There are many tutorials over
the internet about the BitBlt API call. This is one of the most
important functions used by
graphics/game programmers, so I decided VB Center should have one about
it too.
The BitBlt function resides in GDI32 (graphics device interface), a dll that is usually located at your system path. It is used to print rectangular blocks of pixels from a source image (that can be either in a picture box or stored at a memory DC) to a destination (the same thing).
Well, if you didn't understand too much, just think of BitBlt as a function similar to PaintPicture - but with much more effects and velocity.
To call this function from VB, add the following code to the declarations section of a module:
Declare Function BitBlt Lib "gdi32" Alias "BitBlt" (ByVal hDestDC As Long, ByVal x As Long, ByVal y As Long, ByVal nWidth As Long, ByVal nHeight As Long, ByVal hSrcDC As Long, ByVal xSrc As Long, ByVal ySrc As Long, ByVal dwRop As Long) As Long
' ================================
'PARAMETERS
AND THEIR DESCRIPTION
' ================================
' ByVal
hDestDC As Long ..... hDC of object to receive the .bmp
' ByVal
x As Long ........... x coordinate (upper-left) destination rectangle
' ByVal
y As Long ........... y coordinate (upper-left) destination rectangle
' ByVal
nWidth As Long ...... width of the destination rect. and source .bmp
' ByVal
nHeight As Long ..... height of the destination rect. and source .bmp
' ByVal
hSrcDC As Long ...... hDC of source object that contains the .bmp
' ByVal
xSrc As Long ........ x coordinate (upper-left) source .bmp
' ByVal
ySrc As Long ........ y coordinate (upper-left) source .bmp
' ByVal
dwRop As Long ....... specifies the raster operation to be performed
Here it is! Now that you have declared the function, add some constants to the raster operations you'll use:
Public Const SRCCOPY = &HCC0020 'Copies the source bitmap to destination bitmap.
Public Const SRCAND
= &H8800C6
'Combines pixels of the destination with source bitmap
'using the Boolean AND operator.
Public Const SRCINVERT
= &H660046 'Combines pixels of the
destionation with the bitmap
'using the Boolean XOR operator.
Public Const SRCPAINT
= &HEE0086 'Combines
pixels of the destination with source bitmap
'using the Boolean OR operator.
Public Const SRCERASE
= &H4400328 'Inverts the destination
bitmap and then combines the
'results with the source bitmap using the Boolean AND
'operator
Public Const DSINVERT = &H550009 'Inverts the destination bitmap.
Public Const NOTSRCCOPY = &H330008 'Copies the inverted source bitmap to the dest.
Public
Const NOTSRCERASE
= &H1100A6 'Inverts the result of combining
the destination and
'source bitmap using the Boolean OR operator.
Public
Const MERGECOPY
= &HC000CA 'Combines the pattern
and the source bitmap using
'the Boolean AND operation.
Public
Const MERGEPAINT = &HBB0226
'Combines the inverted source bitmap with the
'destination bitmap using the Boolean OR operator.
Public
Const PATCOPY = &HF00021
'Copies the pattern to the destination bitmap.
Public
Const PATINVERT
= &H5A0049 'Combines the destination
bitmap with the pattern
'using the Boolean XOR operator.
Public
Const PATPAINT
= &HFB0A09 'Combines
the inverted source bitmap with the pattern
'using the Boolean OR operator. Combines the result of
'this operation with the destination bitmap using the
'Boolean OR operator.
Public Const WHITENESS = &HFF0062 'Turns all output white.
Public Const BLACKNESS = &H42 'Turn output black.
With this you have all the possibilities that can be used with the BitBlt function. Now we can proceed...
If you examined the code well, you must have noticed two little tricky parameters: hDestDC and hSrcDC.
These properties are handles Windows use to identify where are the source and destination pixels. Device Contexts are utilized in almost all API calls - just take a look over VB Center and you'll see other functions that use DCs.
Forms and PictureBoxes already have their hDC property so that you can perform graphics-related functions.
Ok. So when you use BitBlt, it will be like this:
BitBlt to Destination.hDC , (additional parameters), from Source.hDC
Another thing: you must set your Forms and PictureBoxes AutoRedraw property to True, and after you blit, Refresh your control (object.Refresh).
The best way to learn is looking
at examples, so pay attention to the following:
| This image shows
you how BitBlt works. Here we have a source picture, Picture1, and
a destination picture (Picture2). We want to blit only the third
cell to the scenery - it has 64x64 pixels and is located at the coordinate
0,128 inside Picture1. Oh, and our hero must be at the coordinate 70, 200
in the scenery.
So we use the code at the picture! It's like: BitBlt to Picture2, at 70, 200, width/height: 64,64, from Picture1, at 0, 128, raster operation To acheive transparency, SRCCOPY is not used... But this is just and example! :^) |
 |
Look at the example above with attention. I'm sure you understand something!
If you have any questions, e-mail me!
Check our tutorial on acheiving transparency and on the creation of DCs soon!
