How To Draw on a Memory Bitmap in GDI+

Summary

You may sometimes want to obtain a bitmap or image that contains the image that was drawn by a graphics object.

One of the overloaded constructors for the Bitmap class takes a graphics object as a parameter. However, this constructor does not use the image drawn by the graphics object to initialize the bitmap bits. It simply creates a bitmap with properties similar to the graphics object, such as dots per inch.

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Because the Bitmap constructor does not initialize the image bits by using the image from the graphics object, code like the following will NOT result in a bitmap that contains the image that was drawn by the Graphics object:

Graphics g( hWnd );
// Draw on g
Bitmap b( 100, 100, &g ); // Will not get image from g

To use a graphics object to draw on a bitmap, code like the following can be used instead:

Bitmap b(100,100);
Graphics *g = Graphics::FromImage(&b);
// Draw on g

To capture the preexisting image from a window, a Windows Graphics Device Interface (GDI) function such as BitBlt() or StretchBlt() would have to be used to copy the image from the screen to a memory bitmap. This memory bitmap could then be used in the overloaded Bitmap constructor, which takes an HBITMAP as a parameter.

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References

For additional information on capturing the screen using GDI, click the article number below to view the article in the Microsoft Knowledge Base:

186736 How To Capture and Print an Entire Window

"Capturing an Image" in the GDI section of the Platform SDK Documentation:

http://msdn.microsoft.com/en-us/library/dd183402(VS.85).aspx

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Keywords: kb, kbbillprodsweep, kbhowto, kbdsupport, kbdswgdi2003swept, kbgdi64swept

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Article Info

Article ID	:	299583
Revision	:	5
Created on	:	8/20/2020
Published on	:	8/20/2020
Exists online	:	False
Views	:	133

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How To Draw on a Memory Bitmap in GDI+

Summary

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References