Pissed about trying to fix a number of bugs

Core/Cpu/Z80.cs

@@ -190,6 +190,7 @@ namespace Core.Cpu
 
             // Fetch the next opcode and increment the Program Counter
             byte opcode = ReadMemory(PC++);
+            R = (byte)((R + 1) & 0x7F);
             int tStates = ExecuteOpcode(opcode);
             TotalTStates += tStates;
 

Core/Video/SmsVdp.cs

@@ -18,9 +18,12 @@ namespace Core.Video
 
         private int _tStateCounter = 0;
         private int _currentScanline = 0;
+        private int _lineCounter = 0;
         private byte _statusRegister = 0x00;
 
-        public bool InterruptPending => (_statusRegister & 0x80) != 0 && (Registers[1] & 0x20) != 0;
+        public bool InterruptPending =>
+            ((_statusRegister & 0x80) != 0 && (Registers[1] & 0x20) != 0) || // VBlank
+            ((_statusRegister & 0x40) != 0 && (Registers[0] & 0x10) != 0);   // Line Interrupt
 
         public byte ReadDataPort() // Port 0xBE
         {
@@ -110,6 +113,20 @@ namespace Core.Video
             if (_tStateCounter >= 228)
             {
                 _tStateCounter -= 228;
+                //// --- LINE INTERRUPT LOGIC ---
+                //if (_currentScanline <= 192)
+                //{
+                //    _lineCounter--;
+                //    if (_lineCounter < 0)
+                //    {
+                //        _lineCounter = Registers[10]; // Reload counter
+                //        _statusRegister |= 0x40; // Set Line Interrupt Flag (Bit 6)
+                //    }
+                //}
+                //else
+                //{
+                //    _lineCounter = Registers[10]; // Reload outside active display
+                //}
                 _currentScanline++;
 
                 // Line 192 is the exact moment the screen finishes drawing!
@@ -117,9 +134,17 @@ namespace Core.Video
                 {
                     _statusRegister |= 0x80; // Set Bit 7 (VBlank Flag) to 1
 
-                    RenderBackground(); // <--- DRAW THE FRAME!
+                    if ((Registers[1] & 0x40) != 0)
+                    {
+                        RenderBackground();
                         RenderSprites();
                     }
+                    else
+                    {
+                        // Screen is off! Fill it with black (or the background color)
+                        Array.Fill(FrameBuffer, unchecked((int)0xFF000000));
+                    }
+                }
 
                 // End of the NTSC frame (262 lines)
                 if (_currentScanline > 261)
@@ -220,6 +245,7 @@ namespace Core.Video
 
             // 3. Register 1 determines sprite size (8x8 or 8x16)
             bool is8x16 = (Registers[1] & 0x02) != 0;
+            bool shiftSpritesLeft = (Registers[0] & 0x08) != 0;
 
             // The SMS can draw a maximum of 64 sprites
             for (int i = 0; i < 64; i++)
@@ -261,6 +287,11 @@ namespace Core.Video
                     for (int px = 0; px < 8; px++)
                     {
                         int screenX = x + px;
+                        // THE FIX: Shift the pixel left if commanded!
+                        if (shiftSpritesLeft) screenX -= 8;
+
+                        // If it shifted off the left edge, skip it!
+                        if (screenX < 0 || screenX >= 256) continue;
 
                         // If this pixel is off the right side of the screen, skip it
                         if (screenX >= 256) continue;

Desktop/Desktop.csproj

@@ -11,8 +11,11 @@
   <ItemGroup>
     <None Remove="ROMS\Golden Axe Warrior.sms" />
     <None Remove="ROMS\R-Type.sms" />
+    <None Remove="ROMS\SMSTestSuite.sms" />
     <None Remove="ROMS\Sonic 2.sms" />
     <None Remove="ROMS\Sonic.sms" />
+    <None Remove="ROMS\zexall.sms" />
+    <None Remove="ROMS\zexdoc.sms" />
   </ItemGroup>
 
   <ItemGroup>
@@ -22,12 +25,21 @@
     <EmbeddedResource Include="ROMS\R-Type.sms">
       <CopyToOutputDirectory>Always</CopyToOutputDirectory>
     </EmbeddedResource>
+    <EmbeddedResource Include="ROMS\SMSTestSuite.sms">
+      <CopyToOutputDirectory>Always</CopyToOutputDirectory>
+    </EmbeddedResource>
     <EmbeddedResource Include="ROMS\Sonic 2.sms">
       <CopyToOutputDirectory>Always</CopyToOutputDirectory>
     </EmbeddedResource>
     <EmbeddedResource Include="ROMS\Sonic.sms">
       <CopyToOutputDirectory>Always</CopyToOutputDirectory>
     </EmbeddedResource>
+    <EmbeddedResource Include="ROMS\zexall.sms">
+      <CopyToOutputDirectory>Always</CopyToOutputDirectory>
+    </EmbeddedResource>
+    <EmbeddedResource Include="ROMS\zexdoc.sms">
+      <CopyToOutputDirectory>Always</CopyToOutputDirectory>
+    </EmbeddedResource>
   </ItemGroup>
 
