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[gui] rectangles and the CSS box model
by Reece Dunn 22 Dec '04

22 Dec '04

Hi All, In the "thoughts on a GUI component library" thread there have been various discussions about the layout of a rectangle and come relating to CSS. Note that point and size are stable. The CSS3 Values and Units module (http://www.w3.org/TR/2001/WD-css3-values-20010713/) defines various units (e.g. inches, picas and em). This is a good basis for a GUI library metric type. The type should store the values as a floating point to allow things like 2.71cm and also to support platforms that store coordinates as floating points (e.g. Cocoa). The CSS3 relative values (em and ex) are dependant on the inherited font-size property, so it is difficult to use these units as there is no associated font-size property. Another issue relating to this is how to resolve metric values between units that are not directly convertable. I have suggested using a device::resolve method that takes metric, point, size and rect types, but it may not always be possible to get access to a device. A further complication is the location of the origin. If we treat the origin as being in the top left corner (which is true for Windows, HTML/CSS and other document models such as text editors) this will simplify the design and for platforms that have a different model (e.g. Mac) then the implementation on that platform will need to map between the different representations. I personally like the CSS box model (http://www.w3.org/TR/css3-box/) which can be defined as: struct css::box_model { rect margin; rect border; rect padding; size dimensions; // width and height // T content; }; The problem with supporting it by default is that we would need: class component: public css::box_model; class graphics::object: public css::box_model; This clearly violates the don't pay for what you don't need rule of C++, so for a css_block_layout, it needs to contain the box model properties and a pointer to the component/graphical object. Obviously some level of support for the CSS box model should be provided, allowing an implementation of it to be written. There has been some discussion and disagreement as to what representation a rectangle takes. It is a good idea to hide the representation of a rectangle and provide accessors to the various values. This is because different people will want different things from it. However, for efficiency, it is a good idea to expose the members of point and size. In supporting the CSS box model and adoption of top-left as (0, 0) the representation becomes: class rect { point tl; point br; }; with: top() = tl.y; left() = tl.x; bottom() = br.y; right() = br.x; width() = br.x - tl.x; width( w ): br.x = tl.x + w; size() = ::size( width(), height()) center() = tl + ( size() / 2 ) An issue with this is: do we keep the width of the rectangle when setting left/right? In order to keep things simple, the answer has to be no. Construction of a rect should have the following variants: rect() = rect( 0, 0, 0, 0 ) rect( n ) = rect( n, n, n, n ) // This models the CSS "margin: 2px;" behaviour. rect( t, r, b, l ): tl( t, l ), br( b, r ) // This models "margin: 1pt 2pt 3pt 4pt;" rect( point p, size s ) = rect( p.x, p.y, p.x + s.dx, p.y + s.dy ) // This allows for support for traditional GUI representations Note that this model will change the nature of a program that uses the current model. We also have inflate/deflate operations that should take size *and* rect variants. This will allow easier box-model calculations: rect disp( point( 0, 0 ), size( 500, 700 )); rect margin( 1, 2, 3, 4 ); rect box = disp; box.deflate( margin ); // apply margin adjustments // ... Regards, Reece

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Re: [boost] mailing lists archives stuck
by JOAQUIN LOPEZ MU?Z 22 Dec '04

22 Dec '04

----- Mensaje original ----- De: Douglas Gregor <dgregor(a)cs.indiana.edu> Fecha: Miércoles, Diciembre 22, 2004 9:02 pm Asunto: Re: [boost] mailing lists archives stuck > On Dec 22, 2004, at 7:22 AM, Joaquín Mª López Muñoz wrote: > > To whom it may concern, the archives of the mailing lists, > > (for instance, http://lists.boost.org/MailArchives/boost/bydate.php) > > have stopped collecting messages since almost a week. > > The archives should be working again now. Thanks for the report! > Thanks for fixing the thing :) BTW, the *users* mailing list is also stuck :( As for the announce list, ist' hard to know, because its volume is so low. Joaquín M López Muñoz Telefónica, Investigación y Desarrollo

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mailing lists archives stuck
by Joaquín Mª López Muñoz 22 Dec '04

22 Dec '04

To whom it may concern, the archives of the mailing lists, (for instance, http://lists.boost.org/MailArchives/boost/bydate.php) have stopped collecting messages since almost a week. Joaquín M López Muñoz Telefónica, Investigación y Desarrollo

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Add conversion op doc to scoped_ptr
by cliffg＠codewrangler.net 22 Dec '04

22 Dec '04

This may already be known / in the queue / in CVS, but in case not ... The scoped_ptr synopsis and members does not document the unspecified-bool-type conversion operator that scoped_ptr provides (I didn't check scoped_array to see if the same issue is present or not.) I found this when a couple members of my team converted code from shared_ptr to scoped_ptr, with the original code relying on the conversion operator, and I was surprised when everything compiled cleanly (without adding the appropriate get() calls). Cliff

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Help \ Advice requested on getting the return type from a Lambda fctor
by Brian Braatz 22 Dec '04

