[wxPython-users] The grid control -- problems and questions

[Bob Klahn]

Trying again; I fat-fingered my preceding post and sent it prematurely.

At 10:10 PM 9/3/2007, Robin wrote:
>Bob Klahn wrote:
>>The attached grid code features a custom renderer.  In that 
>>renderer, apart from drawing the given cell, I print the row, col, 
>>and isSelected values to stdout, along with the number of the 
>>current call to the draw routine (1, 2, 3, ...).
>>Some questions:
>>     (1) How do I best avoid the excessive drawing that occurs
>>              (a) when switching to another application and switching back?
>>              (b) when resizing the test frame?
>
>Which platform are you on?

Windows XP SP2

>If on the Mac then I think there is code in wxGrid that always 
>redraws all of the visible cells instead of optimizing it down as is 
>done on the other platforms.

It's not optimized here.  wxGrid is redrawing =all= the visible 
cells, both when I resize the test frame, and when I switch to 
another application and switch back.  And if there's a lot of text on 
the screen, I get a good bit of flicker during resizing, and during 
horizontal scrolling.  But no flicker during vertical scrolling, 
which surprises me.

>Otherwise only those cells that intersect with whatever region the 
>OS reports needs to be redrawn are painted.

Then, since many more cells are being redrawn, on my PC at least, 
than the old one and those immediately surrounding it, I guess you're 
telling me that Windows XP is the culprit, that it's telling wxPython 
to redraw several unchanged cells.

>The Grid class doesn't make use of any double buffering at all, and 
>would probably need to be rearchitected to be able to do so, but in 
>practice the method it does use is normally efficient enough.

As I said above, I get a good bit of flicker during resizing and 
horizontal scrolling.  Hmmm, I wonder if I can use Freeze/Thaw and 
only draw during idle time.  That might work for resizing, but

>>     (2) Note the rows that are redrawn as one clicks on different rows.
>>              (a) When one clicks on the row immediately below the 
>> current row,
>>                       (i) notice the color of the rightmost column
>>                               -- Why is that happening?
>>                               -- Why is it different when moving 
>> from row 0 to row 1, versus
>>                                  moving from row n to row n+1 where n <> 0 ?
>
>I don't notice any color problem so I'm not quite sure what you are 
>talking about, but I do notice that you never specify in your 
>renderer's Draw method what the text foreground color should be, so 
>whatever it was set to previously in the DC will be used.  Perhaps 
>that is what you are seeing.

This morning, the code, untouched from yesterday, is not 
demonstrating the color problem.  But you're probably right about 
what I was seeing.  I'll proceed on that basis.

>>                       (ii) notice which rows are redrawn, and in what order
>>                               -- Why so many?
>>              (b) When one clicks on any row not immediately below 
>> the current row,
>>                       (i) notice that the color problem seen above 
>> does not occur
>>                               -- Why not?
>>                       (ii) notice that fewer rows are redrawn
>>                               -- Why?
>
>IIRC, when a new cell selected then the cells around the old one are 
>marked as needing refreshed because the cursor rectangle can overlap 
>the other cells by 1 pixel, so those cells end up getting redrawn to 
>be able to restore the border where the cursor used to be.

That I understand, and that is exactly what's done when I use the 
two-argument CreateGrid call:
         self.CreateGrid( len(data), 2 )

But when I include the selmode argument:
         self.CreateGrid( len(data), 2, gridlib.Grid.SelectRows)
many more cells are redrawn, and I see no reason for that.

By the way, I'm only using wxGrid because I need to support italics, 
subscripts, superscripts, the Greek alphabet, color, etc.
In my real application, the wxGrid will have a single column, i.e., 
conceptually it'll be a list control, but I can't use ListCtrl, as 
you've mentioned in a previous note, because ListCtrl only supports 
plain text.

To me, that seems like a significant gap in wxPython's GUI coverage.

Bob