Minor changes

src/vcpu.c

@@ -8,6 +8,7 @@ VCPU_State State;
 
 void VCPUInit(){
   State.PC=ADDR_ROM;
+  State.S=0;
 }
 
 void VCPUFetch(){
@@ -54,12 +55,26 @@ void VCPUExecute(){
     State.I=State.NNN;
     break
       ;;
-  case 0xD:
+  case 0xD: // Draw a sprite
     int X=State.V[State.X]%63;
     int Y=State.V[State.Y]%31;
     State.V[REG_FLAG]=0; // Set flag to 0
+    int width,height;
+    ScreenWH(&width,&height);
     for(char row=0;row<State.N;row++){
-      
+      // Stop if row out of screen
+      if(Y+row>=height)
+        break;
+      char sprite;
+      MemRead(&sprite,1,State.I+row); // Load sprite
+      // Draw sprite
+      for(int shift=0;shift<8;shift++){
+        // Stop if column is out of screen
+        if(X+shift >= width)
+          break;
+        if(ScreenPixelApply(X+shift,Y+row,(sprite>>(7-shift))&0x1))
+          State.V[REG_FLAG]=1;
+      }
     }
     break;
     ;;