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POWpf's InteropBitmap together with GDI+: high cpu usage
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  1. POWpf's InteropBitmap together with GDI+: high cpu usage
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    copied!<p>I've created a little wpf test application which renders some random rectangles every 30 msec using <strong>System.Drawing.Graphics</strong> and wpf's <strong>InteropBitmap</strong>. I thought InteropBitmap would be faster than WriteableBitmap: It has the ability to update itself from the memory section.</p> <p>While executing the app (screen size 1600 * 1200) the cpu usage of the app is only about <strong>2-10%</strong> with a dual core 3GHz. But the overall cpu usage is about <strong>80-90%</strong>, because the process "System (NT Kernel &amp; System") rises up to 70% ! <strong>EDIT:</strong> And I noticed that the RAM usage periodically increases by more than 1 GB within 15 seconds and then suddenly falls back to its normal level and so on.</p> <p>Maybe the following code can be optimized ? :</p> <pre><code>namespace InteropBitmapTest{ using System; using System.Drawing; using System.Runtime.InteropServices; using System.Windows; using System.Windows.Interop; using System.Windows.Media; using System.Windows.Media.Imaging; using Color = System.Drawing.Color; public partial class Window1 : Window { private System.Drawing.Bitmap gdiBitmap; private Graphics graphics; InteropBitmap interopBitmap; const uint FILE_MAP_ALL_ACCESS = 0xF001F; const uint PAGE_READWRITE = 0x04; private int bpp = PixelFormats.Bgr32.BitsPerPixel / 8; private Random random; private System.Windows.Forms.Timer timer = new System.Windows.Forms.Timer(); SolidBrush[] brushes = new SolidBrush[] { new SolidBrush(Color.Lime), new SolidBrush(Color.White) }; [DllImport("kernel32.dll", SetLastError = true)] static extern IntPtr CreateFileMapping(IntPtr hFile, IntPtr lpFileMappingAttributes, uint flProtect, uint dwMaximumSizeHigh, uint dwMaximumSizeLow, string lpName); [DllImport("kernel32.dll", SetLastError = true)] static extern IntPtr MapViewOfFile(IntPtr hFileMappingObject, uint dwDesiredAccess, uint dwFileOffsetHigh, uint dwFileOffsetLow, uint dwNumberOfBytesToMap); public Window1() { InitializeComponent(); Loaded += Window1_Loaded; WindowState = WindowState.Maximized; timer.Tick += timer_Tick; timer.Interval = 30; random = new Random(); } void Window1_Loaded(object sender, RoutedEventArgs e) { // create interopbitmap, gdi bitmap, get Graphics object CreateBitmaps(); // start drawing 100 gdi+ rectangles every 30 msec: timer.Start(); } void timer_Tick(object sender, EventArgs e) { int width = 50; // Draw 100 gdi+ rectangles : for (int i = 0; i &lt; 100; i++) { int left = random.Next((int)(ActualWidth - width)); int top = random.Next((int)(ActualHeight - width)); graphics.FillRectangle(brushes[left % 2], left, top, width, width); } interopBitmap.Invalidate(); // should only update video memory (and not copy the whole bitmap to video memory before) } void CreateBitmaps() { uint byteCount = (uint) (ActualWidth * ActualHeight * bpp); //Allocate/reserve memory to write to var sectionPointer = CreateFileMapping(new IntPtr(-1), IntPtr.Zero, PAGE_READWRITE, 0, byteCount, null); var mapPointer = MapViewOfFile(sectionPointer, FILE_MAP_ALL_ACCESS, 0, 0, byteCount); var format = PixelFormats.Bgr32; //create the InteropBitmap interopBitmap = Imaging.CreateBitmapSourceFromMemorySection(sectionPointer, (int)ActualWidth, (int)ActualHeight, format, (int)(ActualWidth * format.BitsPerPixel / 8), 0) as InteropBitmap; //create the GDI Bitmap gdiBitmap = new System.Drawing.Bitmap((int)ActualWidth, (int)ActualHeight, (int)ActualWidth * bpp, System.Drawing.Imaging.PixelFormat.Format32bppPArgb, mapPointer); // Get good old GDI Graphics graphics = Graphics.FromImage(gdiBitmap); // set the interopbitmap as Source to the wpf image defined in XAML wpfImage.Source = (BitmapSource) interopBitmap; } }} </code></pre> <p>XAML:</p> <pre><code>&lt;Window x:Class="InteropBitmapTest.Window1" xmlns="http://schemas.microsoft.com/winfx/2006/xaml/presentation" xmlns:x="http://schemas.microsoft.com/winfx/2006/xaml" Title="Window1" Height="300" Width="300"&gt; &lt;Image Name="wpfImage" Stretch="None" /&gt; &lt;/Window&gt; </code></pre>
 

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