<html><head><title>[xgap] 6.1 Graphic Sheet Objects</title></head> <body text="#000000" bgcolor="#ffffff"> [<a href = "C006S000.htm">Up</a>] [<a href ="C006S002.htm">Next</a>] [<a href = "theindex.htm">Index</a>] <h1>6.1 Graphic Sheet Objects</h1><p> <p> To access any graphics in XGAP you first have to create a <strong>graphic</strong> <strong>sheet</strong> object. Such objects are linked internally to windows on the screen. You do <strong>not</strong> have to think about redrawing, resizing and other organizing stuff. The graphic sheet object is a <font face="Gill Sans,Helvetica,Arial">GAP</font> object in the category <code>IsGraphicSheet</code> and should be saved because it is needed later on for all graphic operations. <p> <a name = "SSEC1"></a> <li><code>GraphicSheet( </code><var>title</var><code>, </code><var>width</var><code>, </code><var>height</var><code> ) O</code> <p> creates a graphic sheet with title <var>title</var> and dimension <var>width</var> by <var>height</var>. A graphic sheet is the basic tool to draw something, it is like a piece of paper on which you can put your graphic objects, and to which you can attach your menus. The coordinate <var>(0,0)</var> is the upper left corner, <var>(<var>width</var>-1,<var>height</var>-1)</var> the lower right. <p> It is possible to change the default behaviour of a graphic sheet by installing methods (or sometimes called callbacks) for the following events. In order to avoid confusion with the <font face="Gill Sans,Helvetica,Arial">GAP</font> term ``method'' the term ``callback'' will be used in the following. For example, to install the function <code>MyLeftPBDownCallback</code> as callback for the left mouse button down event of a graphic sheet <var>sheet</var>, you have to call <code>InstallCallback</code> as follows. <p> <pre> gap> InstallCallback( sheet, "LeftPBDown", MyLeftPBDownCallback ); </pre> <p> XGAP stores for each graphic sheet a list of callback keys and a list of callback functions for each key. That means that when a certain callback key is triggered for a graphic sheet then the corresponding list of callback functions is called one function after the other. The following keys have predefined meanings which are explained below: <code>Close</code>, <code>LeftPBDown</code>, <code>RightPBDown</code>, <code>ShiftLeftPBDown</code>, <code>ShiftRightPBDown</code>, <code>CtrlLeftPBDown</code>, <code>CtrlRightPBDown</code>. All of these keys are strings. You can install your own callback functions for new keys, however they will not be triggered automatically. <p> <a name = "SSEC2"></a> <li><code>Close( </code><var>sheet</var><code> )</code> <p> the function will be called as soon as the user selects ``close graphic sheet'', the installed function gets the graphic sheet <var>sheet</var> to close as argument. <p> <a name = "SSEC3"></a> <li><code>LeftPBDown( </code><var>sheet</var><code>, </code><var>x</var><code>, </code><var>y</var><code> )</code> <p> the function will be called as soon as the user presses the left mouse button inside the graphic sheet, the installed function gets the graphic sheet <var>sheet</var>, the <var>x</var> coordinate and <var>y</var> coordinate of the pointer as arguments. <p> <a name = "SSEC4"></a> <li><code>RightPBDown( </code><var>sheet</var><code>, </code><var>x</var><code>, </code><var>y</var><code> )</code> <p> same as <code>LeftPBDown</code> except that the user has pressed the right mouse button. <p> <a name = "SSEC5"></a> <li><code>ShiftLeftPBDown( </code><var>sheet</var><code>, </code><var>x</var><code>, </code><var>y</var><code> )</code> <p> same as <code>LeftPBDown</code> except that the user has pressed the left mouse button together with the <var>SHIFT</var> key on the keyboard. <p> <a name = "SSEC6"></a> <li><code>ShiftRightPBDown( </code><var>sheet</var><code>, </code><var>x</var><code>, </code><var>y</var><code> )</code> <p> same as <code>LeftPBDown</code> except that the user has pressed the right mouse button together with the <var>SHIFT</var> key on the keyboard. <p> <a name = "SSEC7"></a> <li><code>CtrlLeftPBDown( </code><var>sheet</var><code>, </code><var>x</var><code>, </code><var>y</var><code> )</code> <p> same as <code>LeftPBDown</code> except