Article: Q68569
Product(s): Microsoft Windows Software Development Kit
Version(s): WINDOWS:3.0,3.1
Operating System(s):
Keyword(s): kbfile kbsample kb16bitonly kbOSWin310 kbOSWin300
Last Modified: 05-DEC-1999
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The information in this article applies to:
- Microsoft Windows Software Development Kit (SDK) versions 3.0, 3.1
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SUMMARY
=======
The following information describes a procedure to smoothly drag the window
frame; this procedure is similar to the one that Windows uses when a window is
moved by dragging its caption bar. When the user moves a window with the mouse
or with the keyboard, Windows shows the movement of the window by a moving a
gray-patterned frame. The dragging looks smooth because Windows updates only the
portions of the frame that need to be erased or drawn, leaving all other areas
untouched.
One technique to implement smooth dragging for a single rectangle is described
below. An actual frame in Windows consists of four thin rectangles dragged
together.
MORE INFORMATION
================
The following files are available for download from the Microsoft Download
Center:
Dragrect.exe
For additional information about how to download Microsoft Support files, click
the article number below to view the article in the Microsoft Knowledge Base:
Q119591 How to Obtain Microsoft Support Files from Online Services
Microsoft used the most current virus detection software available on the date of
posting to scan this file for viruses. Once posted, the file is housed on secure
servers that prevent any unauthorized changes to the file.
To smoothly drag a rectangle, redraw only the invalid portions of the rectangle.
For example, if a rectangle is dragged up by 3 pixels, only the top 3 pixels
need to be drawn and the bottom 3 pixels erased. All other parts of the
rectangle are left alone. The same principle applies when a rectangle is moved
on a diagonal--two edges are drawn, two edges are erased, and the bulk of the
middle of the rectangle remains the same.
To implement smooth dragging of a single solid rectangle, perform the following
eight steps:
1. When dragging begins, save the coordinates of the rectangle.
2. Draw the initial rectangle using a pattern brush and the PatBlt function.
Windows uses its own gray brush made with a bitmap of alternating 0x55 and
0xAA values. In the PatBlt call, use the PATINVERT option to combine the
pattern brush and the screen using the XOR operation. The XOR option is very
convenient because another XOR operation restores the screen to its original
state.
Alternatively, use the DSTINVERT option, which performs a NOT operation on the
destination rectangle, ignoring the current selected brush. A second NOT
operation restores the screen to its original state. A NOT operation is
slightly faster than an XOR operation; however, it is not nearly as flexible
with respect to the nature of the rectangle drawn.
3. Each time the mouse is moved, save the new coordinates. The old coordinates
must be retained for the time being.
4. Create an intersection rectangle of the old and new positions using the
IntersectRect function. If this rectangle is empty, call the PatBlt function
twice: to erase the old rectangle and to draw the new rectangle. This is
allowed because the old and new positions have no overlapping region.
5. If the two rectangles intersect, update only the nonoverlapping regions--the
edges of the old and new rectangles that are not in the intersection.
6. In most cases, the rectangle moves in both horizontal and vertical
directions, which creates two regions that need updating:
XXXXXXXXXXXX The union of X, x, and . is the original
XXXXXXXXXXXX rectangle.
x...........o The union of O, o, and . is the new rectangle.
x...........o
x...........o Erase the areas marked with an X or x.
x...........o Draw the areas marked with an O or o.
x...........o
OOOOOOOOOOOO
OOOOOOOOOOOO
7. Each update region contains two smaller rectangles: one that makes up the
horizontal section along the top (marked with uppercase characters in the
diagram above) and one that makes up the vertical section along the side
(marked with lowercase characters).
Once the application determines the coordinates of these rectangles, call the
PatBlt function to draw or erase them as appropriate. Do not draw overlapping
areas twice; that is, when dealing with areas marked x or o, do not draw in
the areas marked X or O, or vice versa.
At this point, the rectangle has been moved without affecting the intersecting
region (marked with periods) at all. Because the intersection was not erased
or drawn, no flicker occurs and the dragging appears smooth.
8. When dragging stops (the mouse button is released), call the PatBlt function
to erase the current rectangle because it is no longer needed.
When a window is moved by dragging the caption bar, Windows divides the window's
rectangle into four parts: the bottom, top, left, and right lines. Each line is
a rectangle because the border of a window is usually thicker than one pixel.
The dragging process above is applied to all of these rectangles at the same
time.
The DRAGRECT sample program available in the Microsoft Software Library
demonstrates the dragging process for both a single rectangle and a frame made
of four separate rectangles. Note that the sample program is not optimized to
drag a frame with the same efficiency as Windows; it is meant only to
demonstrate the concepts involved.
Additional query words: softlib DRAGRECT.EXE
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Keywords : kbfile kbsample kb16bitonly kbOSWin310 kbOSWin300
Technology : kbAudDeveloper kbWin3xSearch kbSDKSearch kbWinSDKSearch kbWinSDK300 kbWinSDK310
Version : WINDOWS:3.0,3.1
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