The Old New Thing

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...

Eric's complete guide to BSTR semantics

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

Raymond Chen

Eric Lippert has posted Eric's Complete Guide to BSTR Semantics. This is a document that is widely valued within Microsoft, since BSTR semantics are rather tricky, and I'm glad he's willing to share it with the world. In particular, Eric spends quite a bit of time discussion the very ...

Answers to exercises from Scrollbars Part 10

September 13, 2003 Sep 13, 2003 09/13/03

Raymond Chen

Answers to exercises from Scrollbars Part 10.

Scrollbars part 10 – Towards a deeper understanding of the WM_NCCALCSIZE message

September 11, 2003 Sep 11, 2003 09/11/03

Raymond Chen

When your window is resized, Windows uses the WM_NCCALCSIZE message to determine where your window's client area lives inside your window rectangle. There are two forms of the WM_NCCALCSIZE message. The simple form merely takes a window rectangle and returns a client rectangle. This is useful for...

Scrollbars part 9 – Maintaining the metaphor

September 9, 2003 Sep 9, 2003 09/9/03

Raymond Chen

When a document is displayed with scrollbars, the metaphor is that the window is a viewport onto the entire document, only a portion of which is visible at the moment. The default behavior of a resize, however, is to maintain the origin at the upper left corner of the client area, which breaks the metaphor...