org.gwtwidgets.client.ui.canvas.impl
Class BitmapFontImpl

java.lang.Object
  org.gwtwidgets.client.ui.canvas.Font
      org.gwtwidgets.client.ui.canvas.impl.BitmapFontImpl

All Implemented Interfaces:

com.google.gwt.http.client.RequestCallback

Direct Known Subclasses:

CanvasBackedBitmapFontImpl

public class BitmapFontImpl
extends Font
implements com.google.gwt.http.client.RequestCallback

A BitmapFontImpl object encapsulates a font and knows how to draw text on a canvas. This base implementation renders bitmap fonts read from an image and a font descriptor.

The font is usually not usable right after instantiation because asynchronous requests are made towards the server in order to retrieve font specific information. If required, load listeners can be attached to the font object in order to poll its load status.

BitmapFontImpl objects are expensive to create and maintain as two requests are made to the server for the font bitmap and the font descriptor, the entire bitmap is stored in the browser's cache and a costly parsing of the font descriptor is performed.

Author:

George Georgovassilis g.georgovassilis[at]gmail.com

Field Summary

protected com.google.gwt.user.client.Element	bitmap
protected int	blockHeight
protected java.util.Map	characters
protected boolean	descriptionLoaded
protected boolean	imageLoaded
protected FontLoadListener	listener

Constructor Summary

BitmapFontImpl(java.lang.String bitmapPath, java.lang.String descriptionPath, FontLoadListener listener)
Constructs a canvas font and loads required resources from the server.

Method Summary

protected FontLoadListener	doWithListener(FontLoadListener listener) Allows substitution of a listener in the constructor of extending classes
protected void	drawGlyph(char c, Canvas canvas, double charOffsetLeft, double charOffsetTop, double charWidth, double blockHeight, double destinationX, double destinationY, double destinationWidth, double destinationHeight) Draws a character.
void	drawText(java.lang.String text, Canvas canvas, double x, double y)
void	onError(com.google.gwt.http.client.Request request, java.lang.Throwable exception)
void	onResponseReceived(com.google.gwt.http.client.Request request, com.google.gwt.http.client.Response response)

Methods inherited from class java.lang.Object

clone, equals, finalize, getClass, hashCode, notify, notifyAll, toString, wait, wait, wait

Field Detail

characters

protected java.util.Map characters

blockHeight

protected int blockHeight

imageLoaded

protected boolean imageLoaded

descriptionLoaded

protected boolean descriptionLoaded

listener

protected FontLoadListener listener

bitmap

protected com.google.gwt.user.client.Element bitmap

Constructor Detail

BitmapFontImpl

public BitmapFontImpl(java.lang.String bitmapPath,
                      java.lang.String descriptionPath,
                      FontLoadListener listener)

Constructs a canvas font and loads required resources from the server. This method will issue two HTTP requests to the server:

• A request for reading the bitmap representation of the font. A relative request is made to bitmapPath to retrieve the font bitmap as created by the BitmapFontCreator
• The font descriptor is retrieved by a request to descriptionPath

Parameters:

bitmapPath - URL to the bitmap containing the font's graphical representation.

descriptionPath - URL to the font's descriptor.

listener - Optional listener to execute when the font is ready to use. Can be null.

token - Token to be passed to the listener

Method Detail

doWithListener

protected FontLoadListener doWithListener(FontLoadListener listener)

Allows substitution of a listener in the constructor of extending classes

Parameters:

listener -

Returns:

drawGlyph

protected void drawGlyph(char c,
                         Canvas canvas,
                         double charOffsetLeft,
                         double charOffsetTop,
                         double charWidth,
                         double blockHeight,
                         double destinationX,
                         double destinationY,
                         double destinationWidth,
                         double destinationHeight)

Draws a character. Invoked by drawText(String, Canvas, double, double). Can be overridden by extending implementations.

Parameters:

c - Character to draw

canvas - Canvas to draw on

charOffsetLeft - Horizontal character offset on the template bitmap

charOffsetTop - Vertical character offset on the template bitmap

charWidth - Glyph width

blockHeight - Glyph height

destinationX - Destination X on canvas

destinationY - Destination Y on canvas

destinationWidth - Width of character to draw

destinationHeight - Height of character to draw

drawText

public void drawText(java.lang.String text,
                     Canvas canvas,
                     double x,
                     double y)

Specified by:

drawText in class Font

onError

public void onError(com.google.gwt.http.client.Request request,
                    java.lang.Throwable exception)

Specified by:

onError in interface com.google.gwt.http.client.RequestCallback

onResponseReceived

public void onResponseReceived(com.google.gwt.http.client.Request request,
                               com.google.gwt.http.client.Response response)

Specified by:

onResponseReceived in interface com.google.gwt.http.client.RequestCallback