WriteableBitmap Class

Definition

Namespace:

System.Windows.Media.Imaging

Assembly:

PresentationCore.dll

Provides a BitmapSource that can be written to and updated.

public ref class WriteableBitmap sealed : System::Windows::Media::Imaging::BitmapSource

public sealed class WriteableBitmap : System.Windows.Media.Imaging.BitmapSource

type WriteableBitmap = class
    inherit BitmapSource

Public NotInheritable Class WriteableBitmap
Inherits BitmapSource

Inheritance

Object

DispatcherObject

DependencyObject

Freezable

Animatable

ImageSource

BitmapSource

WriteableBitmap

Examples

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;

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

                unsafe
                {
                    // Get a pointer to the back buffer.
                    IntPtr pBackBuffer = 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));
            }
            finally{
                // 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);
        }
    }
}

Remarks

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".

Constructors

WriteableBitmap(BitmapSource)	Initializes a new instance of the WriteableBitmap class using the given BitmapSource.
WriteableBitmap(Int32, Int32, Double, Double, PixelFormat, BitmapPalette)	Initializes a new instance of the WriteableBitmap class with the specified parameters.

Properties

BackBuffer	Gets a pointer to the back buffer.
BackBufferStride	Gets a value indicating the number of bytes in a single row of pixel data.
CanFreeze	Gets a value that indicates whether the object can be made unmodifiable. (Inherited from Freezable)
DependencyObjectType	Gets the DependencyObjectType that wraps the CLR type of this instance. (Inherited from DependencyObject)
Dispatcher	Gets the Dispatcher this DispatcherObject is associated with. (Inherited from DispatcherObject)
DpiX	Gets the horizontal dots per inch (dpi) of the image. (Inherited from BitmapSource)
DpiY	Gets the vertical dots per inch (dpi) of the image. (Inherited from BitmapSource)
Format	Gets the native PixelFormat of the bitmap data. (Inherited from BitmapSource)
HasAnimatedProperties	Gets a value that indicates whether one or more AnimationClock objects is associated with any of this object's dependency properties. (Inherited from Animatable)
Height	Gets the height of the source bitmap in device-independent units (1/96th inch per unit). (Inherited from BitmapSource)
IsDownloading	Gets a value that indicates whether the BitmapSource content is currently downloading. (Inherited from BitmapSource)
IsFrozen	Gets a value that indicates whether the object is currently modifiable. (Inherited from Freezable)
IsSealed	Gets a value that indicates whether this instance is currently sealed (read-only). (Inherited from DependencyObject)
Metadata	Gets the metadata that is associated with this bitmap image. (Inherited from BitmapSource)
Palette	Gets the color palette of the bitmap, if one is specified. (Inherited from BitmapSource)
PixelHeight	Gets the height of the bitmap in pixels. (Inherited from BitmapSource)
PixelWidth	Gets the width of the bitmap in pixels. (Inherited from BitmapSource)
Width	Gets the width of the bitmap in device-independent units (1/96th inch per unit). (Inherited from BitmapSource)

