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ROOT Graphics Editor

Classes forming the Graphics Editor (GED) of ROOT and the basic classes of so-called object editors.

The ROOT Graphics Editor (GED)

Everything drawn in a ROOT canvas is an object. There are classes for all objects, and they fall into hierarchies. In addition, the ROOT has fully cross-platform GUI classes and provides all standard components for an application environment with common ‘look and feel'. The object-oriented, event-driven programming model supports the modern signals/slots communication mechanism. It handles user interface actions and allows total independence of interacting objects and classes. This mechanism uses the ROOT dictionary information and the Cling the C++ Interpreter to connect signals to slots methods.

Therefore, all necessary elements for an object-oriented editor design are in place. The editor complexity can be reduced by splitting it into discrete units of so-called *object* *editors*. Any object editor provides an object specific GUI. The main purpose of the ROOT graphics editor is the organization of the object editors' appearance and the task sequence between them.

Object Editors

Every object editor follows a simple naming convention: to have as a name the object class name concatenated with ‘*Editor*' (e.g. for **TGraph** objects the object editor is **TGraphEditor**). Thanks to the signals/slots communication mechanism and to the method DistanceToPrimitive() that computes a ‘‘distance'' to an object from the mouse position, it was possible to implement a signal method of the canvas that says which is the selected object and to which pad it belongs. Having this information the graphics editor loads the corresponding object editor and the user interface is ready for use. This way after a click on ‘axis'—the axis editor is active; a click on a ‘pad' activates the pad editor, etc.

The algorithm in use is simple and is based on the object-oriented relationship and communication. When the user activates the editor, according to the selected object **<obj>** in the canvas it looks for a class name **<obj>Editor**. For that reason, the correct naming is very important. If a class with this name is found, the editor verifies that this class derives from the base editor class **TGedFrame**. If all checks are satisfied, the editor makes an instance of the object editor. Then, it scans all object base classes searching the corresponding object editors. When it finds one, it makes an instance of the base class editor too.

Once the object editor is in place, it sets the user interface elements according to the object's status. After that, it is ready to interact with the object following the user actions.

The graphics editor gives an intuitive way to edit objects in a canvas with immediate feedback. Complexity of some object editors is reduced by hiding GUI elements and revealing them only on users' requests.

An object in the canvas is selected by clicking on it with the left mouse button. Its name is displayed on the top of the editor frame in red color. If the editor frame needs more space than the canvas window, a vertical scroll bar appears for easy navigation.

Histogram, pad and axis editors

Editor Design Elements

The next rules describe the path to follow when creating your own object editor that will be recognized and loaded by the graphics editor in ROOT, i.e. it will be included as a part of it.

(a) Derive the code of your object editor from the base editor class **TGedFrame**.

(b) Keep the correct naming convention: the name of the object editor should be the object class name concatenated with the word ‘‘Editor’`.

(c) Provide a default constructor.

(d) Use the signals/slots communication mechanism for event processing.

(e) Implement the virtual method SetModel(TObject *obj) where all widgets are set with the current object's attributes. This method is called when the editor receives a signal from the canvas saying that an object is the selected.

(f) Implement all necessary slots and connect them to appropriate signals that GUI widgets send out. The GUI classes in ROOT are developed to emit signals whenever they change a state that others might be interested. As we noted already, the signals/slots communication mechanism allows total independence of the interacting classes.

Creation and Destruction

GED-frames are constructed during traversal of class hierarchy of the selected object, executed from method **TGedEditor::SetModel()**. When a new object of a different class is selected, the unneeded GED-frames are cached in memory for potential reuse. The frames are deleted automatically when the editor is closed.

Note: A deep cleanup is assumed for all frames put into the editor. This implies:

Using Several Tabs

Sometimes you might need to use several tabs to organize properly your class-editor. Each editor tab is a resource shared among all the class-editors. Tabs must be created from the constructor of your editor-class by using the method:

char Text_t
Definition RtypesCore.h:62
char name[80]
Definition TGX11.cxx:110
A composite frame that layout their children in vertical way.
Definition TGFrame.h:374
virtual TGVerticalFrame * CreateEditorTabSubFrame(const char *name)
Create a vertical frame to be used by 'owner' in extra tab 'name'.

