What am i doing wrong?

[TpOreilly]

Well, adding to the update region...

And, is the update region by default set to null?

[Lamblion]

http://msdn.microsoft.com/en-us/library/dd145002(v=VS.85).aspx

http://msdn.microsoft.com/en-us/library/dd145167(v=VS.85).aspx

Basically, UpdateWindow() doesn't know anything has changed unless you InvalideRect() it.

[TpOreilly]

Thanks, is the update region by default set to null?

[Lamblion]

I don't know if it is literally set to NULL, but I do know that if the client area of the window is empty then UpdateWindow() will return FALSE.

Again, you must understand that you are dealing with two DIFFERENT objects here.

[TpOreilly]

thanks

[anonymous23323124]

Lamblion wrote:

UpdateWindow() merely updates the window attributes and corroborating sysmtem parameters.

Are you sure? This is what I read:

MSDN wrote:

The UpdateWindow function updates the client area of the specified window by sending a WM_PAINT message to the window if the window's update region is not empty. The function sends a WM_PAINT message directly to the window procedure of the specified window, bypassing the application queue. If the update region is empty, no message is sent.

Lamblion wrote:

InvalidateRect() erases and then redraws the specified rectangle within the window itself, assuming you've WM_PAINT or other such functions to do the redraw.

Or does it mark the rectangle for redrawing, and then leave the OS to have it redrawn:

MSDN wrote:

The invalidated areas accumulate in the update region until the region is processed when the next WM_PAINT message occurs or until the region is validated by using the ValidateRect or ValidateRgn function.

The system sends a WM_PAINT message to a window whenever its update region is not empty and there are no other messages in the application queue for that window.

Tporeilly wrote:

update region by default set to null?

NULL is a pointer thing, so I doubt the actual update region is set to NULL. However, I should guess it would be empty following a paint operation. Then it will remain empty until you invalidate it, or until the system invalidates it due to a resize or something.

[Lamblion]

My first statement is merely a basic paraphrase of what you read. If the window parameters aren't altered, then no message is sent, just like it says.

Again, my statement on InvalidateRect() is just a basic paraphrase of what happens, and it in no way contradicts the MSDN statement. . I had no intention of getting into techical step-by-step detail of exactly how it works.

That's why I suggested reading Petzold. InvalidateRect() must invalidate the specified rectangle and then send the appropriate message to Windows so that WM_PAINT or other such calls can then perform the desired action. No, InvalidateRect() doesn't actually do the redraw itself, and I didn't mean to to imply that in the statement, which is why I added the qualifier.

The best thing to do is read the MSDN links and follow the further links to understand the technical step-by-step actions that are performed, although even MSDN won't given you all of that info. You need Petzold and Richter and other outside sources for that.

[Lamblion]

This may help explain it. From Petzold --

"Your window procedure receives a WM_PAINT message ONLY if part of your client area is invalid." Petzold, p 74, 5th Edition Programming Windows

UpdateWindow() obviously does NOT invalidate any of the client area, and thus no new WM_PAINT message will be sent because Windows doesn't know that any parameters of the window have changed.

[TpOreilly]

Thanks :)

[anonymous23323124]

UpdateWindow() will, of course, cause a WM_PAINT message to be dispatched if the update region is already non empty.

@Lamblion Fair enough. I think I misunderstood what you meant by "window parameters" :)

[Lamblion]

Well, I'm not the most solid person when it comes to programming terms, so "parameters" may not even be the right word, but it was the best I could do at the moment. -:)