TeaCrab

No, I'm using Windows 7 on a desktop, always in high-performance mode. I think it's due to I used 2 graphic cards that shares different architecture.

Thanks for the advice Despite what GPU you might be using, there are too much reason for it to work or not work.. lol It's probably just magic and I don't think I want to spend hours to test it again...

Apprently, I had GTX 970 and GTX 660ti installed at the same time. And the software is using both. It gives me super faster render time for Ambient Occlusion maps, but I think it's causing all other issues. So I took out my 660ti. I've also reset my scene, so now the second object is using 1024 texture resolution, which greatly reduced the input lag to a tolerable level. And, the fact that 660ti + 970 together can give me a super faster Ambient Occlusion Texture bake is pretty interesting, I literally waits only 3 sec for a 256 lights, 1 smooth for two 2048x2048 textures, with 4.5 beta of course. Now with my single 970, AO bake time increased to like 10 sec or so for 128 lights and 1 smooth for one 2048 and one 1024 texture. Im going back to 4.5, even though it's not stable, some bits and pieces of the improvement just doesn't let me go back. And, no backward compatibility.

I don't know what is happening in 4.5 beta, but I got back to 4.1.17, and the issue is gone.

Update, So after more work & test, this is what I found: The bigger the triangle size is in relation to the entire UV, the more lag I got. Again, drawing inside texture editor has no lag at all, but symmetry doesn't work. Only when drawing in 3D viewport, the lag happens. As the screen shot above. You can see Purple and Red color I painted on 2 places on the model with different UV density. The Purple ones I drew, I experienced tremendous amount of lag. The Red ones I drew, I only experienced none, or little amount of lag. It's magical.

So I've got this input lag, it feels like cpu can't keep up or something. The situation: I imported 2 FBX file, with about 10 object, all very low poly. 2 UV sets using 2 materials. I was painting Color ID information. Every paint stroke on my initial object/first imported object are smooth and super responsive. When I switch to the second UV set/second imported object, when I paint, something goes nut and things become quite not responsive, and lags behind. It's not smoothing stroke [alt+s] issue. And whenever I go back to my first object, the lag just doesn't exist. Whenever I go to second object/second UV set, it just lags. I don't know how to create 2 sets of layers for each of the object, so I'm using same layers for both object, their UV will overlap if they existed in same UV space(Which I put them in 2 UV sets, so maybe it should be different UV space?). I'm using 4.5 beta.

Quoted myself for a mistake: H is completely IRRELEVANT.

I was using the [Rotate Around Current Pick Point] Option. btw, I'm talking about texture Editor, not 3D viewport.

I draw in texture editor for better color ID/ no bleeding on sharp edge geometry. I noticed that, when I place my Texture Editor UV vertically above my 3D Viewport, the zoom pivot point is located almost inside my viewport. Then I moved the texEditor to the side of my view port, it then pivots at almost middle of the screen. I tested a little bit more. I found out that the formula for the location of the pivot point: Define: of the texture editor's viewport W = Width H = Height (x, y) = coordinates of the Zoom Pivot Point of texture editor. Function: (x, y) = (W/2, W/2) So... H is completely relevant. This is magical... So... if you don't want annoy yourself to death, don't place texture editor above or below the 3D viewport; Unless you are using a vertical monitor or you shrink the texture editor into a really small square. There are not enough vertical space on wide screen monitors to make this work. So yea, keep your texture editor square shaped, or it will pivot at non-center. End of story. Awaiting OCD to cool down.