1686810 - The FPS display in the WR profiler overlay shows confusing values

Status: RESOLVED FIXED

(Core :: Graphics: WebRender, defect)

Description

[Markus Stange [:mstange]]

When you enable the WR profiler overlay with the gfx.webrender.debug.profiler pref, there's an FPS number displayed in the top left corner. That number updates twice a second.

The FPS number that is displayed is very confusing. It does not display how many frames we rendered within a second. Instead, it is based on the slowest time between two subsequent frames that was encountered in the current half-second window:

set_text!(&mut text_buffer, "{:.2} fps", 1000.0 / self.counters[FRAME_TIME].max);

So if you have a 60fps animation, but skip one frame, it'll display 30 fps because the skipped frame causes a single 33ms frame time. In this scenario, I would expect a number of 59fps instead.

In practice, the counter jumps around wildly and always looks worse that what the actual performance is.

Comment 1

[Markus Stange [:mstange]]

Attachment: Bug 1686810 - Make the fps counter display the number of frames rendered within the last second. r=nical

Comment 2

[Pulsebot]

Pushed by [e-mail]:
https://hg.mozilla.org/integration/autoland/rev/e9cd13398944
Make the fps counter display the number of frames rendered within the last second. r=nical

Comment 3

[Natalia Csoregi [:nataliaCs]]

https://hg.mozilla.org/mozilla-central/rev/e9cd13398944