Methods

AddDirtyRect(Int32Rect)	Specifies the area of the bitmap that changed.
ApplyAnimationClock(DependencyProperty, AnimationClock, HandoffBehavior)	Applies an AnimationClock to the specified DependencyProperty. If the property is already animated, the specified HandoffBehavior is used. (Inherited from Animatable)
ApplyAnimationClock(DependencyProperty, AnimationClock)	Applies an AnimationClock to the specified DependencyProperty. If the property is already animated, the SnapshotAndReplace handoff behavior is used. (Inherited from Animatable)
BeginAnimation(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)
BeginAnimation(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)
CheckAccess()	Determines whether the calling thread has access to this DispatcherObject. (Inherited from DispatcherObject)
CheckIfSiteOfOrigin()	Checks whether the bitmap source content is from a known site of origin. This method is used to make sure that pixel copying operations are safe. (Inherited from BitmapSource)
ClearValue(DependencyProperty)	Clears the local value of a property. The property to be cleared is specified by a DependencyProperty identifier. (Inherited from DependencyObject)
ClearValue(DependencyPropertyKey)	Clears the local value of a read-only property. The property to be cleared is specified by a DependencyPropertyKey. (Inherited from DependencyObject)
Clone()	Creates 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.
CloneCore(Freezable)	Makes this instance a deep copy of the specified BitmapSource. 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. (Inherited from BitmapSource)
CloneCurrentValue()	Creates 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.
CloneCurrentValueCore(Freezable)	Makes this instance a modifiable deep copy of the specified BitmapSource using current property values. Resource references, data bindings, and animations are not copied, but their current values are. (Inherited from BitmapSource)
CoerceValue(DependencyProperty)	Coerces 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)
CopyPixels(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)
CopyPixels(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)
CopyPixels(Int32Rect, IntPtr, Int32, Int32)	Copies the bitmap pixel data within the specified rectangle. (Inherited from BitmapSource)
CreateInstance()	Initializes a new instance of the Freezable class. (Inherited from Freezable)
CreateInstanceCore()	When implemented in a derived class, creates a new instance of the Freezable derived class. (Inherited from Freezable)
Equals(Object)	Determines whether a provided DependencyObject is equivalent to the current DependencyObject. (Inherited from DependencyObject)
Freeze()	Makes the current object unmodifiable and sets its IsFrozen property to true. (Inherited from Freezable)
FreezeCore(Boolean)	Makes an instance of BitmapSource or a derived class immutable. (Inherited from BitmapSource)
GetAnimationBaseValue(DependencyProperty)	Returns the non-animated value of the specified DependencyProperty. (Inherited from Animatable)
GetAsFrozen()	Creates 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)
GetAsFrozenCore(Freezable)	Makes this instance a clone of the specified BitmapSource object. (Inherited from BitmapSource)
GetCurrentValueAsFrozen()	Creates 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)
GetCurrentValueAsFrozenCore(Freezable)	Makes this instance a frozen clone of the specified BitmapSource. Resource references, data bindings, and animations are not copied, but their current values are. (Inherited from BitmapSource)
GetHashCode()	Gets a hash code for this DependencyObject. (Inherited from DependencyObject)
GetLocalValueEnumerator()	Creates a specialized enumerator for determining which dependency properties have locally set values on this DependencyObject. (Inherited from DependencyObject)
GetType()	Gets the Type of the current instance. (Inherited from Object)
GetValue(DependencyProperty)	Returns the current effective value of a dependency property on this instance of a DependencyObject. (Inherited from DependencyObject)
InvalidateProperty(DependencyProperty)	Re-evaluates the effective value for the specified dependency property. (Inherited from DependencyObject)
Lock()	Reserves the back buffer for updates.
MemberwiseClone()	Creates a shallow copy of the current Object. (Inherited from Object)
OnChanged()	Called when the current Freezable object is modified. (Inherited from Freezable)
OnFreezablePropertyChanged(DependencyObject, DependencyObject, DependencyProperty)	This member supports the Windows Presentation Foundation (WPF) infrastructure and is not intended to be used directly from your code. (Inherited from Freezable)
OnFreezablePropertyChanged(DependencyObject, DependencyObject)	Ensures that appropriate context pointers are established for a DependencyObjectType data member that has just been set. (Inherited from Freezable)
OnPropertyChanged(DependencyPropertyChangedEventArgs)	Overrides the DependencyObject implementation of OnPropertyChanged(DependencyPropertyChangedEventArgs) to also invoke any Changed handlers in response to a changing dependency property of type Freezable. (Inherited from Freezable)
ReadLocalValue(DependencyProperty)	Returns the local value of a dependency property, if it exists. (Inherited from DependencyObject)
ReadPreamble()	Ensures that the Freezable is being accessed from a valid thread. Inheritors of Freezable must call this method at the beginning of any API that reads data members that are not dependency properties. (Inherited from Freezable)
SetCurrentValue(DependencyProperty, Object)	Sets the value of a dependency property without changing its value source. (Inherited from DependencyObject)
SetValue(DependencyProperty, Object)	Sets the local value of a dependency property, specified by its dependency property identifier. (Inherited from DependencyObject)
SetValue(DependencyPropertyKey, Object)	Sets the local value of a read-only dependency property, specified by the DependencyPropertyKey identifier of the dependency property. (Inherited from DependencyObject)
ShouldSerializeProperty(DependencyProperty)	Returns a value that indicates whether serialization processes should serialize the value for the provided dependency property. (Inherited from DependencyObject)
ToString()	Creates a string representation of this object based on the current culture. (Inherited from ImageSource)
ToString(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)
TryLock(Duration)	Attempts to lock the bitmap, waiting for no longer than the specified length of time.
Unlock()	Releases the back buffer to make it available for display.
VerifyAccess()	Enforces that the calling thread has access to this DispatcherObject. (Inherited from DispatcherObject)
WritePixels(Int32Rect, Array, Int32, Int32, Int32)	Updates the pixels in the specified region of the bitmap.
WritePixels(Int32Rect, Array, Int32, Int32)	Updates the pixels in the specified region of the bitmap.
WritePixels(Int32Rect, IntPtr, Int32, Int32, Int32, Int32)	Updates the pixels in the specified region of the bitmap.
WritePixels(Int32Rect, IntPtr, Int32, Int32)	Updates the pixels in the specified region of the bitmap.
WritePostscript()	Raises the Changed event for the Freezable and invokes its OnChanged() method. Classes that derive from Freezable should call this method at the end of any API that modifies class members that are not stored as dependency properties. (Inherited from Freezable)
WritePreamble()	Verifies that the Freezable is not frozen and that it is being accessed from a valid threading context. Freezable inheritors should call this method at the beginning of any API that writes to data members that are not dependency properties. (Inherited from Freezable)

Events

Changed	Occurs when the Freezable or an object it contains is modified. (Inherited from Freezable)
DecodeFailed	Occurs when the image fails to load, due to a corrupt image header. (Inherited from BitmapSource)
DownloadCompleted	Occurs when the bitmap content has been completely downloaded. (Inherited from BitmapSource)
DownloadFailed	Occurs when the bitmap content failed to download. (Inherited from BitmapSource)
DownloadProgress	Occurs when the download progress of the bitmap content has changed. (Inherited from BitmapSource)

Explicit Interface Implementations

IFormattable.ToString(String, IFormatProvider)

Formats the value of the current instance using the specified format. (Inherited from ImageSource)

See also

• BitmapSource