Now code looks like this:
Page not displays any buttons and clicks for "next" automatically by timer for post function PROGRESS_LEAVE execution. Where i must put my code for file operations for page not freezes and actually show progress? I not able to use sections there since it is pre-installation tasks.
...
Page custom PROGRESS PROGRESS_LEAVE
...
Function PROGRESS
...
nsDialogs::Create 1018
#hide buttons
GetDlgItem $0 $HWNDPARENT 1
ShowWindow $0 ${SW_HIDE}
GetDlgItem $0 $HWNDPARENT 2
ShowWindow $0 ${SW_HIDE}
GetDlgItem $0 $HWNDPARENT 3
ShowWindow $0 ${SW_HIDE}
...
${NSD_CreateProgressBar} 0u 20u 100% 10u ""
...
${NSD_CreateTimer} OnTimer 1000
nsDialogs::Show
Function OnTimer
Var /Global clicked
StrCmp $clicked "true" progbar
StrCpy $clicked "true"
GetDlgItem $0 $HWNDPARENT 1
SendMessage $0 ${BM_CLICK} 0 0
progbar:
#animation related code here
...
FunctionEnd
Function PROGRESS_LEAVE #a huge timed operations there
...
FunctionEnd