It returns a pointer to a new tab container frame ready for use in your class. If you need to hide/show this frame depending on the object's status, you should store it in a data member. See for examples: **TH1Editor**, **TH2Editor**.

Base-Class Editors Control

Full control over base-class editors can be achieved by re-implementing virtual method void TGedFrame::ActivateBaseClassEditors(TClass *cl). It is called during each compound editor rebuild and the default implementation simply offers all base-classes to the publishing mechanism.

To prevent inclusion of a base-class into the compound editor, call:

bool Bool_t
Definition RtypesCore.h:63
TClass instances represent classes, structs and namespaces in the ROOT type system.
Definition TClass.h:81
void ExcludeClassEditor(TClass *cl, Bool_t recurse=kFALSE)
Exclude editor for class cl from current construction.

Pointer to the compound GED-editor is available in **TGedFrame**‘s data-member:

TGedEditor *fGedEditor

Ordering of base-class editor frames follows the order of the classes in the class hierarchy. This order can be changed by modifying the value of **TGedFrame**'s data member Int_t fPriority. The default value is 50; smaller values move the frame towards to the top. This priority should be set in the editor constructor.


class  TArrowEditor
 Implements user interface for editing of arrow attributes: shape, size, angle. More...
class  TAttFillEditor
 Implements GUI for editing fill attributes. More...
class  TAttLineEditor
 Implements GUI for editing line attributes. More...
class  TAttMarkerEditor
 Implements GUI for editing marker attributes. More...
class  TAttTextEditor
 Implements GUI for editing text attributes. More...
class  TAxisEditor
 Implements GUI for axis attributes. More...
class  TCurlyArcEditor
 Implements GUI for editing CurlyArc attributes: radius, phi1, phi2. More...
class  TCurlyLineEditor
 Implements GUI for editing CurlyLine attributes: shape, size, angle. More...
class  TF1Editor
 GUI for TF1 attributes and parameters. More...
class  TFrameEditor
 Editor of frame objects. More...
class  TFunctionParametersDialog
 This class is used for function parameter settings. More...
class  TGedFrame
 Base frame for implementing GUI - a service class. More...
class  TGedMarkerPopup
 The TGedMarkerPopup is a popup containing buttons to select marker style. More...
class  TGedMarkerSelect
 The TGedMarkerSelect widget is a button showing selected marker and a little down arrow. More...
class  TGedPatternFrame
 The TGedPatternFrame is a small frame with border showing a specific pattern (fill style. More...
class  TGedPatternPopup
 The TGedPatternPopup is a popup containing a TGedPatternSelector. More...
class  TGedPatternSelect
 is a button with pattern area with a little down arrow. More...
class  TGedPatternSelector
 The TGedPatternSelector is a composite frame with TGedPatternFrames of all diferent styles. More...
class  TGedPopup
 is a popup window. More...
class  TGedSelect
 is button that shows popup window when clicked. More...
class  TGraphEditor
 Implements GUI for graph attributes. More...
class  TH1Editor
 Editor for changing TH1 histogram attributes, rebinning & fitting. More...
class  TH2Editor
 Editor for changing TH2 histogram attributes, rebinning & fitting. More...
class  TLineEditor
 Implements GUI for editing line attributes: shape, size, angle. More...
class  TPadEditor
 Editor of pad/canvas objects. More...
class  TPaveStatsEditor
 Implements GUI for editing attributes of TPaveStats objects. More...
class  TPieEditor
 Implements GUI for pie-chart attributes. More...
class  TPieSliceEditor
 Editor for changing pie-chart's slice attributes. More...
class  TStyleDialog
 This small class is useful to ask the user for a name and a title, in order to rename a style, create a new style or import a style from a canvas. More...
class  TStyleManager
 This class provides a Graphical User Interface to manage styles in ROOT. More...
class  TStylePreview
 This class may be used to preview the result of applying a style to a canvas. More...
class  TTextEditor
 Editor for changing TText's and TLatex's attributes. More...