Measure widget according to desired width and height constraints. (Step 1 of two phase layout).
Draw widget at its position to buffer
Set current progress value, 0 .. 1000; -1 == indeterminate, -2 == hidden
Get current progress value, 0 .. 1000; -1 == indeterminate
returns true if progress bar is in indeterminate state
get animation interval in milliseconds, if 0 - no animation
set animation interval in milliseconds, if 0 - no animation
called on animation timer
handle timer; return true to repeat timer event after next interval, false cancel timer
Progress bar widget