Drawing Libraries

The previous example demonstrated how we can create a managed accessor for a WriteableBitmap. But it worked only because we used a pixel format that happen to have built-in support also in KGy SOFT Drawing Libraries. In fact, the libraries provide support for any custom pixel format. The CreateBitmapData methods have several overloads that allow you to specify a custom pixel format along with a couple of delegates to be called when pixels are read or written:

// Gray8 format has no built-in support
var bitmap = new WriteableBitmap(width, height, dpiX, dpiY, PixelFormats.Gray8, null);

// But we can specify how to use it
var customPixelFormat = new PixelFormatInfo { BitsPerPixel = 8, Grayscale = true };
Func<ICustomBitmapDataRow, int, Color32> getPixel =
    (row, x) => Color32.FromGray(row.UnsafeGetRefAs<byte>(x));
Action<ICustomBitmapDataRow, int, Color32> setPixel =
    (row, x, c) => c.Blend(row.BitmapData.BackColor).GetBrightness();

// Now we specify also a dispose callback to be executed when the returned instance is disposed:
return BitmapDataFactory.CreateBitmapData(
    bitmap.BackBuffer, new Size(bitmap.PixelWidth, bitmap.PixelHeight), bitmap.BackBufferStride,
    customPixelFormat, getPixel, setPixel,
    disposeCallback: () =>
    {
        bitmap.AddDirtyRect(new Int32Rect(0, 0, bitmap.PixelWidth, bitmap.PixelHeight));
        bitmap.Unlock();
    });

💡 Tip: See also the Xamarin and MAUI examples that demonstrate how to create a bitmap data for SkiaSharp’s SKBitmap type.

Note that there are different overloads for indexed formats where you have to specify how to read/write a palette index. Please also note that these delegates work with 32-bit color structures (just like usual GetPixel/SetPixel) so wider formats will be quantized into the ARGB8888 color space (or BGRA8888, using the alternative terminology) when getting/setting pixels but this is how regular formats work, too. Anyway, you can always access the actual underlying data of whatever format by the aforementioned IReadableBitmapDataRow.ReadRaw and IWritableBitmapDataRow.WriteRaw methods.