Scrollbars, part 4: Adding a proportional scrollbar

Raymond ChenJuly 31, 2003Jul 31, 200307/31/03

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.

Answer to yesterday's exercise

Raymond ChenJuly 30, 2003Jul 30, 200307/30/03

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,

Scrollbars, part 3: Optimizing the paint cycle

Raymond ChenJuly 29, 2003Jul 29, 200307/29/03

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 paint rectangle.

Scrollbars, part 2

Raymond ChenJuly 25, 2003Jul 25, 200307/25/03

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,

The scratch program

Raymond ChenJuly 23, 2003Jul 23, 200307/23/03

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.