<![CDATA[Why graph draw FPS changing when resolution changed?]]>I draw graph and I use QWT Lib. Also I use OpenGL canvas for QWT plot.

For example :
When I use 1920x1080 window size, FPS is 100,
and when I use 4K window size, FPS is 15.
(FPS values just for example, is slowing)

Why that happend ?

]]>https://forum.qt.io/topic/164780/why-graph-draw-fps-changing-when-resolution-changedRSS for NodeFri, 19 Jun 2026 15:31:45 GMTThu, 11 Jun 2026 12:27:14 GMT60<![CDATA[Reply to Why graph draw FPS changing when resolution changed? on Mon, 15 Jun 2026 07:06:35 GMT]]>There might be more performant versions of this (in general OpenGL can render to an offscreen target), but the easiest in the context of Qt would be to use a QPixmap as a QPaintDevice instead of a QWidget. The QPixmap can then displayed in its own widget as an image.

]]>https://forum.qt.io/post/838749https://forum.qt.io/post/838749Mon, 15 Jun 2026 07:06:35 GMT<![CDATA[Reply to Why graph draw FPS changing when resolution changed? on Fri, 12 Jun 2026 08:51:23 GMT]]>@SimonSchroeder said in Why graph draw FPS changing when resolution changed?:

You could try to render offscreen to an image of 1920x1080 and then display that image on a 4k display.

I don't know how to do this.

After reviewing the code a bit, I identified the root cause of the problem.
My issue is related to the waterfall plot (QwtPlotSpectrogram). This waterfall plot is constantly giving me trouble.

]]>https://forum.qt.io/post/838704https://forum.qt.io/post/838704Fri, 12 Jun 2026 08:51:23 GMT<![CDATA[Reply to Why graph draw FPS changing when resolution changed? on Fri, 12 Jun 2026 06:26:10 GMT]]>@Joe-von-Habsburg said in Why graph draw FPS changing when resolution changed?:

Is there a way to keep the resolution at fullhd even when using a 4K display?

You could try to render offscreen to an image of 1920x1080 and then display that image on a 4k display.

]]>https://forum.qt.io/post/838701https://forum.qt.io/post/838701Fri, 12 Jun 2026 06:26:10 GMT<![CDATA[Reply to Why graph draw FPS changing when resolution changed? on Fri, 12 Jun 2026 06:16:19 GMT]]>@JonB said in Why graph draw FPS changing when resolution changed?:

Every graphics game I play has lower FPS as you increase the resolution....

I know...

I have a question.
Is there a way to keep the resolution at fullhd even when using a 4K display?

]]>https://forum.qt.io/post/838700https://forum.qt.io/post/838700Fri, 12 Jun 2026 06:16:19 GMT<![CDATA[Reply to Why graph draw FPS changing when resolution changed? on Thu, 11 Jun 2026 12:52:08 GMT]]>@Joe-von-Habsburg
I know nothing about OpenGL or QWT. But since 4k resolution is many more pixels than 1920x1080 would you not expect/be unsurprised if the FPS drops? Every graphics game I play has lower FPS as you increase the resolution.... You either reduce the resolution, typically to your 1080p, or buy a better graphics card....

]]>https://forum.qt.io/post/838681https://forum.qt.io/post/838681Thu, 11 Jun 2026 12:52:08 GMT