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Drawing Bitmaps

Posted on 2004-04-29
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Last Modified: 2011-04-14
Hi Guys,

Can someone please write some example code to draw a bitmap to the screen in a simple window.  This bitmap must be created in memory (i.e. not from a file) and allow me to write individual pixels to it.  I'm trying to test the speed of gdi vs java 2d.  I have some generic algorithms that i want to port to C++ but I need the above to do it.

Kind Regards,

Chris
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Question by:chrisevans123
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George Tokas earned 125 total points
ID: 10952675
In BCB:
Drop a TImage at your form.
Use the following:
TMemoryStream   *MemStream;
Graphics::TBitmap *MyBitmap;
MemStream = new TMemStream;
ThePicture = new Graphics::TBitmap;
MemStream->LoadFromFile("myBitmap");
ThePicture->LoadFromStream(MemStream);
Now you have the bitmap loaded at MemStream(RAM Handle) and also at ThePicture which is a Bitmap allocated buffer.
Using:
TImage(the name of the control on the form)->Picture->Assign(ThePicture);
Display the Bitmap.
You can manipulate ThePicture(Bitmap) and save reload or anything you like.
VC++ is a bit different.

Regards,
gtokas.
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LVL 48

Assisted Solution

by:AlexFM
AlexFM earned 125 total points
ID: 10958314
The simplest (and well-performing) way to draw bitmap created in memory is using of StretchDIBits function. To use this function you need:

1) Fill BITMAPINFO structure with bitmap parameters (you can use standard RGB bitmap with biBitCount = 24), without color palette.
2) Create array with size 3*w*h bytes (w and h are bitamp width and height). Fill it by some way, setting appropriate R,G and B values (color order in memory is BGR).
3) Call StretchDIBits function to draw bitmap to window device context.
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