Visual Basic 6’s PaintPicture method
allows you to create special effects with bitmap images. You must start with a
source picture, which can be an image in either a Picture Box control or on a
form. Then, you can take all or part of that picture—any rectangular region, in
fact—and place it anywhere you desire on another Picture Box or form, or on the
source Picture Box or form. You have numerous options as to how the copied
image is combined with any image that already exists in the destination. In
addition, you can stretch or shrink the “copied” picture.
Here are the arguments of the PaintPicture
object.PaintPicture source, x1, y1, w1, h1, x2, y2, w2, h2, opcode
- object: The name of the Picture Box,
Form, or Printer object where the picture is to be placed. This argument
is optional. If it’s omitted, the form with the focus is assumed.
- source: The source of the graphic. It
must be the Picture property of a Form or Picture Box object.
- x1, y1: Single-precision values
indicating the destination coordinates (in other words, the location on
the destination object where the top-left corner of the image is to be
drawn). The ScaleMode property of the object
determines the unit of measure used.
- w1, h1: Single-precision values
indicating the destination width and height of the picture, using units
specified by the ScaleMode property of the
destination object. If the destination width and/or height is larger or smaller than the source width (w2) or
height (h2), the picture is stretched or compressed to fit. These
arguments are optional; if you omit them, the source width (w1) and height
(h1) are used with no stretching or compression.
- x2, y2: Single-precision values
indicating the source coordinates of the region in the source object that
is to be copied (in units specified by the source object’s ScaleMode property). These arguments are optional; if you
omit them, 0 is assumed (indicating the top-left corner of the source
- w2, h2: Single-precision values
indicating the width and height of the region within the source that is to
be copied (in units specified by the source object’s ScaleMode
property). These arguments are optional; if you omit them, the entire source width and height are used.
- opcode: A type Long value that defines
the bit-wise operation that is performed between the pixels of the source
picture and the pixels of any existing image on the destination. This
argument, which is optional, is useful only with bitmaps. If you omit the
argument, the source is copied onto the destination, replacing anything
that is there.
Think of the source picture as being printed on a rubber
sheet. You can cut out any rectangular part of the picture you want, stretch it
vertically and/or horizontally, and stick it down anywhere on the destination
Making sense of opcode
The opcode argument can be a bit
confusing because there are dozens of ways that you can copy a picture from one
location to another. Here are more details about how it works.
In the destination object, where the copied picture is going
to be placed, an image already exists. A bitmap picture may be displayed there
already, but even if the destination is blank, something is there—perhaps just
white pixels. Over the extent of the copied region, for each pixel in the
copied image there is a corresponding pixel at the same location in the
destination. How will these pixels be combined? This is what the opcode argument determines.
The simplest (and perhaps most common) operation is to have
each new pixel replace the original pixel. The opcode
argument for this is the predefined constant vbSrcCopy.
Other opcode arguments perform a variety of logical
combinations of the source picture with the destination picture. These can be
used to create certain types of visual effects, but I won’t go into them here. You
can explore the topic further in the Visual Basic Help system.
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