A paint device for rendering to a raster image. More...

#include <Wt/WRasterImage>

Inheritance diagram for Wt::WRasterImage:

Public Member Functions
	WRasterImage (const std::string &type, const WLength &width, const WLength &height, WObject *parent=0)
	Creates a raster image. More...

	~WRasterImage ()
	Destructor.

void	addFontCollection (const std::string &directory, bool recursive=true)
	Adds a font collection. More...

virtual WFlags< FeatureFlag >	features () const
	Returns device features.

virtual void	setChanged (WFlags< ChangeFlag > flags)
	Indicates changes in painter state. More...

virtual void	drawArc (const WRectF &rect, double startAngle, double spanAngle)
	Draws an arc. More...

virtual void	drawImage (const WRectF &rect, const std::string &imgUri, int imgWidth, int imgHeight, const WRectF &sourceRect)
	Draws an image. More...

virtual void	drawLine (double x1, double y1, double x2, double y2)
	Draws a line. More...

virtual void	drawPath (const WPainterPath &path)
	Draws a path. More...

virtual void	drawText (const WRectF &rect, WFlags< AlignmentFlag > alignmentFlags, TextFlag textFlag, const WString &text, const WPointF *clipPoint)
	Draws text. More...

virtual WTextItem	measureText (const WString &text, double maxWidth=-1, bool wordWrap=false)
	Measures rendered text size. More...

virtual WFontMetrics	fontMetrics ()
	Returns font metrics. More...

virtual void	init ()
	Initializes the device for painting. More...

virtual void	done ()
	Finishes painting on the device. More...

virtual bool	paintActive () const
	Returns whether painting is active. More...

virtual WLength	width () const
	Returns the device width. More...

virtual WLength	height () const
	Returns the device height. More...

virtual void	handleRequest (const Http::Request &request, Http::Response &response)
	Handles a request. More...

void	setPixel (int x, int y, const WColor &color)
	Low-level paint method. More...

WColor	getPixel (int x, int y)
	Low-level paint method. More...

void	getPixels (void *data)
	Low-level pixel retrieval. More...

void	clear ()
	Clears the image. More...

Public Member Functions inherited from Wt::WResource
	WResource (WObject *parent=0)
	Creates a new resource.

	~WResource ()
	Destroys the resource. More...

void	suggestFileName (const Wt::WString &name, DispositionType dispositionType=Attachment)
	Suggests a filename to the user for the data streamed by this resource. More...

const Wt::WString &	suggestedFileName () const
	Returns the suggested file name. More...

void	setDispositionType (DispositionType cd)
	Configures the Content-Disposition header. More...

DispositionType	dispositionType () const
	Returns the currently configured content disposition. More...

void	setChanged ()
	Generates a new URL for this resource and emits the changed signal. More...

void	setInternalPath (const std::string &path)
	Sets an internal path for this resource. More...

std::string	internalPath () const
	Returns the internal path. More...

const std::string &	generateUrl ()
	Generates an URL for this resource. More...

const std::string &	url () const
	Returns the current URL for this resource. More...

Signal &	dataChanged ()
	Signal emitted when the data presented in this resource has changed. More...

void	setUploadProgress (bool enabled)
	Indicate interest in upload progress. More...

Signal< ::uint64_t,::uint64_t > &	dataReceived ()
	Signal emitted when data has been received for this resource. More...

void	write (std::ostream &out, const Http::ParameterMap &parameters=Http::ParameterMap(), const Http::UploadedFileMap &files=Http::UploadedFileMap())
	Stream the resource to a stream. More...

virtual void	handleAbort (const Http::Request &request)
	Handles a continued request being aborted. More...

void	haveMoreData ()
	Indicate that more data is available. More...

Public Member Functions inherited from Wt::WObject
	WObject (WObject *parent=0)
	Create a WObject with a given parent object. More...

virtual	~WObject ()
	Destructor. More...

virtual const std::string	id () const
	Returns the (unique) identifier for this object. More...

virtual void	setObjectName (const std::string &name)
	Sets an object name. More...

virtual std::string	objectName () const
	Returns the object name. More...

void	resetLearnedSlots ()
	Resets learned stateless slot implementations. More...

template<class T >
void	resetLearnedSlot (void(T::*method)())
	Resets a learned stateless slot implementation. More...

template<class T >
WStatelessSlot *	implementStateless (void(T::*method)())
	Declares a slot to be stateless and learn client-side behaviour on first invocation. More...

template<class T >
WStatelessSlot *	implementStateless (void(T::method)(), void(T::undoMethod)())
	Declares a slot to be stateless and learn client-side behaviour in advance. More...

void	isNotStateless ()
	Marks the current function as not stateless. More...

template<class T >
WStatelessSlot *	implementJavaScript (void(T::*method)(), const std::string &jsCode)
	Provides a JavaScript implementation for a method. More...

void	addChild (WObject *child)
	Adds a child object. More...

virtual void	removeChild (WObject *child)
	Removes a child object. More...

const std::vector< WObject * > &	children () const
	Returns the children.

