think-cell technical report TC2003/01 A GUI-based Interaction ...

5.1 Program Architecture IMPLEMENTATION
levels. The union set of all UI objects is then returned.
Figure 40 gives an idea of how user interaction propagates through the system
and finally generates appropriate on-screen feedback. When the framework inter-
cepts a mouse event message, such as ButtonDown, the message gets forwarded to
the responsible document window and its UI objects. Each UI object has to make
a decision if it is concerned by that mouse action, depending on the current mouse
pointer location and possibly other UI objects concurrently capturing the mouse.
If appropriate, the UI object puts its respective visual elements into another state
– say, highlight – to reflect its responsiveness. Moreover, the UI object that was hit
calls its own OnClick() method that finally applies the intended changes to the data
model. Meanwhile, the visual element has notified the framework of the invalidation
of the screen region where a change in the UI occurred.
Depending on the effect that the mouse interaction had on the underlying data
model, the smart grid, its shapes and its UI objects may explicitly be called to
update themselves. The propagation of UpdateShapes() and UpdateUI() messages
are not reflected in the sequence diagram; they take similar paths as the CreateUI()
message in figure 39. At some point in time, there will be a Paint() message
generated from the framework, which causes the visual elements to update their
texture mapping with regard to current document and screen coordinates, and
finally reflects the internal state on the screen.
User
Mouse event
visual feedback
... ButtonDown()
... Paint()
:CPPTDocWnd
ButtonDown()
Paint()
:CUIObject
Highlight()
Paint()
:CVisualElement
OnClick()
SetDirtyRect(...) ...
Modify()
BuildScreenPoints()
TextureMapping(...)
Figure 40: Processing of user input and generation of visual feedback
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:CFeature