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WriteableBitmap Class

Provides a BitmapSource that can be written to and updated.

Namespace:  System.Windows.Media.Imaging
Assembly:  PresentationCore (in PresentationCore.dll)

public sealed class WriteableBitmap : BitmapSource

The WriteableBitmap type exposes the following members.

  NameDescription
Public methodWriteableBitmap(BitmapSource)Initializes a new instance of the WriteableBitmap class using the given BitmapSource.
Public methodWriteableBitmap(Int32, Int32, Double, Double, PixelFormat, BitmapPalette)Initializes a new instance of the WriteableBitmap class with the specified parameters.
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  NameDescription
Public propertyBackBufferGets a pointer to the back buffer.
Public propertyBackBufferStrideGets a value indicating the number of bytes in a single row of pixel data.
Public propertyCanFreezeGets a value that indicates whether the object can be made unmodifiable. (Inherited from Freezable.)
Public propertyDependencyObjectTypeGets the DependencyObjectType that wraps the CLR type of this instance.  (Inherited from DependencyObject.)
Public propertyDispatcherGets the Dispatcher this DispatcherObject is associated with. (Inherited from DispatcherObject.)
Public propertyDpiXGets the horizontal dots per inch (dpi) of the image.  (Inherited from BitmapSource.)
Public propertyDpiYGets the vertical dots per inch (dpi) of the image.  (Inherited from BitmapSource.)
Public propertyFormatGets the native PixelFormat of the bitmap data. (Inherited from BitmapSource.)
Public propertyHasAnimatedPropertiesGets a value that indicates whether one or more AnimationClock objects is associated with any of this object's dependency properties. (Inherited from Animatable.)
Public propertyHeightGets the height of the source bitmap in device-independent units (1/96th inch per unit).  (Inherited from BitmapSource.)
Public propertyIsDownloadingGets a value that indicates whether the BitmapSource content is currently downloading. (Inherited from BitmapSource.)
Public propertyIsFrozenGets a value that indicates whether the object is currently modifiable. (Inherited from Freezable.)
Public propertyIsSealedGets a value that indicates whether this instance is currently sealed (read-only). (Inherited from DependencyObject.)
Public propertyMetadataGets the metadata that is associated with this bitmap image. (Inherited from BitmapSource.)
Public propertyPaletteGets the color palette of the bitmap, if one is specified. (Inherited from BitmapSource.)
Public propertyPixelHeightGets the height of the bitmap in pixels. (Inherited from BitmapSource.)
Public propertyPixelWidthGets the width of the bitmap in pixels. (Inherited from BitmapSource.)
Public propertyWidthGets the width of the bitmap in device-independent units (1/96th inch per unit).  (Inherited from BitmapSource.)
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  NameDescription
Public methodAddDirtyRectSpecifies the area of the bitmap that changed.
Public methodApplyAnimationClock(DependencyProperty, AnimationClock)Applies an AnimationClock to the specified DependencyProperty. If the property is already animated, the SnapshotAndReplace handoff behavior is used. (Inherited from Animatable.)
Public methodApplyAnimationClock(DependencyProperty, AnimationClock, HandoffBehavior)Applies an AnimationClock to the specified DependencyProperty. If the property is already animated, the specified HandoffBehavior is used. (Inherited from Animatable.)
Public methodBeginAnimation(DependencyProperty, AnimationTimeline)Applies an animation to the specified DependencyProperty. The animation is started when the next frame is rendered. If the specified property is already animated, the SnapshotAndReplace handoff behavior is used. (Inherited from Animatable.)
Public methodBeginAnimation(DependencyProperty, AnimationTimeline, HandoffBehavior)Applies an animation to the specified DependencyProperty. The animation is started when the next frame is rendered. If the specified property is already animated, the specified HandoffBehavior is used. (Inherited from Animatable.)
Public methodCheckAccessDetermines whether the calling thread has access to this DispatcherObject. (Inherited from DispatcherObject.)
Public methodClearValue(DependencyProperty)Clears the local value of a property. The property to be cleared is specified by a DependencyProperty identifier. (Inherited from DependencyObject.)
Public methodClearValue(DependencyPropertyKey)Clears the local value of a read-only property. The property to be cleared is specified by a DependencyPropertyKey. (Inherited from DependencyObject.)
Public methodCloneCreates a modifiable clone of this WriteableBitmap, making deep copies of this object's values. When copying dependency properties, this method copies resource references and data bindings (but they might no longer resolve) but not animations or their current values.
Public methodCloneCurrentValueCreates a modifiable clone of this ByteAnimationUsingKeyFrames object, making deep copies of this object's current values. Resource references, data bindings, and animations are not copied, but their current values are.
Public methodCoerceValueCoerces the value of the specified dependency property. This is accomplished by invoking any CoerceValueCallback function specified in property metadata for the dependency property as it exists on the calling DependencyObject. (Inherited from DependencyObject.)
