I’m currently implementing a software keyboard ( using some sophisticated prediction ), and drawing it using canvas is insufficient in terms of perfomance. I’m getting frame drawing times well above 100ms, which is clearly unacceptable.
The keyboard itself consists of about 33 keys, each of them drawn using drawRoundRect and a simple Text above that. No widgets whatsoever are used, so it’s the plain perfomance. Also, almost all of Googles perfomance tips are in use, so thats not the reason for the speed either.
I’ve now reached a point where switching to opengl actually would make sense, but I’m still sceptical considering the impact an opengl-based keyboard might have on battery life.
As I’ve found no sufficient documentation on that topic, I hope someone here can point me to the right direction.
Regardless of how much it drains the battery, you probably don’t want to do this because most existing devices don’t support multiple OpenGL contexts at the same time, so your soft keyboard would be incompatible with any application that is using OpenGL for its own drawing. On these devices the OpenGL context is owned only by the foreground application; it can not be used in secondary parts of the UI like the soft keyboard.
Also as the previous poster said, you would probably be best off looking how to optimize your regular drawing. Drawing vectors is quite slow, so pre-rendering them into a bitmap to just do bitmap blits would help a lot. Also be careful to only draw the parts of the window that have changed. 100ms is a pretty insane amount of time to take to draw the UI, so there are almost certainly significant optimizations you can make. You might want to look at the KeyboardView code in the platform (which is used by the standard soft keyboard and sample IME); this already contains many similar drawing optimizations.