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Old 01 March 2016, 19:52   #1
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Measuring/comparing display latency or reaction time

[This isn't specific to WinUAE since it could be useful on real hardware too.]

Has anyone written an Amiga program to compare video output latency? For example, the program could flash the screen white at semi-random intervals, and time how long the user takes to click the mouse button on seeing each flash.

The idea would be that, after averaging the results of several/many flashes, you could arrive at some measurement of display latency. Well, actually also the user's reaction time and input latency plus display latency.

For real hardware that could allow the user to get some idea of how the "game mode" or other settings of their LCD TV might affect latency. For WinUAE the user could experiment with different display options (buffering, D3D/DirectDraw). And maybe how different input devices could vary in latency (PS/2 keyboard vs USB?). Choosing the lowest-latency options could help in games like Pinball Dreams etc.

Perhaps there already exists some reaction-time-testing program or game???

Slightly related, a Google search brought up a 1986 article "Amiga 1000 hardware timing and reaction-time key interfacing" from the journal Behavior Research Methods. (PDF download link on that page.)

Edit 2: There's a reaction time tester program R²Z - Reiz-Reaktion-Zeit. Not sure how ideal that is, but it's a start. To minimise variation/latency, an ideal reaction time tester would probably kill the OS then poll for joystick/mouse button presses in a tight loop. Is polling joystick directions (via JOY0DAT/JOY1DAT) faster than fire buttons (via CIAAPRA)?

Last edited by mark_k; 01 March 2016 at 21:18.
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Old 02 March 2016, 15:39   #2
Toni Wilen
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Originally Posted by mark_k View Post
Is polling joystick directions (via JOY0DAT/JOY1DAT) faster than fire buttons (via CIAAPRA)?
If there is any difference (mouse/joystick data being multiplexed and also serial in AGA), it still will be less than single scanline. CIA access is practically instant.

Second/third firebutton is slower than first button due to POT capacitors, still only max 20-30us.
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Old 02 March 2016, 16:15   #3
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I think human response is much slower than the delay introduced from emulation or display lag. You would never be able to measure it very accurately like that.
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