KoFormulaShape

KoFormulaShape is a flake shape ( derived from KoShape ) that implements the functionality to edit and show a mathematical formula. Its structure is highly related to the MathML markup language which is the ODF standard format for formula markup. At the moment the KoFormulaShape implements only parts of the MathML presentation markup, content markup is not supported.

Every formula is stored as a tree of element objects that more or less are equivalent to the XML structure of the MathML they were loaded from. The element objects are classes that derive all from the BasicElement class. They all implement a special interface which is used to alter and navigate through them.

The element tree's highest element is an object of the class FormulaElement. This object is a private member of the FormulaShape class which implements the public interface of a flake shape. The according flake tool is implemented in FormulaTool and contains an instance of FormulaEditor which is used for navigating and modifying the formula. A FormulaEditor holds a FormulaCursor that represents a position or selection in the formula, it consists of a start position, simply called position and (if selecting) an end position of the selection, called mark. It can be modified in various ways. The FormulaEditor provides methods for modifying the formula according to current cursor. These methods return a QUndoCommand, that is wrapped in a FormulaUpdateCommand (this has to be done to allow the notification of the shape/tool of data changes while keeping a separation between the kformulalib part and the flake part) and than pushed on the documents undo stack.

The complex system of attributes which can be hold by the single elements is completely implemented in the AttributeManager class. The attributes are generically loaded and stored inside the elements and obtain and parse their values the elements use AttributeManager which also deals with heritage and default values.

MathML specifies a scaling mechanism that uses the scriptlevel attribute. This mechanism is implemented in BasicElement using the m_scalingFactor. This is the factor the element is scaled in relation to its parent element. The value is determined in during layouting in FormulaRenderer class.

There are a number of elements that do not inherit BasicElement directly but instead through RowElement. These classes are referred to as the inferred row elements - see MathML spec 3.1.3.1.

Most other elements, especially those with a fixed number of childs, but also multiscript elements, inherit from FixedElement, which provides some convenience methods and default implementations to them.

The MathML specification lists default values for operator's layouting. These values are different for every element class so each of them implements a defaultAttributeValue() method that returns the hardcoded default value of the passed attribute.

The FormulaCursor class contains a current element, where the cursor is in. Each element provides a certain number of cursor positions, for example a token element has a cursor position before each letter and one at the end. The position and mark (as mentioned above) are in respect to the cursor positions of the current element. Each element implements a moveCursor method that is called with the cursor position before the move (oldCursor) and the (maybe already modified) new cursor position that the element changes according to it's direction. Additionally each element implements a acceptCursor method, where it can specify if it accepts this cursor (also according to it's position and selection state) or if the cursor should be moved further.