NewModelViewArchitecture

Homepage for the WIP Model-View architecture for CEGUI widgets!

Introduction

The new architecture aims to unify the underlying implementation of several widgets so that they will use a common base model provider. This will involve a lot of ABI and API breakage.

Proposed architecture

TODO - decide on another concepts than row/column

ModelIndex

Identifies uniquely items in the model.

Properties:

• row : size_t
• column : size_t
• parent : ModelIndex
• modelData : void * (protected)

Methods:

• isValid

Since ModelIndex will be friend with the ViewModel, only the VM will be able to use the model data and thus prevent View(s) to use it by mistake.

ViewModel

The model for the view, that provides data like items count to the view. This is implemented by the developers that want to use this new architecture.

Structure-related methods:

• rowCount(modelIndex)
• columnCount(modelIndex)
• makeIndex(row, column, parentModelIndex)
• getParentIndex(modelIndex)

Data-provider methods:

• getString(modelIndex)
• getImage(modelIndex)

Events:

• Rows/ColumnsAdded - startIndex, count
• Rows/ColumnsRemoved - startIndex, count
• Rows/ColumnsDataChanged - startIndex, count

TODO: Should we instead allow for a rectangular notification area? Like: startIndex / endIndex ?

ModelIndex Invalidation

Views might (read: will) store indices for a faster rendering or operations on the view. But these indices might become invalid if:

• the underlying model instance changes (i.e.: model is set to another instance)
  • Solution: Just invalidate the memorized indices
• an index from the "middle" is removed
  • Solution1: Create persistent model indices, like Qt does.
    • Con: too much management required, prone to errors.
  • Solution2: Query the model for validity
    • isValid will be moved to the ViewModel
  • Solution3: Other?

Affected widgets

Changed (to the new architecture) widgets

• ComboBox + ComboDropList -> ComboView
• Tree -> TreeView
• ListBox -> ListView

New widgets

• GridView
• ListBoxWidget (combines model & view together for simple usage cases)

Removed/deprecated widgets

• MultiColumnList (replaced by GridView)
• ItemListbox (duplicated by ListBox)

To decide

• ItemListBase
  • It's used in other places like: MenuBase and ScrolledItemListBase
  • Remove the other usages as well?

Workflow examples

List rendering

• Create root model index (parent=0)
• Query the number of rows for root
• For each row (value=[0, rowCount))
  • Create row model index (row=current row value, parent=rootModelIndex)
  • Query the image to be displayed for row index
  • Draw image
  • Query the text to be displayed for row index
  • Draw text
• Render non-row elements