render model view special cases code delegation draw time
Pass-off special render cases to Model code.
Generic View code often becomes clotted with special cases, especially near the end of a project. Render Delegation gets the special cases out of the View code and into Model subclasses.
An example clot in View code:if (typeToDraw==DARTH_VADERS_SHIP) drawSpecialShieldEffect();To encapsulate these kinds of special cases, the View delegates the draw back to the Model. For example: objectToDraw->draw(x,y)
It is common for the view to do the transformation and sorting work and pass screen coordinates to the draw method of a model.
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Issues and Risks
Use Render Delegation when:
Don't use Render Delegation when:
- You want to ensure reusability / encapsulation of the renderer.
- The View code becomes clotted with special cases.
- Every model tends to have a different implementations of render.
- There are only a few special cases and the cost (compile time, encapsulation) of including render interfaces in Model code is very high.
Render Delegation passes draw commands from View to Model.
Render Delegation may be part of an Appearance Map.