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 *
• indexModelData : void *

Methods:

• isValid

ItemModel

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

Tree rendering

Full/first-time rendering

Triggered first time, or when whole model changes.

Recursive rendering procedure starting with a model index

• > Given a parent model index
• Query the number of rows for index
• For each row (value=[0, rowCount))
  • Create row model index (row=current row value, parent=parent<odelIndex)
  • Query the image to be displayed for row index
  • Draw image
  • Query the text to be displayed for row index
  • Draw text
  • Call procedure with row model index.

Actual rendering:

• Call procedure defined above with root model index (parent = 0)
• Render non-row elements

Item(s) modified/isolated rendering

Triggered when some parts of the model changed, but not all.