Public methodCopyPixels(Array, Int32, Int32)Copies the bitmap pixel data into an array of pixels with the specified stride, starting at the specified offset. (Inherited from BitmapSource.)
Public methodCopyPixels(Int32Rect, Array, Int32, Int32)Copies the bitmap pixel data within the specified rectangle into an array of pixels that has the specified stride starting at the specified offset. (Inherited from BitmapSource.)
Public methodCopyPixels(Int32Rect, IntPtr, Int32, Int32)Copies the bitmap pixel data within the specified rectangle (Inherited from BitmapSource.)
Public methodEqualsDetermines whether a provided DependencyObject is equivalent to the current DependencyObject. (Inherited from DependencyObject.)
Public methodFreeze()Makes the current object unmodifiable and sets its IsFrozen property to true. (Inherited from Freezable.)
Public methodGetAnimationBaseValueReturns the non-animated value of the specified DependencyProperty. (Inherited from Animatable.)
Public methodGetAsFrozenCreates a frozen copy of the Freezable, using base (non-animated) property values. Because the copy is frozen, any frozen sub-objects are copied by reference. (Inherited from Freezable.)
Public methodGetCurrentValueAsFrozenCreates a frozen copy of the Freezable using current property values. Because the copy is frozen, any frozen sub-objects are copied by reference. (Inherited from Freezable.)
Public methodGetHashCodeGets a hash code for this DependencyObject. (Inherited from DependencyObject.)
Public methodGetLocalValueEnumeratorCreates a specialized enumerator for determining which dependency properties have locally set values on this DependencyObject. (Inherited from DependencyObject.)
Public methodGetTypeGets the Type of the current instance. (Inherited from Object.)
Public methodGetValueReturns the current effective value of a dependency property on this instance of a DependencyObject. (Inherited from DependencyObject.)
Public methodInvalidatePropertyRe-evaluates the effective value for the specified dependency property (Inherited from DependencyObject.)
Public methodLockReserves the back buffer for updates.
Public methodReadLocalValueReturns the local value of a dependency property, if it exists. (Inherited from DependencyObject.)
Public methodSetCurrentValueSets the value of a dependency property without changing its value source. (Inherited from DependencyObject.)
Public methodSetValue(DependencyProperty, Object)Sets the local value of a dependency property, specified by its dependency property identifier. (Inherited from DependencyObject.)
Public methodSetValue(DependencyPropertyKey, Object)Sets the local value of a read-only dependency property, specified by the DependencyPropertyKey identifier of the dependency property. (Inherited from DependencyObject.)
Protected methodShouldSerializePropertyReturns a value that indicates whether serialization processes should serialize the value for the provided dependency property. (Inherited from DependencyObject.)
Public methodToString() Creates a string representation of this object based on the current culture. (Inherited from ImageSource.)
Public methodToString(IFormatProvider)Creates a string representation of this object based on the IFormatProvider passed in. If the provider is null, the CurrentCulture is used. (Inherited from ImageSource.)
Public methodTryLockAttempts to lock the bitmap, waiting for no longer than the specified length of time.
Public methodUnlockReleases the back buffer to make it available for display.
Public methodVerifyAccessEnforces that the calling thread has access to this DispatcherObject. (Inherited from DispatcherObject.)
Public methodWritePixels(Int32Rect, Array, Int32, Int32)Updates the pixels in the specified region of the bitmap.
Public methodWritePixels(Int32Rect, IntPtr, Int32, Int32)Updates the pixels in the specified region of the bitmap.
Public methodWritePixels(Int32Rect, Array, Int32, Int32, Int32)Updates the pixels in the specified region of the bitmap.
Public methodWritePixels(Int32Rect, IntPtr, Int32, Int32, Int32, Int32)Updates the pixels in the specified region of the bitmap.
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  NameDescription
Public eventChangedOccurs when the Freezable or an object it contains is modified. (Inherited from Freezable.)
Public eventDecodeFailedOccurs when the image fails to load, due to a corrupt image header. (Inherited from BitmapSource.)
Public eventDownloadCompletedOccurs when the bitmap content has been completely downloaded. (Inherited from BitmapSource.)
Public eventDownloadFailedOccurs when the bitmap content failed to download. (Inherited from BitmapSource.)
Public eventDownloadProgressOccurs when the download progress of the bitmap content has changed. (Inherited from BitmapSource.)
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  NameDescription
Explicit interface implemetationPrivate methodIFormattable.ToStringFormats the value of the current instance using the specified format. (Inherited from ImageSource.)
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Use the WriteableBitmap class to update and render a bitmap on a per-frame basis. This is useful for generating algorithmic content, such as a fractal image, and for data visualization, such as a music visualizer.

