Help on use of Wimp_ForceRedraw

Hi all

I have a question regarding the use of Wimp_ForceRedraw.
At some point in an application I am writing, I want to completely clean the workarea of my main window (wh_main%) and reset the scroll offset to 0, so the top-left hand corner of the visible area coincide with the top-left hand corder of the workarea.
Is the code snippet below correct?

!b% = wh_main%
SYS "Wimp_GetWindowInfo",,b%
b%!20=0:REM scroll x offset relative to work area origin
b%!24=0:REM scroll y offset relative to work area origin
SYS "Wimp_ForceRedraw", !b%,0,0,b%!48 - b%!40,b%!52 - b%!44

Where:
b%!48 – b%!40 = work area maximum x coordinate – work area minimum x coordinate
b%!52 – b%!44 = work area maximum y coordinate – work area minimum y coordinate

so as to invallidate the extent of the workarea…

And a subsidiary question:
Wimp_GetWindowState does not return the work area coordinates, so I use Wimp_GetWindowInfo.
But i feel this is overkill as Wimp_GetWindowInfo returns all the details, including all icons attached to the window, forcing the use of an oversized parameter block “in case of”…
So, is there an alternative way to retreive the work area coordinates which would more sparingly wrt memory?

Thank you for your help.

Regards

François

But i feel this is overkill as Wimp_GetWindowInfo returns all the details, including all icons attached to the window, forcing the use of an oversized parameter block “in case of”…

If you set bit 0 of R1 (pointer to block to contain the info), then only the window header is returned, i.e. the first 88 bytes, without the icon info. You can still recover the number of icons from block!84, and if necessary alloc the required memory before making the full info call.

SYS “Wimp_ForceRedraw”, !b%,0,0,b%!48 – b%!40,b%!52 – b%!44

Remember that y0 is at the bottom of the window and is negative. Therefore I think (without checking) it should be

SYS “Wimp_ForceRedraw”, !b%,0,b%!44 – b%!52,b%!48 – b%!40,0

At some point in an application I am writing, I want to completely clean the workarea of my main window (wh_main%)

You cannot clear the entire workarea of your window using Wimp_ForceRedraw only the visible area.

To reset the scroll offsets you need to call Wimp_OpenWindow with an updated window block. To alter the extent of the work area you use Wimp_SetExtent.

It sounds to me though as if it might be easier to simply open a new instance of your window exactly on top of the old one and then silently delete the old one.

@Chris
Thanks for the tip to retreive the window header only.

@Fred
I am surprised to read that Wimp_ForceRedraw allows to invalidate only the visible area. The PRM Volume 3, chapter 53 says the following

This call forces an area of a window or the screen to be marked as invalid, and to be redrawn later using
Redraw_Window_Request events.
A window handle value of -2 on entry is not available in RISC OS 2.
If R0 is -1 on entry, then R1 – R4 specify an area of the screen in absolute coordinates. If R0 is not -1,
then it indicates a window handle, and R1 – R4 specify an area of the window relative to the window’s
work area origin.

My understanding of the last bit is that, if using a window handle, you invalidate any part of the work area, being visible or not.

I take good note of your remark on Wimp_SetExtent and Wimp_OpenWindow.

Regards

My understanding of the last bit is that, if using a window handle, you invalidate any part of the work area, being visible or not.

Obvious question – how is ForceRedraw supposed to invalidate something that isn’t visible?

My understanding of the last bit is that, if using a window handle, you invalidate any part of the work area, being visible or not.

Yes, you can invalidate an area bigger than the visible area but it’s what happens next that matters.

The Wimp will send you a redraw event as your window falls inside the area invalidated. You can then redraw the window but the Wimp will have set up a clipping rectangle the size of your window’s visible area and anything drawn outside of it will be clipped. Hence you cannot update anything outside the visible area.

It would be useful to know what the window is displaying. If it’s something you redraw yourself then you simply don’t redraw it (the Wimp will have cleared the area to the background colour of the window). If it’s icons then they will need to be removed explicitly by calling Wimp_DeleteIcon.

The main window aims at displaying results from simulations of brownian motion processes. Every time you run a simulation, this invalidates previously displayed results of the whole workarea, not only the visible part of the window. This is why I was thinking to invalidate the whole work area, in order to avoid inconsistent display. But, if i understand well, i can just reset the offset et call Wimp_OpenWindow…

But, if i understand well, i can just reset the offset et call Wimp_OpenWindow…

Yes, that’s okay if you’ve turned off the autoredraw bit in the window flags otherwise you won’t get a redraw event.