Selection optimization

[Terry Foster]

I''ve created a virtual grid and have noticed that the larger the selection that is made, the slower it takes to make the selection. I''m almost certain that this is because QueryCellInfo is being called for at least all of the cells within the selection (although I believe it is also being called for all visible cells on the same rows and same columns as selection, even if it is not in the selection). A good way to demonstrate this is in your Virtual Grid Quick Start sample: maximize the window and then either drag a large selection or click on the top-left corner to select the whole table.

I know there is probably a reason for this, but I''m wondering if you know of a way to disable querying for this type of operation since I never need to provide different cell info based on whether the cell is selected or not. I''ve noticed that the contrast in performance between my virtual grid and Excel is striking and would like to provide my users with better selection response. If there is nothing I can do about this, could this be a potential future optimization option?

Thanks,
Terry

P.S. Using 3.0.1.0 on XP.

[Administrator]

I think a major portion of the delay in teh Quick Start sample is from using Alphablending to draw the selections. You can test this in your application by setting:

this.gridControl1.AllowSelection &= ~GridSelectionFlags.AlphaBlend;

to turn off the alphablending and just have the grid invert teh cells to display the selections. Now depending upon the colors you are using, you will likely not be able to use this technique as teh inverting mainly makes teh selections black. But it should point out whether the delay is due to QueryCellInfo or the the alphablending.

[Terry Foster]

It is indeed the alphablending - MUCH better response when I disabled that in my virtual grid. Unfortunately, as you mentioned, I cannot go with this approach: not only does it look weird (almost downright ugly), but I noticed some serious inversion residual painting issues (probably related to my frozen columns as I''ve had issues related to this in the past with the excel-like selection frame - I can''t get this to happen in your sample). I''m assuming there is nothing to be done to optimize the alphablending, right?

Thanks,
Terry

[Administrator]

Optimizing alpha blending is GDI+ territory, a dominion of MS. I assume it will happen, but don''t know.

There may be something we can do using DrawDirectToDC to speed things up a little, and we can investigate this to see if it makes a dfference at all, but it will take some time for us to get to this. I will make it a feature request to investigate whether using DrawDirectToDC to draw selections speeds things up.

http://www.syncfusion.com/support/features/grid/Default.aspx?ToDo=view&questId=328