The Old New Thing

Scrollbars redux: Part 12

October 16, 2003 Oct 16, 2003 10/16/03

Raymond Chen

Reader Jeff Miller added Word-style scroll tips to our sample scrollbar program. Here's how he did it: A tracking tooltip is used to display the scroll tip because we don't want the tooltip to do automatic positioning or automatic show/hide. When a tracking scroll occurs (...

Answer to previous exercise about the mythical WM_MOUSEENTER message

October 14, 2003 Oct 14, 2003 10/14/03

Raymond Chen

If the program starts with the mouse already in the client area without moving, why do you get a beep?

Why is there no WM_MOUSEENTER message?

October 13, 2003 Oct 13, 2003 10/13/03

Raymond Chen

There is a WM_MOUSELEAVE message. Why isn't there a WM_MOUSEENTER message? Because you can easily figure that out for yourself. When you receive a WM_MOUSELEAVE message, set a flag that says, "The mouse is outside the window." When you receive a WM_MOUSEMOVE message and the flag...

Other uses for bitmap brushes

October 9, 2003 Oct 9, 2003 10/9/03

Raymond Chen

Bitmap brushes used to be these little 8x8 monochrome patterns that you could use for hatching and maybe little houndstooth patterns if you were really crazy. But you can do better. CreatePatternBrush lets you pass in any old bitmap - even a huge one, and it will create a brush from it. ...

Stupid memory-mapping tricks

October 7, 2003 Oct 7, 2003 10/7/03

Raymond Chen

Shared memory is not just for sharing memory with other processes. It also lets you share memory with yourself in sneaky ways. For example, this sample program (all error checking and cleanup deleted for expository purposes) shows how you can map the same shared memory into two locations ...

Why do I get spurious WM_MOUSEMOVE messages?

October 1, 2003 Oct 1, 2003 10/1/03

Raymond Chen

In order to understand this properly, it helps to know where WM_MOUSEMOVE messages come from. When the hardware mouse reports an interrupt, indicating that the physical mouse has moved, Windows determines which thread should receive the mouse move message and sets a flag on that thread's...

The end of the scrollbar series

September 17, 2003 Sep 17, 2003 09/17/03

Raymond Chen

Okay, that's basically the end of the scrollbar series. Do people actually like the idea of a coding series? It gets very few comments, and it's a lot of work to write, so if nobody actually cares I can just write about quick little things and not try to be coherent from day to day. I guess that's what most blogs are like anyway. If you ...

Answers to exercise from Scrollbars Part 11

September 17, 2003 Sep 17, 2003 09/17/03

Raymond Chen

Exercise: Why do we use the formula c = a + (b-a)/2 instead of the simpler c = (a+b)/2? Answer: To avoid integer overflow in the computation of a+b. Here, a and b are window coordinates, and the window can be anywhere. If the window were placed at extreme coordinates like (...

Scrollbars part 12: Applying WM_NCCALCSIZE to our scrollbar sample

September 17, 2003 Sep 17, 2003 09/17/03

Raymond Chen

Now that we have learned about the intricacies of the WM_NCCALCSIZE message, we can use it to get rid of the flicker in our resizing code. We just take the trick we used above and apply it to the scroll program. First, we need to get rid of the bad flickery resize, so return the ...

Scrollbars part 11: Towards an even deeper understanding of the WM_NCCALCSIZE message

September 15, 2003 Sep 15, 2003 09/15/03

Raymond Chen

The other form of the WM_NCCALCSIZE message is the complicated one, when the WPARAM is TRUE. In this case, the LPARAM is a pointer to a NCCALCSIZE_PARAMS structure. When Windows sends the WM_NCCALCSIZE message, the NCCALCSIZE_PARAMS structure is filled out like this...