If you look at the WM_VSCROLL message, you'll see that the scroll position is a 16-bit value. So if the number of entries is more then 65535, you won't be able to use the scroll thumb to get to the ones at the end. Try it: Change the value of g_cItems to 100000 and watch what happens. The fix is to ignore the passed to the message and instead ge...

To obtain a proportional scrollbar, you need to tell Windows the minimum and maximum values covered by the scrollbar, the current scrollbar position, and the size of the scrollbar thumb (called the "page size"). One annoyance of the way scrollbars are set up is that the maximum value is attainable. This differs...

iMin is the lowest-index element which intersects the paint rectangle, so a simple truncating division produces the desired index. The formula for iMax can be interpreted two ways. One is that it is the roundup of the first invisible line. Recall the rectangles are exclusive of the endpoint, s...

Common request: I want to be able to turn on personalized menus (Intellimenus) when in XP Start Menu mode. Imagine if Intellimenus were enabled with the XP Start Menu. You use 5 apps; the rest are not used much. (Studies show that 5 is the typical number of unique applications us...

Observe that we paint all 100 lines in our paint handler, even though most of them aren't visible. This is a problem if there are a large number of items, or if painting an item is time-consuming. So instead, we optimize our paint cycle so as to paint only the elements which intersect the pain...

We often get requests like this: There should be a slider bar somewhere, say on the Performance Tab, that ranges from Novice to Advanced. At the highest level, all the geek settings are turned on. At the Novice level, all the settings for beginners are turned on. In between, we can gradually enable stuff. ...

Managing scrollbars is not hard in principle. The basic idea is not that difficult, but there are a lot of small details that need to be ironed out. If you don't get the details just right, your program will feel odd in a strange way that you often can't pinpoint, much like a subtle background hum that makes yo...

I'm going to try to alternate between programming entries (where I actually try to teach something) and random entries (where I get to spout off or go into storytelling mode). So here's another random entry. Why does Tweak UI put up a totally incomprehensible error message ("Cannot locate ...

Occasionally, there is need to illustrate a point with a full program. To avoid reproducing the boring parts of the program, let's agree on using the following template for our sample programs. For expository purposes, I won't use a C++ class. I'll just keep all my variables global. In a real program, of course, instance data would be attached to ...

Short answer: The same reason you turn the ignition key to shut off your car. Long answer: Back in the early days, the taskbar didn't have a Start button. (In a future history column, you'll learn that back in the early days, the taskbar wasn't called the taskbar.) Instead of the S...