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:

• do not share the layout-hints among GUI components;
• do not delete child widgets in the destructor as this is done automatically.

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:

TGVerticalFrame* TGedFrame::CreateEditorTabSubFrame(const Text_t *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:

void TGedEditor::ExcludeClassEditor(TClass* class, Bool_t recurse)

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.

Classes
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...