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Comment by aroman | Hacker News Reader

Looks great. I was impressed that the keyboard visualization handled up to 7 simultaneous button pressed on my physical keyboard. Honestly, I wasn't aware my keyboard's wiring (MacBook Air) was capable of handling that.

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It doesn't have to do with hardware, it's just client-side implementation. I had to write code for multiple key presses before. The browser will normally trigger a keydown and keyup event whenever something is pressed and released. The trick is to keep an array of keyCodes representing current keydowns; during keydowns add to array and during keyups, remove from array.

It is hardware related. USB has a maximum rollover limitation of 6 keys + 4 modifiers. Though keyboards can have n-key rollovers (i.e., greater than 10 keys simultaneously), you have to use PS/2.

See https://en.wikipedia.org/wiki/Rollover_(key)

I don't know the details, but it is possible for a USB keyboard to support N-key rollovers. As an example: http://www.corsair.com/en/support/faq/vengeance-gaming/

Do they require custom drivers? I see no reason you can't have all-key rollover with that, unless the OS refuses to do so.

Not that I'm saying you're wrong, I really don't know if normal driverless keyboard input is capable of this. I certainly hope so. I just see essentially all 10-key rollover (or more) keyboards using PS/2 and citing that it doesn't work through USB.

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