Minor changes

src/main.c

@@ -7,7 +7,7 @@ int main(int argc, char *argv[])
 
   // Initialize
   MemInit();
-  MemLoadROM("../roms/2-ibm-logo.ch8");
+  MemLoadROM("../roms/logo_chip8.ch8");
 
   ScreenInit(800,400);
   VCPUInit();

src/screen.c

@@ -15,7 +15,7 @@ void ScreenInit(int width, int height){
 
   SetTraceLogLevel(LOG_ERROR); // Disable anoying raylib logs
   InitWindow(width, height, "Chip-8 Emulator");
-  SetTargetFPS(60); // Set game to run at 60 frames-per-second
+  SetTargetFPS(80); // Set game to run at 60 frames-per-second
 }
 
 void ScreenClear() {
@@ -40,8 +40,11 @@ void ScreenUpdate(){
   EndDrawing();
 }
 
-void ScreenSetPixel(int x, int y, unsigned char state){
+char ScreenPixelApply(int x, int y, unsigned char state){
-  Screen.pixels[x+y*64]=(state==0) ? 0: 1;
+  if(Screen.pixels[x+y*64] != 0 && state != 0)
+    return 1;
+  Screen.pixels[x+y*64]=state;
+  return 0;
 }
 
 void ScreenPixelFlip(int x, int y){
@@ -51,6 +54,11 @@ void ScreenPixelFlip(int x, int y){
     Screen.pixels[x+y*64]=0;
 }
 
+void ScreenWH(int *width, int *height){
+  *width=64;
+  *height=32;
+}
+
 void ScreenClose(){
   CloseWindow(); // Close window and OpenGL context
 }

src/screen.h

@@ -15,7 +15,7 @@ typedef struct SCREEN_DATA {
 
 void ScreenInit(int width, int height);
 void ScreenClear();
-void ScreenSetPixel(int x, int y, unsigned char state);
+char ScreenPixelApply(int x, int y, unsigned char state);
-void ScreenPixelFlip(int x, int y);
+void ScreenWH(int *width, int *height);
 void ScreenUpdate();
 void ScreenClose();

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;
     ;;