Wt  3.3.0
Public Member Functions | Protected Member Functions
Wt::WRasterImage Class Reference

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

#include <Wt/WRasterImage>

Inheritance diagram for Wt::WRasterImage:
Inheritance graph
[legend]

List of all members.

Public Member Functions

 WRasterImage (const std::string &type, const WLength &width, const WLength &height, WObject *parent=0)
 Creates a raster image.
 ~WRasterImage ()
 Destructor.
void addFontCollection (const std::string &directory, bool recursive=true)
 Adds a font collection.
virtual WFlags< FeatureFlagfeatures () const
 Returns device features.
virtual void setChanged (WFlags< ChangeFlag > flags)
 Indicates changes in painter state.
virtual void drawArc (const WRectF &rect, double startAngle, double spanAngle)
 Draws an arc.
virtual void drawImage (const WRectF &rect, const std::string &imgUri, int imgWidth, int imgHeight, const WRectF &sourceRect)
 Draws an image.
virtual void drawLine (double x1, double y1, double x2, double y2)
 Draws a line.
virtual void drawPath (const WPainterPath &path)
 Draws a path.
virtual void drawText (const WRectF &rect, WFlags< AlignmentFlag > alignmentFlags, TextFlag textFlag, const WString &text)
 Draws text.
virtual WTextItem measureText (const WString &text, double maxWidth=-1, bool wordWrap=false)
 Measures rendered text size.
virtual WFontMetrics fontMetrics ()
 Returns font metrics.
virtual void init ()
 Initializes the device for painting.
virtual void done ()
 Finishes painting on the device.
virtual bool paintActive () const
 Returns whether painting is active.
virtual WLength width () const
 Returns the device width.
virtual WLength height () const
 Returns the device height.
virtual void handleRequest (const Http::Request &request, Http::Response &response)
 Handles a request.
void setPixel (int x, int y, const WColor &color)
 Low-level paint method.
WColor getPixel (int x, int y)
 Low-level paint method.
void clear ()
 Clears the image.

Protected Member Functions

virtual WPainterpainter () const
 Returns the painter that is currently painting on the device.
virtual void setPainter (WPainter *painter)
 Sets the painter.

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:

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. If Wt is built to use libpango for font support, then text rendering is done using this library. Otherwise, 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:


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.

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 is defined as in WPainter::drawArc(const WRectF& rectangle, int startAngle, int spanAngle)

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 
) [virtual]

Draws text.

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

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::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.

See also:
init(), painter()

Implements Wt::WPaintDevice.

virtual WPainter* Wt::WRasterImage::painter ( ) const [protected, virtual]

Returns the painter that is currently painting on the device.

See also:
init()

Implements Wt::WPaintDevice.

void Wt::WRasterImage::setChanged ( WFlags< ChangeFlag flags) [virtual]

Indicates changes in painter state.

The flags argument is the logical OR of one or more change flags.

See also:
ChangeFlag

Implements Wt::WPaintDevice.

void Wt::WRasterImage::setPixel ( int  x,
int  y,
const WColor color 
)

Low-level paint method.

Use this method to directly set colors for individual pixels, when using the paint device without a painter.

virtual WLength Wt::WRasterImage::width ( ) const [virtual]

Returns the device width.

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

Implements Wt::WPaintDevice.

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