Now, I'm not suggesting a fully-blown iPad TPT; I've heard that before and seen it rejected a lot.
However, it should be very possible to write an app to just view files and maybe browse them on an iPad.
I've actually researched app development, and it seems like it should be very possible and even easy if you know your way around TPT source.
Interface:
Buttons on the bottom accessing the different display modes (on a Retina display, you could easily fit a TPT save at 2x size with room to spare)
Maybe buttons to control Newtonian gravity, grid, pressure mode, etc if there was room
Maybe a file open/save to computer button
All of these buttons, if not visible by default, could be accessed by swiping up.
Also, it would be quite possible to cycle through display modes by swiping left or right.
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I know the following suggestions well within the realm of impossibility and not nearly as implementable, but I might as well include them anyways:
Possible simulation editing:
3-finger swipe to cycle through brush shapes
2-finger pinch to change brush size
Tap and draw to...well, draw
2-finger swipe left to undo
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I understand that the sim-editing suggestions probably won't even be a possibility, but it would be really great if you could at least consider the first section-I'm very sure it could at least function, and possibly even work faster than a desktop Powder Toy.
I'll be posting images of a possible interface later today, or if not, within a week.
By the way, now that I look at this from outside the thread, I realize that this thread should be in Suggestions; if any moderators have spare time that they don't need for anything else, it would be great if they could move it.
Actually, it wouldn't take any more memory than TPT on a computer.
And there shouldn't be any need to ask for it to be free, TPT is open-source anyways, remember?
I don't think any of the devs have a mac to program the thing on (because apple won't accept code not compiled on a mac), and if they did I don't know if they would be willing to pay the 99$ a year required for the devkit just for this one app.
An android app might be interesting though.
Do you think it is easy?
Would you do it by yourself if it is easy?
Maybe it would be neat, you can gather several TPT members that understand how to code it instead of calling developers here, it will work much more better. After you have done you may ask @Simon to put it as an offical version, this is the best way. Asking developers isn't the right way at all, they're busy with other things such as their own mod, fix TPT bugs, they might not have time for your App.