The WriteableBitmap class uses two buffers. The back buffer is allocated in system memory and accumulates content that is not currently displayed. The front buffer is allocated in system memory and contains the content that is currently displayed. The rendering system copies the front buffer to video memory for display.

Two threads use these buffers. The user interface (UI) thread generates the UI but does not present it to the screen. The UI thread responds to user input, timers, and other events. An application can have multiple UI threads. The render thread composes and renders changes from the UI thread. There is only one render thread per application.

The UI thread writes content to the back buffer. The render thread reads content from the front buffer and copies it to video memory. Changes to the back buffer are tracked with changed rectangular regions.

Call one of the WritePixels overloads to update and display content in the back buffer automatically.

For greater control over updates, and for multi-threaded access to the back buffer, use the following workflow.

  1. Call the Lock method to reserve the back buffer for updates.

  2. Obtain a pointer to the back buffer by accessing the BackBuffer property.

  3. Write changes to the back buffer. Other threads may write changes to the back buffer when the WriteableBitmap is locked.

  4. Call the AddDirtyRect method to indicate areas that have changed.

  5. Call the Unlock method to release the back buffer and allow presentation to the screen.

When updates are sent to the rendering thread, the rendering thread copies the changed rectangles from the back buffer to the front buffer. The rendering system controls this exchange to avoid deadlocks and redraw artifacts, such as "tearing".

The following example demonstrates how a WriteableBitmap can be used as the source of an Image to draw pixels when the mouse moves.

using System;
using System.Windows;
using System.Windows.Controls;
using System.Windows.Media;
using System.Windows.Media.Imaging;
using System.Windows.Input;

namespace WriteableBitmapDemo
{
    class Program
    {
        static WriteableBitmap writeableBitmap;
        static Window w;
        static Image i;

