I imagine this is more of a question for hardware folks, but it's something that has boggled me for many years now.
As we all know LCDs (think TFT LCDs, but IPS vs. TFT vs. PVA vs. MVA is not the topic) lack an electron gun, i.e. this nonsense should no longer apply to the same degree as in the past.
It's this fact that has always made me wonder how VBlank and HBlank actually work on an LCD. Tearing (example 2) does in fact happen on LCDs, even though (logically, in my mind) you would expect to see no such thing for a couple of reasons (mainly that there's no electron gun, and the fact that transistor updates on LCDs only happen when there's an actual change).
I'm focusing on LCDs hooked up via pure digital, by the way, such as DVI (not using the analog pins) or HDMI. In the case of DVI's analog pins, sure pins 8 and C4 are used for vertical and horizontal sync -- and the same Wikipedia article references that DVI's digital interface offers synchronisation capabilities, so there must be "something" going on between the LCD and the video adapter.
The only idea I can come up with is that HBlank and VBlank are effectively emulated using some sort of arbitrary delay/timing mechanism, e.g. HBlank would consist of a delay after the monitor updates all the transistor switches on pixel row X but before starting on pixel row X+1, e.g. VBlank would consist of a delay after the monitor updates the final/last row of transistors at the bottom but before returning to pixel row 0.
Thoughts/insights?
As we all know LCDs (think TFT LCDs, but IPS vs. TFT vs. PVA vs. MVA is not the topic) lack an electron gun, i.e. this nonsense should no longer apply to the same degree as in the past.
It's this fact that has always made me wonder how VBlank and HBlank actually work on an LCD. Tearing (example 2) does in fact happen on LCDs, even though (logically, in my mind) you would expect to see no such thing for a couple of reasons (mainly that there's no electron gun, and the fact that transistor updates on LCDs only happen when there's an actual change).
I'm focusing on LCDs hooked up via pure digital, by the way, such as DVI (not using the analog pins) or HDMI. In the case of DVI's analog pins, sure pins 8 and C4 are used for vertical and horizontal sync -- and the same Wikipedia article references that DVI's digital interface offers synchronisation capabilities, so there must be "something" going on between the LCD and the video adapter.
The only idea I can come up with is that HBlank and VBlank are effectively emulated using some sort of arbitrary delay/timing mechanism, e.g. HBlank would consist of a delay after the monitor updates all the transistor switches on pixel row X but before starting on pixel row X+1, e.g. VBlank would consist of a delay after the monitor updates the final/last row of transistors at the bottom but before returning to pixel row 0.
Thoughts/insights?