Higher FPS with region render

[mattjgerard]

So, we render all of our images 2500x2500 for the website (Adobe AEM scales them to whatever is needed) Some of our products are long LED lighting tubes, and therefore only take up the center 10% of the image area when in the vertical orientation. In doing a lot of material development for some cloudy plastic materials with area lights behind, I'm using region render quite a bit to speed up the process. I noticed that even though 80-90% of the realtime preview window is just plain white, the FPS is hovering around 27-30. Now, if I draw a render region box around the light stick, the FPS runs up to 145!!

Now, I have no problem using render region while on my local machine, but when I send to the network render, is this huge difference still being put into place  because of the unused space around the object? There is no floor, no shadows, no reflections, rendering with an alpha all the time, so there is no background to render, no interaction with anything else in the scene. lighting is all HDRI , nothing crazy. Using new experimental product mode.

So, here are some test numbers-

Standard Product mode-
Full screen - 3fps
Render region - 35fps

Experimental Product Mode -
Full Screen - 28fps
Render Region - 145fps

[DMerz III]

From my understanding  region render is going to boost your FPS because there are less pixels that need to be calculated and displayed. Even if there is white space, those pixels still need to be calculated to determine, and then displayed. The calculating in the white space is of course fast, but still uses processing power.

A 3000 by 3000 pixel image means 9 million pixels need to be accounted for.

A region of that? Let's say 1000 x 1000 pixel area, well that drastically drops the # of pixels needed for calculation/displaying to just 1 million. That's 9 times less! For an area that seemingly is only 3 times smaller in width/height.