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383 строки
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<title>GFX2 Proposal</title>
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<div class="title">
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<h1>GFX2: The widget/gfx redesign</h1>
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"GFX2" provides what is currently provided by both gfx and widget (including timers).
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</div>
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<hr/>
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<h2>Problems with the current implementations:</h2>
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<div>
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<h3>Graphics</h3>
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<div><ul>
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<li>Performance
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<div><p>Due to some of the current APIs, it is hard for us to fully leverage an operating
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system graphics capabilities. The advantage to using the OS facilities is that
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they are often optimized for their specific processor and/or video hardware
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architectures.</p>
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<p>An example of this approach is the Apple Quartz graphics architecture which
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provides the next generation graphics capabilities behind the Aqua user interface.
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All of MacOS X's graphics APIs are accelerated for their Altivec/Velocity
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engine enabled processors and push graphic operations to accelerated video
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hardware whenever possible.</p></div>
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</li>
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<li>Alpha Channel Compositing
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<div><ul>
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<li>The current alpha blending code doesn't support all bitdepths.</li>
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<li>We need a view for each alpha blended pixmap.<strong>??</strong></li>
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<li>We cannot take advantage of any accelerated OS blending code.</li>
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</ul></div>
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</li>
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<li>Clipping
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<div>We currently do far too much clipping. This causes numerous performance problems,
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especially on X11 based systems. Due to the way X works, changing the clip
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region makes the X server have to flush its connections to make sure nothing
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has changed since it received the clip region. <strong>(this isn't a completely
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accurate description, change it)</strong>
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<p>This should help Windows as well.</p>
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</div>
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</li>
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<li>Images
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<div><ul>
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<li>Memory Footprint
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<div>Currently, we keep at least two copies of the image data around in memory.
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One compressed and one decompressed. As part of GFX2 and imagelib 1.5,we
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hope to only hold a single copy of the image data in memory.</div>
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</li>
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<li>Scaling and Dithering
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<div>Both image scaling and dithering currently is done in both imagelib and gfx
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depending on your platform and the code path that layout uses to draw the
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image. This causes confusion and does not allow the platform to optimize the
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scaling and dithering operations.</div>
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</li>
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<li>Image Color Correction
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<div>We don't have it today. Apple has been working on ColorSync integration that is not complete and doesn't
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provide a solution for Linux and Windows. This prevented PNGs from being used in the modern 2 skin.</div>
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</li>
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</ul></div>
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</li>
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<li>Spacial Graphics Independence
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<div>Twips are the device independent units that we theoretically use to achieve
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WYSIWYG printing and cross display rendering. The disadvantage to the current
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approach is that we have to convert from pixels to twips coming into the system,
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and back again to pixels whenever we go out to the display device. This is a performance hit and
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causes confusion in the code.</div>
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</li>
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<li>SVG (Scaleable Vector Graphics)
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<div>The current graphics APIs that we have do not provide support for rendering
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vector graphics. There is no clean way to add these drawing primitives
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to the current gfx APIs. Scaled vector graphics operations also lend themselves
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to hardware acceleration which any implementation cannot cleanly utilize
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in an XP manor.</div>
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</li>
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</ul></div>
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<h3>Widgets</h3>
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<div>
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Many of the APIs were designed for when we had native widgets.
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<div><ul>
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<li>Events
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<div>The way operating systems handle events are often quite different. This
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creates a problem with the current way we handle events. Engineers are
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forced to spend large amounts of time tracking down bugs that are caused
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by event ordering, and with no solid specification on how we should send
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events, this problem will continue.</div>
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</li>
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<li>Native form controls
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<div>There is good bit of code left in the current widget module that is no
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longer used or needed. These interfaces and code should be removed. Should
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the need for "native" form controls arise again, XBL should be able to
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do the job of making native looking and feeling form controls or wrapping native
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control implementations.</div>
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</li>
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<li>UNIX Toolkit
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<div>The use of GTK introduces a little bit of extra memory footprint that is
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no longer needed since we no longer use native widgets.</div>
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</li>
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</ul></div>
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</div>
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</div>
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<hr/>
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<h2>Proposal:</h2>
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<div>
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<ul>
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<li>Merge widget (including timers) and gfx in to a single component
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Since both widget and gfx deal with the native OS, drawing, and events,
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there is no reason for them to be separate components. This will reduce
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cross library calls in critical code paths and centralize native code.</li>
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<li><h3>Graphics</h3>
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<div><ul>
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<li>Performance</li>
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<li>Alpha Channel Compositing</li>
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<li>Clipping
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<div>Potentially add mandatory vs. discretionary clip regions.
