feat(apu): add ChannelOutputs struct and channel_outputs() method

src/native_core/apu/api.rs

@@ -1,4 +1,4 @@
-use super::types::{Apu, ApuStateTail};
+use super::types::{Apu, ApuStateTail, ChannelOutputs};
 
 impl Apu {
     pub fn new() -> Self {
@@ -287,4 +287,74 @@ impl Apu {
         self.noise_timer_counter = state.noise_timer_counter;
         self.noise_lfsr = if state.noise_lfsr == 0 { 1 } else { state.noise_lfsr };
     }
+
+    pub fn channel_outputs(&self) -> ChannelOutputs {
+        const PULSE_DUTY_TABLE: [[u8; 8]; 4] = [
+            [0, 1, 0, 0, 0, 0, 0, 0],
+            [0, 1, 1, 0, 0, 0, 0, 0],
+            [0, 1, 1, 1, 1, 0, 0, 0],
+            [1, 0, 0, 1, 1, 1, 1, 1],
+        ];
+        const TRIANGLE_SEQUENCE: [u8; 32] = [
+            15, 14, 13, 12, 11, 10, 9, 8, 7, 6, 5, 4, 3, 2, 1, 0,
+            0, 1, 2, 3, 4, 5, 6, 7, 8, 9, 10, 11, 12, 13, 14, 15,
+        ];
+
+        let pulse1 = {
+            let duty = (self.io[0x00] >> 6) as usize;
+            let step = self.pulse_duty_step[0] as usize;
+            let volume = if (self.io[0x00] & 0x10) != 0 {
+                self.io[0x00] & 0x0F
+            } else {
+                self.envelope_decay[0]
+            };
+            let active = (self.channel_enable_mask & 0x01) != 0
+                && self.length_counters[0] > 0
+                && PULSE_DUTY_TABLE[duty][step] != 0
+                && !self.sweep_mutes_channel(0, 0x02);
+            if active { volume } else { 0 }
+        };
+
+        let pulse2 = {
+            let duty = (self.io[0x04] >> 6) as usize;
+            let step = self.pulse_duty_step[1] as usize;
+            let volume = if (self.io[0x04] & 0x10) != 0 {
+                self.io[0x04] & 0x0F
+            } else {
+                self.envelope_decay[1]
+            };
+            let active = (self.channel_enable_mask & 0x02) != 0
+                && self.length_counters[1] > 0
+                && PULSE_DUTY_TABLE[duty][step] != 0
+                && !self.sweep_mutes_channel(1, 0x06);
+            if active { volume } else { 0 }
+        };
+
+        let triangle = {
+            let active = (self.channel_enable_mask & 0x04) != 0
+                && self.length_counters[2] > 0
+                && self.triangle_linear_counter > 0;
+            if active {
+                TRIANGLE_SEQUENCE[self.triangle_step as usize & 0x1F]
+            } else {
+                0
+            }
+        };
+
+        let noise = {
+            let volume = if (self.io[0x0C] & 0x10) != 0 {
+                self.io[0x0C] & 0x0F
+            } else {
+                self.envelope_decay[2]
+            };
+            let active = (self.channel_enable_mask & 0x08) != 0
+                && self.length_counters[3] > 0
+                && (self.noise_lfsr & 1) == 0;
+            if active { volume } else { 0 }
+        };
+
+        let dmc = self.dmc_output_level;
+
+        ChannelOutputs { pulse1, pulse2, triangle, noise, dmc }
+    }
 }