   <ItemGroup>

Desktop/Form1.Designer.cs

@@ -28,7 +28,6 @@
         /// </summary>
         private void InitializeComponent()
         {
-            pbScreen = new PictureBox();
             menuStrip1 = new MenuStrip();
             fileToolStripMenuItem = new ToolStripMenuItem();
             openToolStripMenuItem = new ToolStripMenuItem();
@@ -41,19 +40,9 @@
             resetToolStripMenuItem = new ToolStripMenuItem();
             helpToolStripMenuItem = new ToolStripMenuItem();
             aboutToolStripMenuItem = new ToolStripMenuItem();
-            ((System.ComponentModel.ISupportInitialize)pbScreen).BeginInit();
             menuStrip1.SuspendLayout();
             SuspendLayout();
             // 
-            // pbScreen
-            // 
-            pbScreen.Location = new Point(12, 36);
-            pbScreen.Name = "pbScreen";
-            pbScreen.Size = new Size(768, 576);
-            pbScreen.SizeMode = PictureBoxSizeMode.Zoom;
-            pbScreen.TabIndex = 1;
-            pbScreen.TabStop = false;
-            // 
             // menuStrip1
             // 
             menuStrip1.ImageScalingSize = new Size(24, 24);
@@ -145,13 +134,11 @@
             AutoScaleDimensions = new SizeF(10F, 25F);
             AutoScaleMode = AutoScaleMode.Font;
             ClientSize = new Size(791, 622);
-            Controls.Add(pbScreen);
             Controls.Add(menuStrip1);
             MainMenuStrip = menuStrip1;
             Margin = new Padding(4);
             Name = "ParsonsForm1";
             Text = "Form1";
-            ((System.ComponentModel.ISupportInitialize)pbScreen).EndInit();
             menuStrip1.ResumeLayout(false);
             menuStrip1.PerformLayout();
             ResumeLayout(false);
@@ -159,7 +146,6 @@
         }
 
         #endregion
-        private PictureBox pbScreen;
         private MenuStrip menuStrip1;
         private ToolStripMenuItem fileToolStripMenuItem;
         private ToolStripMenuItem openToolStripMenuItem;

Desktop/Form1.cs

@@ -40,6 +40,8 @@ namespace Desktop
             this.KeyPreview = true;
             this.KeyDown += Form1_KeyDown;
             this.KeyUp += Form1_KeyUp;
+            this.DoubleBuffered = true;
+            this.ResizeRedraw = true;
         }
 
         private void DrawScreen()
@@ -48,11 +50,34 @@ namespace Desktop
             var data = _screenBitmap.LockBits(new Rectangle(0, 0, 256, 192), ImageLockMode.WriteOnly, PixelFormat.Format32bppArgb);
             Marshal.Copy(_machine.VideoProcessor.FrameBuffer, 0, data.Scan0, _machine.VideoProcessor.FrameBuffer.Length);
             _screenBitmap.UnlockBits(data);
-
+            this.Invalidate();
-            // Update the PictureBox
-            pbScreen.Image = _screenBitmap;
             TotalFrameCount++;
         }
+        protected override void OnPaint(PaintEventArgs e)
+        {
+            // Always call the base method so Windows can draw your MenuStrip!
+            base.OnPaint(e);
+
+            if (_screenBitmap != null)
+            {
+                // 1. Set the rendering mode for perfect, chunky retro pixels!
+                e.Graphics.InterpolationMode = System.Drawing.Drawing2D.InterpolationMode.NearestNeighbor;
+                e.Graphics.PixelOffsetMode = System.Drawing.Drawing2D.PixelOffsetMode.Half;
+
+                // 2. Calculate the drawing area. 
+                // We start drawing BELOW the MenuStrip so it doesn't get covered up.
+                int topOffset = menuStrip1.Height; // Change 'menuStrip1' if your menu has a different (Name)
+                Rectangle renderArea = new Rectangle(
+                    0,
+                    topOffset,
+                    this.ClientSize.Width,
+                    this.ClientSize.Height - topOffset
+                );
+
+                // 3. Blast the bitmap directly onto the graphics card buffer!
+                e.Graphics.DrawImage(_screenBitmap, renderArea);
+            }
+        }
 
         public void StartEmulator()
         {