Re: [Plplot-devel] Am I using eop() or abusing it?

[Jim D. <ji...@di...>]

> On Feb 7, 2016, at 1:44 AM, Greg Jung <gv...@gm...> wrote:
> 
> GDL has had a problem in its use of the wingcc driver in that,
> plotting additions to a basic PLOT call do not stick to the plot
>  when it is moved or resized.  I've found that when I stick another
> eop() call after each of these plot calls, the problem is "solved"
> for this driver https://sourceforge.net/p/gnudatalanguage/bugs/689/#b1d7 <https://sourceforge.net/p/gnudatalanguage/bugs/689/#b1d7>
> because each eop() in wingcc induces another copy of the screen to the 
>  bitmap used for refresh.
> 
>   Jim's new wingdi driver doesn't have this issue although I can't see why not.
> 

What is happening is that plplot is generating the bitmap used for redraws before your GDL additions to the window.  The second EOP call is forcing the creation of a new bitmap, which has the GDL additions.

The new wingdi has a much more robust handling of redraws and resizes, primarily because it closely follows the Windows API documentation. I remember that the wingcc driver was not very smart about creating the bitmap and I had to crack open the documentation on how to do it the “right” (where “right” is relative to the Windows API and not PLplot’s state).  What I think is happening in the wingdi driver is that the additional draws are triggering a new bitmap independent of the EOP call.

> According to the plplot-5.10 doc, eop() would close a plot file begun when bop()
> is called.  Currently rdbuf_eop() is a no-op although there is an EOP code put 
> into the plot buffer.

A lot of the EOP handling happens outside of the rdbuf_eop(), which is why that function is a no-op.

> 
> My happy answer would be that a second eop() without bop() indicates a re-open, "append" to the ongoing plot buffer (or file).  Is that consistent with current usage?

For an interactive driver like wingcc and xwin, I think the primary problem is that you would lose everything after the first EOP when the buffer is replayed.  That can happen in the wingcc driver in a WM_PAINT message if plplot is waiting for input and there is not a valid bitmap for a redraw.  You may be fortunate that the second EOP is creating a valid bitmap, thus avoiding the buffer playback.

> Thanks, 
> Greg
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