Add latching to ppu

src/app/emu/video/ppu.cc

@@ -590,7 +590,7 @@ void Ppu::HandleVblank() {
   frame_interlace = interlace;  // set if we have a interlaced frame
 }
 
-uint8_t Ppu::Read(uint8_t adr) {
+uint8_t Ppu::Read(uint8_t adr, bool latch) {
   switch (adr) {
     case 0x04:
     case 0x14:
@@ -621,9 +621,9 @@ uint8_t Ppu::Read(uint8_t adr) {
     }
     case 0x37: {
       // TODO: only when ppulatch is set
-      hCount = memory_.h_pos() / 4;
-      vCount = memory_.v_pos();
-      countersLatched = true;
+      if (latch) {
+        LatchHV();
+      }
       return memory_.open_bus();
     }
     case 0x38: {
@@ -711,9 +711,11 @@ uint8_t Ppu::Read(uint8_t adr) {
       val |= ppu2openBus & 0x20;
       val |= countersLatched << 6;
       val |= even_frame << 7;
-      countersLatched = false;  // TODO: only when ppulatch is set
-      hCountSecond = false;
-      vCountSecond = false;
+      if (latch) {
+        countersLatched = false;
+        hCountSecond = false;
+        vCountSecond = false;
+      }
       ppu2openBus = val;
       return val;
     }

src/app/emu/video/ppu.h

@@ -314,6 +314,12 @@ class Ppu : public SharedRom {
   void RunLine(int line);
   void HandlePixel(int x, int y);
 
+  void LatchHV() {
+    hCount = memory_.h_pos() / 4;
+    vCount = memory_.v_pos();
+    countersLatched = true;
+  }
+
   int GetPixel(int x, int y, bool sub, int* r, int* g, int* b);
 
   void EvaluateSprites(int line);
@@ -350,7 +356,7 @@ class Ppu : public SharedRom {
   uint16_t GetOffsetValue(int col, int row);
   int GetPixelForBgLayer(int x, int y, int layer, bool priority);
 
-  uint8_t Read(uint8_t adr);
+  uint8_t Read(uint8_t adr, bool latch);
   void Write(uint8_t adr, uint8_t val);
 
   uint16_t GetVramRemap();