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7.2 Performance objectives

One of the biggest issues you will face when developing 3D applications is performance, which usually translates to rendering time. Rendering time defines how long the Java 3D renderer will take to render a single frame that is a view of your 3D scene. This, in turn, defines the FPS that will be achievable for your application. For games applications and smooth animation, a rate of 20 or more FPS is desirable. Obviously, the FPS that your application will achieve is inherently linked to the hardware that it is running on. When designing your application it is therefore vital to specify your performance objectives on specific platforms.

For example, you might want the application to achieve 30 FPS on a 500 MHz PC running Windows 98 with an nVidia GeForce MX video card. This typical system configuration (or target machine) must be the yardstick by which you judge your application and all the decisions you make while designing your application should be evaluated in the context of their impact on the performance of the application running on your target machine (or machines). During the initial design phase, you should run simulated tests on your target machine to evaluate your design decisions and assess whether the performance objectives are achievable.


A trap that developers sometimes fall into is to introduce features that look great on their development machines (which are typically high−end) but cause an overall degradation in performance on users’ machines (which are typically closer to the performance of the target machine).


Almost all 3D applications are interactive, that is, the user is able to influence the current point of view or camera and hence the rendered view. The required frame rate is often related to the mode of user interaction:

for 3D CAD visualization input is largely mouse or tablet driven and motion is usually confined to a small number of objects and is not continuous. Lower rates of five or more FPS may be acceptable. For interactive 3D games a frame rate is required that allows users to suspend belief and accept that they are moving within the scene. Lower frame rates provide a choppier motion and quickly destroy the impression of smooth movement, 20 or more FPS is typically required.


 

7.2.1 Rendering quality
7.2.2 Load time
7.2.3 Memory footprint
7.2.4 Development time and asset management