I've done more checking on my S7 and it seems that reloading any save, even one which loads correctly at first or one made by saving to disk (without closing and loading again), by clicking the reload button causes the same effect. Also, even an empty save made with save to disk will not load.
Additionally, I've done more testing with the AVDs, and I've found something which could be usefull - if I change the CPU of the Nexus 5 device to an "armeabi-v7a" causes the app to correctly load and reload any saves, whilst this is not the case for the "x86" and"x86_64" CPU types (saves crash on these CPUs). Perhaps this difference could be of use.
"I'm not actually an Android device though" - jacob2. Of course you aren't.
Sorry. I made some mistakes in my last post, but I have found something very useful.
(this info is all for the S7 device, haven't had a chance to check with the emulator yet)
Firstly, it looks like reloading saves which loaded correctly at first does work (I thought I checked that, but it seems I didn't).
Secondly, and much more importantly, the "empty save" which I thought was empty when testing wasn't actually completely empty - I forgot about the walls!! Making a save (blank or with particles) with a type of wall in it and reloading it causes the crash, while a save without wall in it loads fine.
THAT SEEMS TO BE THE DIFFERENCE BETWEEN THE CRASHING AND NOT CRASHING SAVES - WALLS SEEM TO BE CAUSING THE CRASHES!!!
I hope this helps.
Edit: also, would it be possible to make the save location changeable (as the app currently saves to and loads from a location which is not visible to me, so I can't copy saves from or to the device), and also make it so that this app is set to be able to open powder toy save (.cps) files as I currently can't open saves I copy to the device (this wouldn't be necessary if the save location was changeable but would be nice, I can't set the app as the defaut to open these files unless the app is set to be able to open that file type. I found some stuff here on that: http://stackoverflow.com/questions/9872450/make-your-app-a-default-app-to-open-a-certain-file). Sorry for such a long post.
Edit2: an app I found lists CPU ABI for my samsung S7 as arm64-v8a, so not sure what this means for the CPU types it works on, but it does say 64 and v8a unlike the CPU for the emulator on which it works, I'll check this on my other devices.
Edit3: My other devices (Galaxy Ace 2 and Galaxy Tab 3, on which the app works fine) list as armeabi-v7a under the same app, the same as the one which worked in the emulator. Maybe it only works on this. Also, I checked and in the emulator the behaviour is the same - the crash is caused by loading a save containing walls of any type.
On compiling I would be happy to try to help, but I'm not sure how much I would be able to do (I've had mixed amounts of success in compiling stuff before).
Maybe could add a on screen mouse, which is controlled in a way that moving on screen acts as a touchpad and moves the mouse, instead of shaping it to where they are tapping. Can add more precision, and is easier to see what you are doing, because you don't have a finger in the way of your view.
If you don't really knowwhat I mean, try using teamviewer on android.
Also, you could maybe add the buttons to be in the gaps on the edges of the screen that are normally just black, because of powdertoy's aspect ratio being less than the phones.
Other than that it is great app! Works really well on my fake S5, and on the android mini PC.
I've suggested that great idea to jacob1 for the reasons you stated and also because it will let users see the properties of elements without altering them (eg ctype). He said "Interesting idea. The SDL port has a setting for that which I tried using once but it isn't very easy tp hit buttons that way. I'll see if I can toggle it from in game." So we might see it in the future. Right now, he is trying to get all the stuff he needs to develop the android version again as he lost those when he returned his school laptop. Hopefully he gets it all again and this idea gets added as it would make it way more convenient to use the android version.
Other ideas for android that I think would be really useful:
Undo button
Better (actual) buttons to move/rotate/flip stamps as the one used currently as really finnicky
Advance by one frame button
Some way to lengthen/shorten cursor horizontally/vertically like in pc
Fixed newtonian gravity
Way to access line tool and drag-to-make-rectangles tool
Fill-in tool