This may be hard to test if your system is actually decent.
For whatever reason, if your computer can't quite keep up with a shader, Minecraft will decide to ignore your input instead of slowing down rendering. Now, if you have a decent graphics card, these steps won't work for you, but they work for my setup (listed in "Environment").
Steps to Reproduce:
1. Open the menu, and press "Super Secret Settings".
2. Observe that the 'fxaa' shader becomes active. For me, this does not cause any severe lag or issues. I can play the game just fine with this.
3. Click "Super Secret Settings" again.
4. Observe that the 'art' shader becomes active.
5. If your computer is anything like mine, it will continue rendering the world in the background (including animated things such as enchantment glows), and GUI buttons will still get highlighted when you hover over them. There may be an FPS drop, but not a complete lock-up.
6. Attempt to click any buttons, or Escape to exit the GUI.
7. Observe that, regardless of how many times you click, what you click, or how fast you click, your input is completely ignored. The only input the game still acknowledges is the location of your mouse cursor, which is rather useless on its own.
Comments 9
It's worth noting that the following appears in my console:
Client> 2013-09-19 21:45:13 [CLIENT] [INFO] Selecting effect minecraft:shaders/post/art.json
Client> 2013-09-19 21:45:13 [CLIENT] [WARNING] Could not find uniform named LumaRamp in the specified shader program.
Client> 2013-09-19 21:45:13 [CLIENT] [WARNING] Could not find uniform named InSize in the specified shader program.This may be specific to my graphics card, then.
Also, I can't reproduce this on my laptop (which has a different card), but it happens very consistently on my desktop.
Didn't help; it still happens on my desktop. As I said, my laptop is fine, so I'm not surprised you can't reproduce it.
Nonetheless, the fact that the game's able to correctly highlight GUI buttons I hover over indicates that this isn't purely a lag issue - it would be nice if it would buffer clicks at least in GUIs where shaders can be changed. Mojang may be able to provide more insight on this - after all, it may be something they can fix, or it may be an LWJGL issue (as LWJGL handles input in addition to rendering).
I'm getting a similar issue only worse using linux 3.2.45 (Slackware 14.0), GeForce 7025 / nForce 630a/ (integrated), x86_64 AMD Athlon II X3 455. Even with post processing disabled and no shaders selected the rendering is very laggy, making movement jerky. The art shader forces fps to drop so low that movement freezes. Buttons are still highlighted though very slowly, but are unresponsive. This seems to be an openGL issue as even the menu screen animation is jerky, though much faster. This snapshot is completely unplayable on my system.
I'm not sure if those warnings mean anything significant. I've been trying to make a custom shader via Resource Packs, and of all the errors those errors didn't seem to actually effect the shaders functioning. It might just be saying the uniform isn't defined yet in the order of loading things. Maybe it is a problem, though, but it doesn't impede the shaders from functioning.
Is this still a concern in the latest Minecraft version 13w48b? If so, please update the affected versions in order to best aid Mojang ensuring bugs are still valid in the latest releases/pre-releases.
Doesn't seem to effect me anymore - although when it hit the first 'TV' shader, it happened for about 20 seconds before finally accepting input. I was able to successfully cycle through all shaders twice. The 'art' shader, which previously caused the lock-up, is no longer that bad. I guess that means this can be closed?
Unable to reproduce. My rendering reduces to about 12fps, but no clicks are ignored.