that the user has pressed the left mouse button together with the <var>CTRL</var> key on the keyboard. <p> <a name = "SSEC8"></a> <li><code>CtrlRightPBDown( </code><var>sheet</var><code>, </code><var>x</var><code>, </code><var>y</var><code> )</code> <p> same as <code>LeftPBDown</code> except that the user has pressed the right mouse button together with the <var>CTRL</var> key on the keyboard. <p> Here is the documentation for the operations to control the callback functions: <p> <a name = "SSEC9"></a> <li><code>InstallCallback( </code><var>sheet</var><code>, </code><var>key</var><code>, </code><var>func</var><code> ) O</code> <p> Installs a new callback function for the sheet <var>sheet</var> for the key <var>key</var>. Note that the old functions for this key are <strong>not</strong> deleted. <p> <a name = "SSEC10"></a> <li><code>RemoveCallback( </code><var>sheet</var><code>, </code><var>func</var><code>, </code><var>call</var><code> ) O</code> <p> Removes an old callback. Note that you have to specify not only the <var>key</var> but also explicitly the <var>func</var> which should be removed from the list! <p> <a name = "SSEC11"></a> <li><code>Callback( </code><var>sheet</var><code>, </code><var>key</var><code>, </code><var>args</var><code> ) O</code> <p> Executes all callback functions of the sheet <var>sheet</var> that are stored under the key <var>func</var> with the argument list <var>args</var>. <p> Every graphic object in XGAP can be <var>alive</var> or not. This is controlled by the filter <code>IsAlive</code>. Being <var>alive</var> means that the object can be used for further operations. If for example the user closes a window by a mouse operation the corresponding graphic sheet object is no longer <var>alive</var>. <p> <a name = "SSEC12"></a> <li><code>IsAlive( </code><var>gobj</var><code> ) F</code> <p> This filter controls if a graphic object is <var>alive</var>, meaning that it can be used for further graphic operations. <p> The following operations apply to graphic sheets: <p> <a name = "SSEC13"></a> <li><code>Close( </code><var>sheet</var><code> ) O</code> <p> The graphic sheet <var>sheet</var> is closed which means that the corresponding window is closed and the sheet becomes <var>not alive</var>. <p> <a name = "SSEC14"></a> <li><code>Resize( </code><var>sheet</var><code>, </code><var>width</var><code>, </code><var>height</var><code> ) O</code> <p> The <var>width</var> and <var>height</var> of the sheet <var>sheet</var> are changed. That does <strong>not</strong> automatically mean that the window size is changed. It may also happen that only the scrollbars are changed. <p> <a name = "SSEC15"></a> <li><code>WindowId( </code><var>sheet</var><code> ) A</code> <p> Every graphic sheet has a unique number, its <var>window id</var>. This is mainly used internally. <p> <a name = "SSEC16"></a> <li><code>SetTitle( </code><var>sheet</var><code>, </code><var>title</var><code> ) O</code> <p> Every graphic sheet has a title which appears somewhere on the window. It is initially set via the call to the constructor <code>GraphicSheet</code> and can be changed later with this operation. <p> <a name = "SSEC17"></a> <li><code>SaveAsPS( </code><var>sheet</var><code>, </code><var>filename</var><code> ) O</code> <p> Saves the graphics in the sheet <var>sheet</var> as postscript into the file <var>filename</var>, which is overwritten, if it exists. <p> <a name = "SSEC18"></a> <li><code>FastUpdate( </code><var>sheet</var><code>, </code><var>flag</var><code> ) O</code> <p> Switches the <code>UseFastUpdate</code> filter for the sheet <var>sheet</var> to the boolean value of <var>flag</var>. If this filter is set for a sheet, the screen is no longer updated completely if a graphic object is moved or deleted. You should call <code>FastUpdate( </code><var>sheet</var><code>, true )</code> before you start large rearrangements of the graphic objects and <code>FastUpdate( </code><var>sheet</var><code>, false )</code> at the end. <p> <p> [<a href = "C006S000.htm">Up</a>] [<a href ="C006S002.htm">Next</a>] [<a href = "theindex.htm">Index</a>] <P> <address>xgap manual<br>Mai 2003 </address></body></html>
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