Initial commit: NES emulator with GTK4 desktop frontend

Full NES emulation: CPU, PPU, APU, 47 mappers, iNES/NES 2.0 parsing.
GTK4 desktop client with HeaderBar, pixel-perfect Cairo rendering,
drag-and-drop ROM loading, and keyboard shortcuts.
187 tests covering core emulation, mappers, and runtime.

src/native_core/ppu/api/persistence.rs

@@ -0,0 +1,108 @@
+use super::*;
+
+impl Ppu {
+    pub fn save_state(&self, out: &mut Vec<u8>) {
+        out.extend_from_slice(&self.vram);
+        out.extend_from_slice(&self.palette_ram);
+        out.extend_from_slice(&self.oam);
+        out.push(self.ctrl);
+        out.push(self.mask);
+        out.push(self.status);
+        out.push(self.oam_addr);
+        out.push(u8::from(self.write_latch));
+        out.extend_from_slice(&self.vram_addr.to_le_bytes());
+        out.extend_from_slice(&self.temp_addr.to_le_bytes());
+        out.push(self.fine_x);
+        out.push(self.scroll_x);
+        out.push(self.scroll_y);
+        out.push(self.read_buffer);
+        out.push(self.io_latch);
+        out.extend_from_slice(&self.bg_shift_pattern_lo.to_le_bytes());
+        out.extend_from_slice(&self.bg_shift_pattern_hi.to_le_bytes());
+        out.extend_from_slice(&self.bg_shift_attr_lo.to_le_bytes());
+        out.extend_from_slice(&self.bg_shift_attr_hi.to_le_bytes());
+        out.push(self.next_tile_id);
+        out.push(self.next_tile_attr);
+        out.push(self.next_tile_lsb);
+        out.push(self.next_tile_msb);
+        out.push(self.sprite_count);
+        out.extend_from_slice(&self.sprite_indices);
+        out.push(self.next_sprite_count);
+        out.extend_from_slice(&self.next_sprite_indices);
+    }
+
+    pub fn load_state(&mut self, data: &[u8]) -> Result<usize, String> {
+        let mut cursor = 0usize;
+        self.vram.copy_from_slice(sio::take_exact(
+            data,
+            &mut cursor,
+            VRAM_SIZE,
+            PPU_STATE_CTX,
+        )?);
+        self.palette_ram.copy_from_slice(sio::take_exact(
+            data,
+            &mut cursor,
+            PALETTE_SIZE,
+            PPU_STATE_CTX,
+        )?);
+        self.oam
+            .copy_from_slice(sio::take_exact(data, &mut cursor, OAM_SIZE, PPU_STATE_CTX)?);
+        self.ctrl = sio::take_u8(data, &mut cursor, PPU_STATE_CTX)?;
+        self.mask = sio::take_u8(data, &mut cursor, PPU_STATE_CTX)?;
+        self.status = sio::take_u8(data, &mut cursor, PPU_STATE_CTX)?;
+        self.oam_addr = sio::take_u8(data, &mut cursor, PPU_STATE_CTX)?;
+        self.write_latch = sio::take_u8(data, &mut cursor, PPU_STATE_CTX)? != 0;
+        self.vram_addr = sio::take_u16(data, &mut cursor, PPU_STATE_CTX)?;
+        self.vram_addr &= 0x3FFF;
+        self.temp_addr = sio::take_u16(data, &mut cursor, PPU_STATE_CTX)? & 0x3FFF;
+        self.fine_x = sio::take_u8(data, &mut cursor, PPU_STATE_CTX)?;
+        self.scroll_x = sio::take_u8(data, &mut cursor, PPU_STATE_CTX)?;
+        self.scroll_y = sio::take_u8(data, &mut cursor, PPU_STATE_CTX)?;
+        self.read_buffer = sio::take_u8(data, &mut cursor, PPU_STATE_CTX)?;
+        self.io_latch = if cursor < data.len() {
+            sio::take_u8(data, &mut cursor, PPU_STATE_CTX)?
+        } else {
+            0
+        };
+        if cursor + 30 <= data.len() {
+            self.bg_shift_pattern_lo = sio::take_u16(data, &mut cursor, PPU_STATE_CTX)?;
+            self.bg_shift_pattern_hi = sio::take_u16(data, &mut cursor, PPU_STATE_CTX)?;
+            self.bg_shift_attr_lo = sio::take_u16(data, &mut cursor, PPU_STATE_CTX)?;
+            self.bg_shift_attr_hi = sio::take_u16(data, &mut cursor, PPU_STATE_CTX)?;
+            self.next_tile_id = sio::take_u8(data, &mut cursor, PPU_STATE_CTX)?;
+            self.next_tile_attr = sio::take_u8(data, &mut cursor, PPU_STATE_CTX)?;
+            self.next_tile_lsb = sio::take_u8(data, &mut cursor, PPU_STATE_CTX)?;
+            self.next_tile_msb = sio::take_u8(data, &mut cursor, PPU_STATE_CTX)?;
+            self.sprite_count = sio::take_u8(data, &mut cursor, PPU_STATE_CTX)?;
+            self.sprite_indices.copy_from_slice(sio::take_exact(
+                data,
+                &mut cursor,
+                8,
+                PPU_STATE_CTX,
+            )?);
+            self.next_sprite_count = sio::take_u8(data, &mut cursor, PPU_STATE_CTX)?;
+            self.next_sprite_indices.copy_from_slice(sio::take_exact(
+                data,
+                &mut cursor,
+                8,
+                PPU_STATE_CTX,
+            )?);
+        } else {
+            self.bg_shift_pattern_lo = 0;
+            self.bg_shift_pattern_hi = 0;
+            self.bg_shift_attr_lo = 0;
+            self.bg_shift_attr_hi = 0;
+            self.next_tile_id = 0;
+            self.next_tile_attr = 0;
+            self.next_tile_lsb = 0;
+            self.next_tile_msb = 0;
+            self.sprite_count = 0;
+            self.sprite_indices = [0; 8];
+            self.next_sprite_count = 0;
+            self.next_sprite_indices = [0; 8];
+        }
+        self.scroll_events.clear();
+        self.scroll_events.push(self.current_scroll_event(0, 0));
+        Ok(cursor)
+    }
+}