Outline PPU cycles per scanline, get APU cycles

src/app/emu/apu.cc

@@ -21,15 +21,23 @@ void APU::Init() {
 }
 
 void APU::Reset() {
-  // Render background layers
-  // ...
+  // Reset the clock
+  ResetAccumulatedTime();
 
-  // Render sprites
+  // Reset the SPC700
   // ...
 }
 
 void APU::Update() {
-  // ...
+  auto cycles_to_run = GetCycleCount();
+
+  for (auto i = 0; i < cycles_to_run; ++i) {
+    // Update the APU
+    // ...
+
+    // Update the SPC700
+    // ...
+  }
 }
 
 uint8_t APU::ReadRegister(uint16_t address) {

src/app/emu/ppu.cc

@@ -13,14 +13,6 @@ namespace emu {
 PPU::PPU(Memory& memory) : memory_(memory) {}
 
 void PPU::RenderScanline() {
-  // Render background layers
-  // ...
-
-  // Render sprites
-  // ...
-}
-
-void PPU::Update() {
   // Fetch the tile data from VRAM, tile map data from memory, and palette data
   // from CGRAM
   UpdateTileData();     // Fetches the tile data from VRAM and stores it in an
@@ -54,6 +46,39 @@ void PPU::Update() {
                          // (e.g., SDL2)
 }
 
+void PPU::Update() {
+  auto cycles_to_run = GetCycleCount();
+
+  UpdateInternalState(cycles_to_run);
+
+  // Render however many scanlines we're supposed to.
+  if (currentScanline < visibleScanlines) {
+    // Render the current scanline
+    // This involves fetching tile data, applying palette colors, handling
+    // sprite priorities, etc.
+    RenderScanline();
+
+    // Increment the current scanline
+    currentScanline++;
+  }
+}
+
+void PPU::UpdateInternalState(int cycles) {
+  // Update the PPU's internal state based on the number of cycles
+  cycleCount += cycles;
+
+  // Check if it's time to move to the next scanline
+  if (cycleCount >= cyclesPerScanline) {
+    currentScanline++;
+    cycleCount -= cyclesPerScanline;
+
+    // If we've reached the end of the frame, reset to the first scanline
+    if (currentScanline >= totalScanlines) {
+      currentScanline = 0;
+    }
+  }
+}
+
 // Reads a byte from the specified PPU register
 uint8_t PPU::ReadRegister(uint16_t address) {
   switch (address) {

src/app/emu/ppu.h

@@ -645,6 +645,7 @@ class PPU : public Clock {
 
   // Runs the PPU for one frame.
   void Update();
+  void UpdateInternalState(int cycles);
 
   // Reads a byte from the specified PPU register
   uint8_t ReadRegister(uint16_t address);
@@ -734,6 +735,12 @@ class PPU : public Clock {
 
   // The CGRAM memory area holds the color palette data.
   std::array<uint8_t, 512> cgram_;
+
+  int cycleCount = 0;
+  int currentScanline = 0;
+  const int cyclesPerScanline = 341;  // SNES PPU has 341 cycles per scanline
+  const int totalScanlines = 262;     // SNES PPU has 262 scanlines per frame
+  const int visibleScanlines = 224;   // SNES PPU renders 224 visible scanlines
 };
 
 }  // namespace emu