From 306be59cdea49c5d96aa6ede598b9e15353f8819 Mon Sep 17 00:00:00 2001
From: Gwilym Inzani <email@gwilym.dev>
Date: Tue, 27 Jun 2023 21:31:06 +0100
Subject: [PATCH] Add implementation for if this is the first

---
 agb/src/sound/mixer/mixer.s     | 17 +++++++++++++++--
 agb/src/sound/mixer/sw_mixer.rs |  8 +++++++-
 2 files changed, 22 insertions(+), 3 deletions(-)

diff --git a/agb/src/sound/mixer/mixer.s b/agb/src/sound/mixer/mixer.s
index 2299a22b..4fb974c8 100644
--- a/agb/src/sound/mixer/mixer.s
+++ b/agb/src/sound/mixer/mixer.s
@@ -91,7 +91,8 @@ same_modification:
 
 agb_arm_end agb_rs__mixer_add
 
-agb_arm_func agb_rs__mixer_add_stereo
+.macro stereo_add_fn fn_name:req is_first:req
+agb_arm_func \fn_name
     @ Arguments
     @ r0 - pointer to the data to be copied (u8 array)
     @ r1 - pointer to the sound buffer (i16 array which will alternate left and right channels, 32-bit aligned)
@@ -127,16 +128,24 @@ agb_arm_func agb_rs__mixer_add_stereo
     lsl r6, r6, #24        @ r6 = | R | 0 | 0 | 0 | drop everything except the right sample
     orr r6, r7, r6, asr #8 @ r6 = | 1 | R | 1 | L | now we have it perfectly set up
 
+.ifc \is_first,true
+    mul \sample_reg, r6, r2
+.else
     mla \sample_reg, r6, r2, \sample_reg     @ r4 += r6 * r2 (calculating both the left and right samples together)
+.endif
 .endm
 
 1:
+.ifc \is_first,true
+.else
     ldmia r1, {{r9-r12}}       @ read the current values
+.endif
 
     add_stereo_sample r9
     add_stereo_sample r10
     add_stereo_sample r11
     add_stereo_sample r12
+.purgem add_stereo_sample
 
     stmia r1!, {{r9-r12}}         @ store the new value, and increment the pointer
 
@@ -146,7 +155,11 @@ agb_arm_func agb_rs__mixer_add_stereo
     pop {{r4-r11}}
     bx lr
 
-agb_arm_end agb_rs__mixer_add_stereo
+agb_arm_end \fn_name
+.endm
+
+stereo_add_fn agb_rs__mixer_add_stereo false
+stereo_add_fn agb_rs__mixer_add_stereo_first true
 
 agb_arm_func agb_rs__mixer_collapse
     @ Arguments:
diff --git a/agb/src/sound/mixer/sw_mixer.rs b/agb/src/sound/mixer/sw_mixer.rs
index 387c67fb..efa4ce23 100644
--- a/agb/src/sound/mixer/sw_mixer.rs
+++ b/agb/src/sound/mixer/sw_mixer.rs
@@ -35,6 +35,12 @@ extern "C" {
         volume: Num<i16, 4>,
     );
 
+    fn agb_rs__mixer_add_stereo_first(
+        sound_data: *const u8,
+        sound_buffer: *mut Num<i16, 4>,
+        volume: Num<i16, 4>,
+    );
+
     fn agb_rs__mixer_collapse(
         sound_buffer: *mut i8,
         input_buffer: *const Num<i16, 4>,
@@ -406,7 +412,7 @@ impl MixerBuffer {
         working_buffer: &mut [Num<i16, 4>],
         channels: impl Iterator<Item = &'a mut SoundChannel>,
     ) {
-        working_buffer.fill(0.into());
+        // working_buffer.fill(0.into());
 
         for channel in channels {
             if channel.is_done {