CODEWITHSUNDEEP
winapibuffergdi
user1092719
user1092719

Reputation: 523

Accessing GDI drawing context pixels directly

I want to read and write pixels directly from/to a drawing context, i.e. during a paint operation on a window.

I understand that there are GetPixel/SetPixel functions in Windows GDI, but for big operations it would be far better to be able to read and write pixel data directly to memory.

How can I do this using standard GDI?

Upvotes: 6

Views: 1941

Answers (2)

user541686
user541686

Reputation: 210755

Use GetObject to get the BITMAP struct which contains a pointer to the bitmap's data.

Upvotes: 2

Grigorii Chudnov
Grigorii Chudnov

Reputation: 3112

You could create a compatible DC, Bitmap:

HDC     hMemDC = CreateCompatibleDC(hdc);
HBITMAP hBmp   = CreateCompatibleBitmap(hdc, WIDTH, HEIGHT);
SelectObject(hMemDC, hBmp);

Next, there is GetDIBits function you can use to get bits:

int GetDIBits(
  _In_     HDC hdc,
  _In_     HBITMAP hbmp,
  _In_     UINT uStartScan,
  _In_     UINT cScanLines,
  _Out_    LPVOID lpvBits,
  _Inout_  LPBITMAPINFO lpbi,
  _In_     UINT uUsage
);

NOTE: You might need to set lpvBits to NULL to get the dimensions and format of the image via BITMAPINFO (lpbi parameter).

Upvotes: 4

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