Difference between revisions of "SimpleWebKit"

Revision as of 20:15, 9 April 2007

(for further editing)

originated in mySTEP
is completely written in Objective-C (1.0) so that it can be compiled on any system
aims at providing the most popular documented methods of Full WebKit for the classes WebView, WebFrame, WebDataSource, etc.
aims at rendering (X)HTML as good as possible (but not perfectly)
is work in heavy progress - so expect larger changes throughout the whole project
is used in the Vespucci.app Web Browser application for GNUstep

Features of the code in SVN trunk:

parses (X)HTML into a DOM tree
renders approx. 50% of the HTML 4.0 tags in a reasonable way (e.g. < font color="#667788">, < center>, < h2>, works)
makes <a> links clickable and processes them
is prepared to load <img>, <script> etc. and already loads them as subresources
is prepared to handle <frame>
is prepared to handle <form>
has a ECMAScript engine that parses 90% of the syntax and evaluates expressions (missing are Statements and the native Objects incl. "document", "window", "event" etc.)

Missing:

Some first screen shots (made by linking against Apple AppKit&Foundation)

1. the WebView

is the master view object and there is only one per browser (or browser tab)
it holds the mainFrame which represents either the normal <body> or the top level <frame> or <frameset>
if there is a <frameset> hierarchy, there are additional child WebFrames

2. the WebFrame

is repsonsible for loading and rendering content from a specific URL
it uses a WebDataSource to trigger loading and get callbacks
it is also the owner of the DOMDocument tree
JavaScript statements are evaluated in a frame context
it is also the target of user clicks on links since it knows the base URL (through the WebDataSource)

3. the WebDataSource

is responsible for loading data from an URL
it may cache data and handle/synchronize loading fo subresources (e.g. for an embedded <img> tag)
it translates the request and the response URLs
it provides an estimated content length (for a progress indicator) and the MIMEType of the incoming data stream
as soon as the header comes in a WebDocomentRepresentation is created and incoming segments are notified
it also collects the incoming data, so that a WebDocomentRepresentation can handle either segments or the collected data

4. the WebDocumentRepresentation(s)

there is one for each MIME type (the WebView provides a mapping database)
it is responsible for parsing the incoming data stream (either completely when finished, or partially)
and provide a better suitable representation, e.g. an NSImage or a DOMHTMLTree
finally, it creates a WebDocumentView as the child of the WebView and attaches it to the WebFrame as the -webFrameView
so, if you want to handle an additional MIME type, write a class that conforms to the WebDocumentRepresentation protocol

5. the DOMHTMLTree

is only for HTML content
is (re)built each time a new segment of HTML data comes in
any change in the DOMHTMLTree is notified to the WebDocumentView (or one of its subviews) by setNeedsLayout

6. the WebDocumentView(s) an its subviews

are responsible for displaying the contents of its WebDataRepresentation
either HTML, Images, PDF or whatever (e.g. SVG, XML, ...)
they gets notified about changes either by updates of the WebDataSource (-dadaSourceUpdated:) or directly (-setNeedsLayout:)
if one needs layout, it must go to the DOM Tree to find out what has changed and update its size, content, children, layout etc.
this is a little tricky/risky since the -layout method is called within -drawRect: - so changing e.g. the View frame is very critical and may result in drawing glitches
for HTML, we do a simple trick: the WebDocumentView is an NSTextView and the DOMHTMLTree objects can be traversed to return an attributedString with embedded Tables and NSTextAttachments

7. the JavaScript engine

is programmed according to the specificaion of [[1] ECMA-262]
uses a simple recursive stateless parser (could be optimized in stack useage and speed by a state-table driven approach)
parses the script into a Tree representation in a first step
then, evaluates the expressions and statements according to the current environement
this allows to store scripts in translated form and reevaluate them when needed (e.g. on mouse events)
uses Foundation for basic types (string, number, boolean, null)
uses WebScriptObject as the base Object representation
DOMObjects are a subclass of WebScriptObjects and therefore provide bridging, so that changing a DOMHTML tree element through JavaScript automativally triggers the appropriate WebDocumentView notification

@@ Line 78: / Line 78: @@
 . the JavaScript engine
-* is programmed according to the specificaion of ECMA-262
+* is programmed according to the specificaion of [[http://www.ecma-international.org/publications/standards/Ecma-262.htm] ECMA-262]
 * uses a simple recursive stateless parser (could be optimized in stack useage and speed by a state-table driven approach)
 * parses the script into a Tree representation in a first step