String> {
     use openwa_core::audio::{
         update_channels, release_finished,
         is_slot_loaded, is_channel_finished, stop_channel,
-        set_master_volume, set_channel_volume, dssound_sub_destructor,
+        set_master_volume, set_channel_volume, set_pan, dssound_sub_destructor,
         load_wav, dssound_noop, dssound_returns_0, dssound_returns_1,
     };
 
@@ -192,6 +192,9 @@ unsafe fn patch_dssound_vtable() -> Result<(), String> {
         // Slot 11: release_finished — like update_channels, returns count
         *vt.add(11) = release_finished as *const () as u32;
 
+        // Slot 5: set_pan — stereo panning with dB lookup
+        *vt.add(5) = set_pan as *const () as u32;
+
         // Slot 9: is_channel_finished — returns 0 if playing, 1 if stopped/free
         *vt.add(9) = is_channel_finished as *const () as u32;
 
@@ -216,6 +219,6 @@ unsafe fn patch_dssound_vtable() -> Result<(), String> {
         // Trivial returns-1 (slot 23)
         *vt.add(23) = dssound_returns_1 as *const () as u32;
 
-        let _ = log_line("[Sound]   DSSound vtable: patched 19/24 slots with Rust");
+        let _ = log_line("[Sound]   DSSound vtable: patched 20/24 slots with Rust");
     }).map_err(|e| e.to_string())
 }