Improved readme

Author: DarthAffe

README.md

@@ -1,2 +1,60 @@
 # ScreenCapture
 Vortice based Desktop Duplication
+
+## Usage
+```csharp
+// Sets the DPI-awareness of the application - this is required for capturing
+DPIAwareness.Initalize();
+
+// Create a screen-capture service
+IScreenCaptureService screenCaptureService = new DX11ScreenCaptureService();
+
+// Get all available graphics cards
+IEnumerable<GraphicsCard> graphicsCards = screenCaptureService.GetGraphicsCards();
+
+// Get the displays from the graphics card(s) you are interested in
+IEnumerable<Display> displays = screenCaptureService.GetDisplays(graphicsCards.First());
+
+// Create a screen-capture for all screens you want to capture
+IScreenCapture screenCapture = screenCaptureService.GetScreenCapture(displays.First());
+
+// Register the regions you want to capture om the screen
+// Capture the whole screen
+CaptureZone fullscreen = screenCapture.RegisterCaptureZone(0, 0, screenCapture.Display.Width, screenCapture.Display.Height);
+// Capture a 100x100 region at the top left and scale it down to 50x50
+CaptureZone topLeft = screenCapture.RegisterCaptureZone(0, 0, 100, 100, downscaleLevel: 1);
+
+// Capture the screen
+// This should be done in a loop on a seperate thread as CaptureScreen blocks if the screen is not updated (still image)
+screenCapture.CaptureScreen();
+
+// Do something with the captured image - e.g. access all pixels (same could be done with topLeft)
+// Locking is not neccessary in that case as we're capturing in the same thread,
+// but when using a threaded-approach (which is recommended) it prevents potential tearing of the data in the buffer
+lock (fullscreen.Buffer)
+{
+    // Since the size of the capture can be bigger than the size of our captured region due to size constraints on the GPU,
+    // we need to use this for the stride. 
+    // The 4 is the amount of bytes per pixel which is always 4 for the DX11ScreenCapture
+    int stride = fullscreen.CaptureWidth * 4;
+
+    Span<byte> data = new(fullscreen.Buffer);
+
+    // Iterate all rows of the image
+    for (int y = 0; y < fullscreen.Height; y++)
+    {
+        // Select the actual data of the row
+        Span<byte> row = data.Slice(y * stride, fullscreen.Width * 4);
+
+        // Iterate all pixels
+        for (int x = 0; x < fullscreen.Width; x += 4)
+        {
+            // Data is in BGRA format for the DX11ScreenCapture
+            byte b = row[x];
+            byte g = row[x + 1];
+            byte r = row[x + 2];
+            byte a = row[x + 3];
+        }
+    }
+}
+```