WObject *	parent () const
	Returns the parent object.

Public Member Functions inherited from Wt::WPaintDevice
virtual	~WPaintDevice ()
	Destructor. More...

Protected Member Functions
virtual WPainter *	painter () const
	Returns the painter that is currently painting on the device. More...

virtual void	setPainter (WPainter *painter)
	Sets the painter.

Protected Member Functions inherited from Wt::WResource
void	beingDeleted ()
	Prepares the resource for deletion. More...

Protected Member Functions inherited from Wt::WObject
virtual WStatelessSlot *	getStateless (Method method)
	On-demand stateless slot implementation. More...

Additional Inherited Members
Public Types inherited from Wt::WResource
Public Types inherited from Wt::WObject
typedef void(WObject::*	Method) ()
	Typedef for a WObject method without arguments.

Public Types inherited from Wt::WPaintDevice
Static Protected Member Functions inherited from Wt::WObject
static WObject *	sender ()
	Returns the sender of the current slot call. More...

Detailed Description

A paint device for rendering to a raster image.

A WRasterImage paint device provides support for creating raster images (such as PNG or GIF images).

It implements two main use-cases:

When used either in conjunction with a WPainter, it supports vector graphics operations, and can be used to make a PNG or GIF version of a WPaintedWidget's contents.
It also provides a low-level API to color individual pixels using setPixel(), which directly sets the raster pixels.

On Linux, the rendering is provided by GraphicsMagick, and this class is included in the library only if libgraphicsmagick was found during the build of the library. As an alternative, Wt supports certain versions of skia. In general skia is a good and performant renderer, but since it does not have releases, and a not very stable API, we don't recommend it. On Windows, Direct2D is used for rendering, which means that no extra dependencies have to be installed.

If Wt is built to use libpango for font support, then text rendering is done using this library. On Windows, DirectWrite is used for font support functions. In other cases, you may want to configure TrueType font search directories using addFontCollection().

You can use the image as a resource and specialize handleRequest() to paint the contents on the fly. Alternatively can also use write() to serialize to an image file (std::ostream).

The latter usage is illustrated by the code below:

Wt::Chart::WCartesianChart *chart = ...
Wt::WRasterImage pngImage("png", 600, 400);
{
  Wt::WPainter p(&pngImage);
  chart->paint(p);
}
std::ofstream f("chart.png", std::ios::out | std::ios::binary);
pngImage.write(f);

This paint device has the following limitations:

drop shadows are (not yet?) supported.

Constructor & Destructor Documentation

Wt::WRasterImage::WRasterImage	(	const std::string &	type,
		const WLength &	width,
		const WLength &	height,
		WObject *	parent = `0`
	)

Creates a raster image.

type indicates an image type. The mime type of the resource is "image/" type.

Wt supports the following image types (amongst others):

png: Portable Network Graphics
gif: Graphics Interchange Format
bmp: Microsoft windows bitmap
jpeg: Joint Photographic Experts Group JFIF format

Member Function Documentation

void Wt::WRasterImage::addFontCollection	(	const std::string &	directory,
		bool	recursive = `true`
	)

Adds a font collection.

If Wt has been configured to use libpango, then font matching and character selection is done by libpango, which is seeded with information on installed fonts by fontconfig. In that case, invocations for this method is ignored.

If Wt has not been configured to use libpango, then this method may be used to indicate the location of true type fonts. The main drawback compared to libpango is that font selection is not steered by the need for particular characters, i.e. font selection is independent from the text's need for specific characters. Most truetype fonts provided only partial unicode support. The provided directory will be searched for fonts (currently only TrueType ".ttf" or ".ttc" fonts).

void Wt::WRasterImage::clear ( )

Clears the image.

Fills the image with a white background, or transparent if possible.

void Wt::WRasterImage::done ( )

virtual

Finishes painting on the device.

