Render Delegation
Submitted by Zachary Booth Simpson
on 12/5/2000

2000 - Zachary Booth Simpson. Copied with permission from http://www.mine-control.com/zack. If you find any of this work useful, please sign Zack's guest book: http://www.mine-control.com/cgi/gbook-zbs.cgi.

Intent

Pass-off special render cases to Model code.

Problem

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.

Solution

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.

Structure

Not available at this time.

Examples

No examples at this time. Email kevin@gamedev.net to contribute.

Issues and Risks

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.
  • Don't use Render Delegation when:

  • There are only a few special cases and the cost (compile time, encapsulation) of including render interfaces in Model code is very high.
  • Related Patterns

    Render Delegation passes draw commands from View to Model.

    Render Delegation may be part of an Appearance Map.

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    Date this article was posted to GameDev.net: 6/19/2001
    (Note that this date does not necessarily correspond to the date the article was written)

    See Also:
    Design Patterns

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