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Robert O'Calahan has been thinking about these issues. <strong>need info</strong></div>
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</li>
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<li>Images
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<div><ul>
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<li>Memory Footprint
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<div><strong>...?</strong></div>
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</li>
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<li>Imglib1.5
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<div><a href="mailto:tor@cs.brown.edu">Tim Rowley</a> is working on imglib 1.5.
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The new image library in conjunction with the new imaging APIs in GFX2,
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we should be able to reduce the number of copies of the image data to one.</div>
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</li>
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<li>Scaling and dithering
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<div>As part of imglib 1.5, Tim will be removing imglib's image scaling and
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dithering code. All image data will come from imglib as 32bit RGBA packed image data.
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Each platform's GFX2 implementation may decide what bit depth to cache the
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data in. Each GFX2 implementation must be able to scale an image using either native
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system APIs or another means. Having each platform do this allows platforms
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that do support scaling and/or dithering to take advantage of any hardware
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optimizations that they can. nsIDrawable provides separate methods for drawing
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an image and drawing a scaled image to avoid any confusion about how to
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draw an image. Platforms that do not support scaling or dithering could port gdkrgb
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and/or gdk_pixbuf to their platform to provide these
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services in software for them.</div>
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</li>
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<li>Image Color Correction
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<div>We want to support this. <strong>needs investigation</strong></div>
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</li>
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</ul></div>
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</li>
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<li>Spacial Graphics Independence
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<div>Remove twips from the common code paths. With the CPUs used in modern hardware,
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we can replace twips with floating point pixel based coordinates and dimensions. Using
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floating point aims to reduce the potential rounding errors to one final coordinate
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system to device conversion. For systems without a FPU (StrongArm, etc),
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<a href="mailto:scc@mozilla.org">Scott Collins</a> has volunteered to write a fixed-point
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class that we could simply plug in instead of floating points. Devices such as printers
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would be able to use a transformation matrix to scale the pixel values so that
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they match the DPI that you are printing to.</div>
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</li>
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<li>SVG (Scaleable Vector Graphics)
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<div><ul>
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<li>Interfaces
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<div>SVG related drawing methods will be put on their own interface, something
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like nsIVectorDrawable, which you can QI to and from an nsIDrawable. An
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XP implementation that does its own rasterization and delegates everything
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else to an underlying GFX implementation is needed to do this.</p>
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</div>
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</li>
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<li>People
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<div><a href="mailto:kmcclusk@netscape.com">Kevin McCluskey</a> is on the SVG working group.
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<strong>need to get input from him</strong>
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</div>
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</li>
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<li>Cross-platform Solutions
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<div><ul>
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<li>Fonts
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<div><a href="http://www.freetype.org/">FreeType</a> is a high-quality font
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rendering engine capable of rendering anti-aliased fonts as well as rotating
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them where the OS is not sufficient.</div>
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</li>
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<li>Drawing
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<div><a href="http://www.artofcode.com/libart.html">libart</a> is a library
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designed to render curves, vectors, do alpha compositing, etc. Unfortunately
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the author no longer has much time to work on it, so we would need someone
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here to work on it and integrate it with our system, again where OS facilities
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are not present or appropriate. <a href="mailto:alexl@redhat.com">Alex Larson</a> has worked on libart
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in the past and can provide assistance.</div>
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</li>
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</ul></div>
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</li>
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</ul></div>
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</li>
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</ul></div>
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</li>
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<li><h3>Widgets</h3>
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<div><ul>
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<li>Events
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<div>As part of GFX2, the events generated by the system will have to conform
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to a specification that will be written up by <a href="mailto:pavlov@netscape.com">Stuart
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Parmenter</a>, <a href="mailto:joki@netscape.com">Tom Pixley</a>, <a href="mailto:saari@netscape.com">Chris
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Saari</a>, and others. This will ensure that all events received by listeners
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to windows will receive them in a cross platform manner and help to remove
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numerous problems that we currently have in this area. A test listener suite
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should be made that validates a platform implementation to ensure that
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it meets the specification perfectly.</div>
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</li>
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<li>Native Form Controls
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<div>XBL can be used to do this work with less overhead and problems than using
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real native widgets. For example, Internet Explorer on Windows does not use win32 native
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form controls. Currently there is no need for native form controls, but
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this could change. The APIs have been designed so that native form controls
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and other native widgets may be added later without disrupting the current
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set of GFX2 APIs.</div>
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</li>