This method is called when a WPainter stopped painting.

See also: WPainter::end()

Implements Wt::WPaintDevice.

void Wt::WRasterImage::drawArc	(	const WRectF &	rect,
		double	startAngle,
		double	spanAngle
	)

virtual

Draws an arc.

The arc describes the segment of an ellipse enclosed by the rect. The segment starts at startAngle, and spans an angle given by spanAngle. These angles have as unit degree, and are measured counter-clockwise starting from the 3 o'clock position.

The arc must be stroked, filled, and transformed using the current painter settings.

Implements Wt::WPaintDevice.

void Wt::WRasterImage::drawImage	(	const WRectF &	rect,
		const std::string &	imageUri,
		int	imgWidth,
		int	imgHeight,
		const WRectF &	sourceRect
	)

virtual

Draws an image.

Draws sourceRect from the image with URL imageUri and original dimensions imgWidth and imgHeight to the location, into the rectangle defined by rect.

The image is transformed using the current painter settings.

Implements Wt::WPaintDevice.

void Wt::WRasterImage::drawLine	(	double	x1,
		double	y1,
		double	x2,
		double	y2
	)

virtual

Draws a line.

The line must be stroked and transformed using the current painter settings.

Implements Wt::WPaintDevice.

void Wt::WRasterImage::drawPath ( const WPainterPath & path )

virtual

Draws a path.

The path must be stroked, filled, and transformed using the current painter settings.

Implements Wt::WPaintDevice.

void Wt::WRasterImage::drawText	(	const WRectF &	rect,
		WFlags< AlignmentFlag >	alignmentFlags,
		TextFlag	textFlag,
		const WString &	text,
		const WPointF *	clipPoint
	)

virtual

Draws text.

The text must be rendered, stroked and transformed using the current painter settings.

If clipPoint is not null, a check is performed whether the point is inside of the current clip area. If not, the text is not drawn.

Implements Wt::WPaintDevice.

WFontMetrics Wt::WRasterImage::fontMetrics ( )

virtual

Returns font metrics.

This returns font metrics for the current font.

Throws a std::logic_error if the underlying device does not provide font metrics.

Implements Wt::WPaintDevice.

WColor Wt::WRasterImage::getPixel	(	int	x,
		int	y
	)

Low-level paint method.

Use this method to directly get the color for an individual pixel, when using the paint device without a painter.

void Wt::WRasterImage::getPixels ( void * data )

Low-level pixel retrieval.

This is a more efficient alternative than calling getPixel() for every pixel.

Parameter data must point to an allocated memory region of width*height 32-bit words. The pixels will be written in row-order from top-left to bottom-right, in RGBA format.

void Wt::WRasterImage::handleRequest	(	const Http::Request &	request,
		Http::Response &	response
	)

virtual

Handles a request.

Reimplement this method so that a proper response is generated for the given request. From the request object you can access request parameters and whether the request is a continuation request. In the response object, you should set the mime type and stream the output data.

A request may also concern a continuation, indicated in Http::Request::continuation(), in which case the next part for a previously created continuation should be served.

While handling a request, which may happen at any time together with event handling, the library makes sure that the resource is not being concurrently deleted, but multiple requests may happend simultaneously for a single resource.

Implements Wt::WResource.

virtual WLength Wt::WRasterImage::height ( ) const

virtual

Returns the device height.

The device height, in pixels, establishes the height of the device coordinate system.

Implements Wt::WPaintDevice.

void Wt::WRasterImage::init ( )

virtual

Initializes the device for painting.

This method is called when a WPainter starts painting.

See also: WPainter::begin(WPaintDevice *), painter()

Implements Wt::WPaintDevice.

WTextItem Wt::WRasterImage::measureText	(	const WString &	text,
		double	maxWidth = `-1`,
		bool	wordWrap = `false`
	)

virtual

Measures rendered text size.

Returns the bounding rect of the given text when rendered using the current font.

If maxWidth != -1, then the text is truncated to fit in the width.

If wordWrap = true then text is truncated only at word boundaries. Note that in this case the whitespace at the truncated position is included in the text but not accounted for by the returned width (since usually you will not render the whitespace at the end of a line).

Throws a std::logic_error if the underlying device does not provide font metrics.

Implements Wt::WPaintDevice.

virtual bool Wt::WRasterImage::paintActive ( ) const

virtual

Returns whether painting is active.