This is open source:
https://github.com/markusfisch/ShaderEditor

* Live preview in background or on an extra screen
* Syntax highlighting
* Error highlighting
* FPS display
* Use any shader as live wallpaper
* Exposure of hardware sensors
* Support for wallpaper offset
* Exposure of battery level
* Supports multiple touches
* Previous rendered frame in backbuffer texture
* Import and use arbitrary textures
* Disables rendering when battery is low

Some devices limit GPU usage to consume less power when not plugged in. Always check the performance with the soft keyboard hidden and the power cord off. A shader should make at least around 30 fps to not slow down the UI if you intend to use it as a live wallpaper.

Unfortunately error information is disabled on some devices (e.g. Huawei Ideos X3, Asus Transformer). Error highlighting/reporting is not possible on these devices.

Please report bugs here:
https://github.com/markusfisch/ShaderEditor/issues