        [STAThread]
        static void Main(string[] args)
        {
            i = new Image();
            RenderOptions.SetBitmapScalingMode(i, BitmapScalingMode.NearestNeighbor);
            RenderOptions.SetEdgeMode(i, EdgeMode.Aliased);

            w = new Window();
            w.Content = i;
            w.Show();

            writeableBitmap = new WriteableBitmap(
                (int)w.ActualWidth, 
                (int)w.ActualHeight, 
                96, 
                96, 
                PixelFormats.Bgr32, 
                null);

            i.Source = writeableBitmap;

            i.Stretch = Stretch.None;
            i.HorizontalAlignment = HorizontalAlignment.Left;
            i.VerticalAlignment = VerticalAlignment.Top;

            i.MouseMove += new MouseEventHandler(i_MouseMove);
            i.MouseLeftButtonDown += 
                new MouseButtonEventHandler(i_MouseLeftButtonDown);
            i.MouseRightButtonDown += 
                new MouseButtonEventHandler(i_MouseRightButtonDown);

            w.MouseWheel += new MouseWheelEventHandler(w_MouseWheel);

            Application app = new Application();
            app.Run();
        }

        // The DrawPixel method updates the WriteableBitmap by using 
        // unsafe code to write a pixel into the back buffer. 
        static void DrawPixel(MouseEventArgs e)
        {
            int column = (int)e.GetPosition(i).X;
            int row = (int)e.GetPosition(i).Y;

            // Reserve the back buffer for updates.
            writeableBitmap.Lock();

            unsafe
            {
                // Get a pointer to the back buffer. 
                int pBackBuffer = (int)writeableBitmap.BackBuffer;

                // Find the address of the pixel to draw.
                pBackBuffer += row * writeableBitmap.BackBufferStride;
                pBackBuffer += column * 4;

                // Compute the pixel's color. 
                int color_data = 255 << 16; // R
                color_data |= 128 << 8;   // G
                color_data |= 255 << 0;   // B 

                // Assign the color data to the pixel.
                *((int*) pBackBuffer) = color_data;
            }

            // Specify the area of the bitmap that changed.
            writeableBitmap.AddDirtyRect(new Int32Rect(column, row, 1, 1));

            // Release the back buffer and make it available for display.
            writeableBitmap.Unlock();
        }

        static void ErasePixel(MouseEventArgs e)
        {
            byte[] ColorData = { 0, 0, 0, 0 }; // B G R

            Int32Rect rect = new Int32Rect(
                    (int)(e.GetPosition(i).X), 
                    (int)(e.GetPosition(i).Y), 
                    1, 
                    1);

            writeableBitmap.WritePixels( rect, ColorData, 4, 0);
        }

        static void i_MouseRightButtonDown(object sender, MouseButtonEventArgs e)
        {
            ErasePixel(e);
        }

        static void i_MouseLeftButtonDown(object sender, MouseButtonEventArgs e)
        {
            DrawPixel(e);
        }

        static void i_MouseMove(object sender, MouseEventArgs e)
        {
            if (e.LeftButton == MouseButtonState.Pressed)
            {
                DrawPixel(e);
            }
            else if (e.RightButton == MouseButtonState.Pressed)
            {
                ErasePixel(e);
            }
        }

        static void w_MouseWheel(object sender, MouseWheelEventArgs e)
        {
            System.Windows.Media.Matrix m = i.RenderTransform.Value;

            if (e.Delta > 0)
            {
                m.ScaleAt(
                    1.5, 
                    1.5, 
                    e.GetPosition(w).X, 
                    e.GetPosition(w).Y);
            }
            else
            {
                m.ScaleAt(
                    1.0 / 1.5, 
                    1.0 / 1.5, 
                    e.GetPosition(w).X, 
                    e.GetPosition(w).Y);
            }

            i.RenderTransform = new MatrixTransform(m);
        }
    }
}

.NET Framework

Supported in: 4.5, 4, 3.5, 3.0

.NET Framework Client Profile

Supported in: 4, 3.5 SP1

Windows 8.1, Windows Server 2012 R2, Windows 8, Windows Server 2012, Windows 7, Windows Vista SP2, Windows Server 2008 (Server Core Role not supported), Windows Server 2008 R2 (Server Core Role supported with SP1 or later; Itanium not supported)

The .NET Framework does not support all versions of every platform. For a list of the supported versions, see .NET Framework System Requirements.

Any public static (Shared in Visual Basic) members of this type are thread safe. Any instance members are not guaranteed to be thread safe.
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