jorimt wrote: ↑
01 Jun 2020, 09:07
hmukos wrote: ↑
01 Jun 2020, 08:03
Wait, isn't your picture only about fixed scan rate case? Where would advantage in first reaction come in the XG248 case in Chief's picture below?
Because I'm pretty sure it would then look something like this:
Sync technology matters.
And lag measurement method matters (single point photodiode versus first-anywhere measurement)
Corresponding latency for a game stimuli, assuming full-screen reaction (So first-anywhere is identical).
For VSYNC OFF, won't be delayed. The new frame will tear earlier at 60Hz, but will tear briefer (1/4th the frameslice height at 240Hz).
Now imagine the frameslices are color coded. The color code location will determine the location of the lag. The image is simply vertically stretched in the diagram only to align the scanouy positions between 60Hz and 240Hz. Frameslices are 4x taller at 240Hz cable scanout than 60Hz cable scanout.
To make this easier to imagine, it'll be the exact same aligned frameslice. Instead of grey-darkgrey, imagine separate colors for each frameslice. The color will be the lag of that frameslice, relative to top edge.
So 4.2ms is only 1/4th down the 60Hz scanout.
So TL;DR for VSYNC OFF, for a T+3.5ms or T+4.0ms sample, as indicated in red;
from a screen vertical position perspective
(A) 60Hz visibility will be nearer top edge of screen, but a tiny frameslice
(B) 240Hz visibility will be nearer bottom edge of screen, but a 4x height frameslice
from a latency perspective:
60Hz and 240Hz frameslice absolute latency is the same (albiet different vertically-stretched latency gradients)
However, realworld latency to human vision and fullscreen cameras is lower because of the 4x-height frameslice, delivering more imagery per refresh cycle at 240Hz, despite same absolute latency. This creates lower "first onscreen reaction" latencies at 240Hz.
The problem is game reactions aren't always global fullscreen changes. Which creates an interation to the fact that not all pixels refresh at the same time as seen in those videos
. Since first-anywhere reactions are sometimes tiny objects, the fact that 60Hz frameslices will be 1/4th the height of 240Hz frameslices at the same framerate, will usually miss those reactions happening elsewhere. Therefore, statistically sampled over hundreds and thousands of samples (like G-SYNC 101), the "first-anywhere" reactions will always be lower for 240Hz, even if absolute latency is identical for 60Hz and 240Hz (for a pixel-for-pixel latency), even for scanrate-multisync panels too! The faster scanout spews more pixels per frameslice at higher Hz, helping to increase statistical likelihood that a game stimuli is displayed as photons sooner to human eyeballs.
To throw another complication into matters, frameslices are individual latency gradients, so 2000fps at consitent frametimes = a latency gradient of 1/2000sec from the top edge to bottom edge of frameslice.