About the Frame-Rate of Hardware-Accelerated Animations.

One of the subjects which I’ve posted about before, is that in the case of typical hardware-accelerated animations, the frame-rate, which some people just know as ‘the FPS of the animation’, is actually lower than the refresh-rate of the monitor.

Well, if the user is running Plasma 5 as his desktop-manager – which is Linux-based – then he can open ‘System Settings -> Desktop Behaviour -> Desktop Effects’, and he will see a list of available compositing effects, that would all be hardware-accelerated, and under the section of ‘Tools’, there is an effect named ‘Show FPS’. Enabling that effect, and then clicking on ‘Apply’, will cause a piece of OSD information to display, that actually shows the frame-rate. The user will notice that it does not equal the refresh rate of his monitor.

But there is a catch to this. Often, the rendering software will place an upper limit on the frame-rate. Frame-rates actually higher than the refresh rate of the display device accomplish no useful purpose, and there used to be a simple, command-line test which Linux users could run, which was called ‘glxgears’. This would display a very simple animation, of a red, a green and a blue gear, rotating smoothly. In very early versions of this test-program, a frame-rate of something unreasonable, such as 2000 or maybe even 5000 FPS might result, which simply represents a waste of GPU power. The gears would still rotate at the same, correct apparent speed, but each frame-cycle would be fewer than 1 millisecond apart on average. Therefore, more-recent versions of this test-program will cap the frame-rate at the refresh rate of the monitor, and the gears will display as rotating at the same, smooth speed.

Dirk

 

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