PPU: impl scrolling

Sources/PPU/NesPPU.swift

@@ -28,6 +28,9 @@ class NesPPU {
     func tick(_ cycles: UInt8) -> Bool {
         self.cycles += Int(cycles)
         if self.cycles >= 341 {
+            if checkSprite0Hit(self.cycles) {
+                status.setSpriteZeroHit(true)
+            }
             self.cycles = self.cycles - 341
             self.scanline += 1
 
@@ -50,6 +53,12 @@ class NesPPU {
         return false
     }
 
+    func checkSprite0Hit(_ cycle: Int) -> Bool {
+        let y = Int(oamData[0])
+        let x = Int(oamData[0])
+        return (y == scanline) && x <= cycle && mask.showSprites()
+    }
+
     func pollNMI() -> UInt8? {
         let tmp = self.nmiInterrupt
         self.nmiInterrupt = nil

Sources/PPU/Registers/ControlRegister.swift

@@ -70,4 +70,19 @@ struct ControlRegister: OptionSet {
             1
         }
     }
+
+    func nametableAddr() -> UInt16 {
+        switch rawValue & 0b11 {
+        case 0:
+            0x2000
+        case 1:
+            0x2400
+        case 2:
+            0x2800
+        case 3:
+            0x2c00
+        default:
+            fatalError("naemtableAddr: Not possible!")
+        }
+    }
 }