22 Dec '04

I wrote up the simple example that shows what I am trying to figure out Basically, I am trying to pull the deduced return type (or explicitly passed as a template param in lambda bind()) in my template. If I have a function that is receiving a functor, I would like to be able to take that functor and pull the RETURN TYPE out of it. Lets say I have a function that returns a string: std::string ReturnAString() { return "this is a string"; } And then here is my template function (code below does not compile) template < typename TFUNCTOR> TFUNCTOR::result_type CallFctorDeduceRet( TFUNCTOR & functor) { return functor(); } Now here is my bind call std::cout << ( bind<std::string>(&ReturnAString)); Is there a way to GET to the return type in the Lambda fctor that was generated with a BIND call? I would like to be able to pull the <std::string> from the bind call and use it in the template function. It is not a problem for my template function to be dependant upon lambda bind. I have been going through the lambda code. And while it is brilliant, I am having a bit of difficulty figuring out what I am looking at (grin). Any help or direction is greatly appreciated FULL SAMPLE CODE HERE: template <typename CURRIEDTYPE> // Id class for currying type without creating the object class Id { public: typedef CURRIEDTYPE TYPE; }; // Explictly pass IN a return type template < typename TFUNCTOR, typename TRET> TRET CallFctorPassInRet ( TFUNCTOR & functor, Id<TRET> & ) { Id<TRET>::TYPE TRet; TRet = functor(); return TRet; } std::string ReturnAString() { return "this is a string"; } // try to get return type from the lambda fctor // Below does not compile- but it is along the lines of what I // WANT to do- note that I am trying to get from the Lambda functor the deduced return type template < typename TFUNCTOR> TFUNCTOR::result_type CallFctorDeduceRet( TFUNCTOR & functor) { return functor(); } void Test_LambdaRetDeduction() { std::cout << "CallFctorPassInRet returns [" << CallFctorPassInRet( bind(&ReturnAString), Id<std::string>()) << "]" << std::endl; // below is what I want to make work std::cout << "CallFctorDeduceRet returns [" << CallFctorDeduceRet( bind<std::string>(&ReturnAString)) << "]" << std::endl; }

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boost.sourceforge.net hacked?
by Joaquín Mª López Muñoz 22 Dec '04

22 Dec '04

Please take a look at http://boost.sourceforge.net/regression-logs/ ??? Joaquín M López Muñoz Telefónica, Investigación y Desarrollo

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RE: [boost] Unzipping the Boost distro
by Stefan Seefeld 22 Dec '04

22 Dec '04

> From: Richard Peters [mailto:r.a.peters@student.tue.nl] > If some boost authority certifies the released packages, and > users correctly > verify that the certificate is issued by the boost authority, and the > certificate is valid on the package, then certified executables can be > trusted as well. You are right, providing certificates is one thing. Whether or not to distribute executable self-extracting packages is different question. Regards, Stefan

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RE: [boost] Unzipping the Boost distro
by Stefan Seefeld 22 Dec '04

22 Dec '04

> From: Richard Peters [mailto:r.a.peters@student.tue.nl] > Another argument that I thought of this morning: suppose we > do not publish a > self-extracting executable. What is going to stop an attacker from not > uploading his own self-extracting look-alike? If he can > change existing > archives, he probably can add other archives as well. right, but if some boost authority certifies its released packages, everybody is free to ignore such look-alikes. Isn't that the whole point of certification ? Regards, Stefan

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automatic garbage collecting algorithm and its implementation in c++
by yilin yang 22 Dec '04

22 Dec '04

hi, everybody i've just designed and coded a garbage collecting infrastructure named u_canforget. it was uploaded onto the news group at boost.yahoo. the main idea is that we count the reference to track the life-cycle of the given object. as the new operator was overloaded to statisfy this requirement. the other important concept was the reference object. with the syntax represented by the redefined macros, the codes may be written in a very simple way with relationships automatically constructed, objects are freed without delete operater can be realized as well. i would keep tracking this thread, if there are any thought about this algorithm. thx for your advices. your's yilin. --------------------------------- Do You Yahoo!? 注册世界一流品质的雅虎免费电邮

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[gui] Representation of graphical objects
by Reece Dunn 22 Dec '04

22 Dec '04

Hi All, A GUI library can be thought of as having two distinct, but related, units: components (GUI widgets) and graphical objects/operations. A GUI component consists of data and events (e.g. a push button has a title and an onpressed() event). The question is: how do we represent the graphics unit? There are clearly two views: high level and low level. You can represent a graphics library as a series of objects (lines, circles, polygons, images, text, etc.) each of which having a set of properties (color, background/fill color, etc.). This is a high-level view and is based on the vector graphics model. Consider you are writing an application that draws a fractal object on the screen such as a Hilbert curve. You decide to represent it as a list of line objects. What happens when you redraw the curve? For large numbers of lines (easy when you have a fractal depth of 5+), the redrawing process is going to be slowed down. This is because you will be changing the colour on each line drawing operation. This becomes more apparent if you are using images to fill polygons and are using the same fill pattern across several objects. There are various graphics primitives (font, pen, fill (i.e. brush), etc.). Each primitive operates on a canvas and some can be used to query information on a device (e.g. the area occupied by a text string). In Windows a device and canvas are represented the same (as a HDC), but it makes sense to distinguish between them: you draw to a canvas and query information about a device. These graphical primitives should form the core of the graphics unit, with the high-level graphical objects being viewed as an extended unit. With the discussion on using CSS and Andy Little's comment about what difference is there between GUI components and graphical objects in terms of them both being objects that have position information and are drawn onto a canvas, it makes sense to allow both types to share a common interface. The main question is really what happens on the redraw phase? Ideally, components should not be drawn on the ondraw event, but rather be controlled by the behaviour of the operating system. For owner drawn components, do we handle the drawing event here or on the request of the OS (I think the latter is best). What about lightweight components (i.e. components that do not take up OS resources w.r.t. component representation, but that do support an event model)? Should we treat lightweight controls as graphical objects with an event model? Do graphical objects support an event model? Should graphical objects be treated as lightweight components? Regards, Reece

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