Table of Contents

Class Canvas

Namespace
iText.Layout
Assembly
itext.layout.dll

This class is used for adding content directly onto a specified PdfCanvas.

public class Canvas : RootElement<Canvas>, IPropertyContainer, IDisposable
Inheritance
Canvas
Implements
Inherited Members

Remarks

This class is used for adding content directly onto a specified PdfCanvas. Canvas does not know the concept of a page, so it can't reflow to a 'next' Canvas. This class effectively acts as a bridge between the high-level layout API and the low-level kernel API.

Constructors

Canvas(PdfCanvas, Rectangle)

Creates a new Canvas to manipulate a specific content stream, which might be for example a page or PdfFormXObject stream.

public Canvas(PdfCanvas pdfCanvas, Rectangle rootArea)

Parameters

pdfCanvas PdfCanvas

the low-level content stream writer

rootArea Rectangle

the maximum area that the Canvas may write upon

Canvas(PdfCanvas, Rectangle, bool)

Creates a new Canvas to manipulate a specific document and page.

public Canvas(PdfCanvas pdfCanvas, Rectangle rootArea, bool immediateFlush)

Parameters

pdfCanvas PdfCanvas

The low-level content stream writer

rootArea Rectangle

The maximum area that the Canvas may write upon

immediateFlush bool

Whether to flush the canvas immediately after operations, false otherwise

Canvas(PdfPage, Rectangle)

Creates a new Canvas to manipulate a specific page content stream.

public Canvas(PdfPage page, Rectangle rootArea)

Parameters

page PdfPage

the page on which this canvas will be rendered, shall not be flushed (see IsFlushed() ).

rootArea Rectangle

the maximum area that the Canvas may write upon

Remarks

Creates a new Canvas to manipulate a specific page content stream. The given page shall not be flushed: drawing on flushed pages is impossible because their content is already written to the output stream. Use this constructor to be able to add Link elements on it (using any other constructor would result in inability to add PDF annotations, based on which, for example, links work).

If the IsTagged() is true, using this constructor would automatically enable the tagging for the content. Regarding tagging the effect is the same as using EnableAutoTagging(PdfPage).

Canvas(PdfFormXObject, PdfDocument)

Creates a new Canvas to manipulate a specific PdfFormXObject.

public Canvas(PdfFormXObject formXObject, PdfDocument pdfDocument)

Parameters

formXObject PdfFormXObject

the form

pdfDocument PdfDocument

the document that the resulting content stream will be written to

Fields

page

Is initialized and used only when Canvas element autotagging is enabled, see EnableAutoTagging(PdfPage).

protected PdfPage page

Field Value

PdfPage

Remarks

Is initialized and used only when Canvas element autotagging is enabled, see EnableAutoTagging(PdfPage). It is also used to determine if autotagging is enabled.

pdfCanvas 

protected PdfCanvas pdfCanvas

Field Value

PdfCanvas

rootArea 

protected Rectangle rootArea

Field Value

Rectangle

Methods

Close()

Closes the Canvas.

public override void Close()

Remarks

Closes the Canvas . Although not completely necessary in all cases, it is still recommended to call this method when you are done working with Canvas object, as due to some properties set there might be some 'hanging' elements, which are waiting other elements to be added and processed. Close() tells the Canvas that no more elements will be added and it is time to finish processing all the elements.

EnableAutoTagging(PdfPage)

Enables canvas content autotagging.

public virtual void EnableAutoTagging(PdfPage page)

Parameters

page PdfPage

the page, on which this canvas will be rendered.

Remarks

Enables canvas content autotagging. By default it is disabled.

EnsureRootRendererNotNull() 

protected override RootRenderer EnsureRootRendererNotNull()

Returns

RootRenderer

Flush()

Forces all registered renderers (including child element renderers) to flush their contents to the content stream.

public virtual void Flush()

GetPage()

The page on which this canvas will be rendered.

public virtual PdfPage GetPage()

Returns

PdfPage

the specified PdfPage instance, might be null if this the page was not set.

GetPdfCanvas()

Gets the PdfCanvas.

public virtual PdfCanvas GetPdfCanvas()

Returns

PdfCanvas

the low-level content stream writer

GetPdfDocument()

Gets the PdfDocument for this canvas.

public virtual PdfDocument GetPdfDocument()

Returns

PdfDocument

the document that the resulting content stream will be written to

GetRootArea()

Gets the root area rectangle.

public virtual Rectangle GetRootArea()

Returns

Rectangle

the maximum area that the Canvas may write upon

IsAutoTaggingEnabled() 

public virtual bool IsAutoTaggingEnabled()

Returns

bool

true if autotagging of canvas content is enabled. Default value - false.

IsCanvasOfPage()

Defines if the canvas is exactly the direct content of the page.

public virtual bool IsCanvasOfPage()

Returns

bool

true if the canvas on which this instance performs drawing is directly the canvas of the page; false if the instance of this class was created not with Canvas(PdfPage, Rectangle) constructor overload.

Remarks

Defines if the canvas is exactly the direct content of the page. This is known definitely only if this instance was created by Canvas(PdfPage, Rectangle) constructor overload, otherwise this method returns false.

Relayout()

Performs an entire recalculation of the element flow on the canvas, taking into account all its current child elements.

public virtual void Relayout()

Remarks

Performs an entire recalculation of the element flow on the canvas, taking into account all its current child elements. May become very resource-intensive for large documents. Do not use when you have set immediateFlush to true.

SetRenderer(CanvasRenderer)

Sets the IRenderer for this Canvas.

public virtual void SetRenderer(CanvasRenderer canvasRenderer)

Parameters

canvasRenderer CanvasRenderer

a renderer specific for canvas operations