From 65089bc6ca9e31878afd583e133cb376ef03f268 Mon Sep 17 00:00:00 2001
From: Bad Diode <bd@badd10de.dev>
Date: Mon, 15 Jan 2024 14:50:21 +0100
Subject: [WIP] Initial implementation of CH3 envelope

---
 src/sequencer.c | 69 +++++++++++++++++++++++++++++++++++++++++++++++++--------
 1 file changed, 60 insertions(+), 9 deletions(-)

(limited to 'src/sequencer.c')

diff --git a/src/sequencer.c b/src/sequencer.c
index 981bbc6..01b8e95 100644
--- a/src/sequencer.c
+++ b/src/sequencer.c
@@ -229,14 +229,16 @@ play_step(void) {
         if (trig->active && should_play(params->prob)) {
             switch (params->wave_mode) {
                 case 0: {
+                    memcpy32(wave_active, waves[params->shape_a][params->type_a], 16);
                     SOUND_WAVE_MODE = SOUND_WAVE_BANK_SELECT(1);
-                    memcpy32(SOUND_WAVE_RAM, waves[params->shape_a][params->type_a], 16);
+                    memcpy32(SOUND_WAVE_RAM, wave_active, 16);
                     SOUND_WAVE_MODE = SOUND_WAVE_BANK_MODE(0)
                         | SOUND_WAVE_BANK_SELECT(0);
                 } break;
                 case 1: {
+                    memcpy32(wave_active, waves[params->shape_b][params->type_b], 16);
                     SOUND_WAVE_MODE = SOUND_WAVE_BANK_SELECT(0);
-                    memcpy32(SOUND_WAVE_RAM, waves[params->shape_b][params->type_b], 16);
+                    memcpy32(SOUND_WAVE_RAM, wave_active, 16);
                     SOUND_WAVE_MODE = SOUND_WAVE_BANK_MODE(0)
                         | SOUND_WAVE_BANK_SELECT(1);
                 } break;
@@ -249,6 +251,7 @@ play_step(void) {
                         | SOUND_WAVE_BANK_SELECT(0);
                 } break;
             }
+            wave_env_ticks = 0;
             SOUND_WAVE_MODE |= SOUND_WAVE_ENABLE;
 
             SOUND_WAVE_FREQ = SOUND_FREQ_RESET
@@ -261,12 +264,6 @@ play_step(void) {
                 case 4: { SOUND_WAVE_CTRL = SOUND_WAVE_VOL_100; } break;
             }
             pan[2] = params->pan;
-        } else {
-            // NOTE: Maybe in the future we want an AD, but for now this is
-            // probably better than holding the notes. Or perhaps add a hold
-            // mode?
-            SOUND_WAVE_FREQ = SOUND_FREQ_RESET;
-            SOUND_WAVE_CTRL = SOUND_WAVE_MUTE;
         }
     } else {
         SOUND_WAVE_FREQ = SOUND_FREQ_RESET;
@@ -352,11 +349,65 @@ play_step(void) {
 
 static int nseq_ticks = 0;
 
+IWRAM_CODE
+void
+wave_ad_tick(void) {
+    // Play a single step for A+B or no envelope.
+    if ((SOUND_WAVE_MODE & SOUND_WAVE_BANK_MODE(1)) || !wave_env_decay) {
+        if (wave_env_ticks++ == 24) {
+            SOUND_WAVE_FREQ = SOUND_FREQ_RESET;
+            SOUND_WAVE_CTRL = SOUND_WAVE_MUTE;
+        }
+        return;
+    }
+
+    if (wave_env_ticks++ < wave_env_decay) {
+        return;
+    }
+    wave_env_ticks = 0;
+
+    // Decay.
+    for (size_t j = 0; j < 4; j++) {
+        u32 next = 0;
+        for (size_t i = 0; i < 8; i++) {
+            u8 val = (wave_active[j] >> 4 * i) & 0xF;
+            // Operating in 24.8 fixed point:
+            // 0.9 = 230; 0.8 = 205; 0.75 = 192
+            int power = 205;
+            if (val < 0x7) {
+                int tmp = 0x7 - val;
+                tmp *= power;
+                tmp >>= 8;
+                val = (0x7 - tmp) & 0xf;
+            } else if (val > 0x7) {
+                int tmp = (val - 0x7);
+                tmp *= power;
+                tmp >>= 8;
+                val = tmp + 0x7;
+                if (val <= 0x7) {
+                    val = 0x7;
+                }
+            }
+            next |= (val << 4 * i);
+        }
+        wave_active[j] = next;
+    }
+
+    // DEBUG:
+    // int x = 50;
+    // int y = 50;
+    // draw_filled_rect(0 + x, 0 + y, 100 + x, 32 + y, COL_BG);
+    // draw_wave_pattern(&wave_active, 0 + x, 0 + y, 1);
+
+    memcpy32(SOUND_WAVE_RAM, wave_active, 16);
+    SOUND_WAVE_MODE ^= SOUND_WAVE_BANK_SELECT(1);
+}
+
 void
 sequencer_tick(void) {
+    wave_ad_tick();
     if (nseq_ticks++ == 0) {
         play_step();
-        return;
     } else if (nseq_ticks == 24) {
         nseq_ticks = 0;
     }
-- 
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