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<li>UNIX Toolkit
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<div>Since we no longer need native widgets, we can remove the dependencies on
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Unix build dependencies on GTK which will reduce build dependencies and reduce some
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memory footprint by only depending on Xlib.</div>
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</li>
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</ul></div>
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</li>
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<li><h3>System Services</h3>
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<div><ul>
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<li>Clipboard
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<div>The clipboard interfaces remain mostly the same. There has been discussion
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about making the getData methods asynchronous, but nothing has been finalized
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at this time.</div>
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</li>
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<li>Drag and Drop
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<div>At the time of this writing, the drag and drop interfaces have not been
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looked at, but they are not expected to change a great deal.</div>
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</li>
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<li>File Picker
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<div>The file picker interface has not changed. There has been talk of changing
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the way filtering works a bit, but this has not been finalized at this
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time.</div>
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</li>
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<li>System Look and Feel
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<div>Currently, we have two interfaces, nsILookAndFeel and nsIDeviceContext
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that can both be asked for information about CSS fonts, colors, etc. These
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have been merged in to a single <a href="http://www.pavlov.net/gfx2/class_nsISystemLook.html">nsISystemLook</a>
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interface that contains all of this information.</div>
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</li>
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</ul></div>
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</li>
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</ul>
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</div>
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<hr/>
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<h2>Documentation</h2>
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<div>
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<ul>
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<li>The GFX2 interfaces are full documented using doxygen and JavaDoc style comments.
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See <a href="http://www.pavlov.net/gfx2/annotated.html">the full list of
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interfaces and information</a>.
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</li>
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</ul>
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</div>
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<hr/>
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<h2>Questions</h2>
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<div>
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<ul>
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<li><h3>Is GFX2 thread safe?</h3>
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<div>The implementations are probably not, however an attempt has been made to make
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the interfaces reentrant (with noted exceptions such as nsIClipboard). </div>
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</li>
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<li><h3>Will GFX2 break existing platforms such as BeOS and OS/2?</h3>
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<div>No, an adaptation layer will be made that will convert calls made to the new GFX2
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APIs in to the old APIs allowing current implementations to continue working
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until they are ported.</div>
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</li>
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<li><h3>Should GFX2 interfaces use XPCOM?</h3>
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<div>
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<ul>
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<li>Pro
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<div><ul>
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<li>Scriptability
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<div>Having the interfaces be scriptable makes writing test cases for them much
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easier. To help people writing new implementations and porting to new platforms,
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having a test suite that tests all of their code will make a huge difference.
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We can also use scriptability to do things like check event ordering from
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windows, etc.</div>
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</li>
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<li>Run Time Switching
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<div>Having GFX2 use XPCOM interfaces allows us to change toolkits at runtime.
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This may not seem like a big win, but imagine us shipping an Xlib based browser
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for Unix systems and someone wants to run using NanoX. They could use our Unix
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builds and simply switch out their GFX2 implementation for their own without
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having to build the whole product specifically for them.</div>
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</li>
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</ul></div>
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</li>
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<li>Con
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<div><ul>
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<li>Speed
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<div>Due to the cost of virtual functions, it will be a bit slower than if we did
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not use XPCOM for GFX2. If the GFX2 library was linked to other libraries,
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the compiler/linker might be able to further optimize the code paths.</div>
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</li>
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</ul></div>
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</li>
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<li>Overall
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<div><ul>
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<li>Should We Use XPCOM?
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<div>After spending time looking at the usage patterns of GFX through layout, using
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XPCOM should provide only an insignificant speed hit, while providing us with
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scriptability and run time switching of implementations. Time would be better
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spent removing XPCOM interfaces by focusing on interfaces such as nsISupportsArray
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that are used constantly throughout the entire code base.</div>
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</li>
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</ul></div>
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</li>
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</ul>
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</div>
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</li>
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<li>Is GFX2 Y2K Compliant?
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<div>Maybe.</div>
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</li>
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</ul>
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</div>
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<hr/>
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<p>comments/questions: email <a href="mailto:pavlov@netscape.com">Stuart Parmenter</a></p>
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