Device Contexts and 24-bit Bitmaps

[ASingerMustDie]

Hi Everyone ,

(Incidentally, I also posted this plea in a Microsoft Newsgroup, I hope that doesn't annoy anyone? )

I am having trouble understanding why the following method (invoked when I click the corresponding button in a dialog) is not drawing an image to the screen.

void CMyTestDlg::OnDrawButton()
{
// Array representing a 640 * 480 24-bit bitmap
unsigned char displayImage[640 * 480 * 3];

// Client area of a frame (static) control
CDC *clientDC;
clientDC = GetDlgItem(IDC_DRAW_FRAME)->GetDC();

int pix;
for (int y = 0; y < 480; y++)
{
for (int x = 0; x < 640; x++)
{
// For now I am just setting each RGB (or BGR) component to 50
// until the program works that is
// (Obviously memset would be faster and better otherwise)
pix = (y * 640 * 3) + (x * 3);
displayImage[pix] = 50; // Green
displayImage[pix+1] = 50; // Blue
displayImage[pix+2] = 50; // Red
}
}

BITMAP bm;
bm.bmType = 0;
bm.bmWidth = 640;
bm.bmHeight = 480;
bm.bmWidthBytes = 640 * 3;
bm.bmPlanes = 1;
bm.bmBitsPixel = 24;
bm.bmBits = displayImage;

CBitmap displayBitmap;
displayBitmap.CreateBitmapIndirect(&bm);
// displayBitmap should now be a dark grey 24-bit bitmap

// Create memory based device context and select in the bitmap
CDC MemDC;
MemDC.CreateCompatibleDC(clientDC);
MemDC.SelectObject(&displayBitmap);

// BitBlt the bitmap to the control device context
clientDC->BitBlt(0, 0, bm.bmWidth, bm.bmHeight, &MemDC, 0, 0, SRCCOPY);
}

And what I see is nothing...nothing happens. I have noticed that if I change bm.bmBitsPixel to 16, an image is copied to the control, but it is obviously distorted.

What is the problem?

Thanks much indeed in advance,
Tracy

 

[tchouch]

What is Yor Problem really? Do You wish to show (or learn to show) an image or to understand, why Your method not works?
About Your method: it has very many problems, for example:
1. What is IDC_DRAW_FRAME (if Static: on default Static Control hac Icon Type, not Bmp - Type).
2.SelectObject() uses HBITMAB, not BITMAP! To become such handle, You must create a Bitmap - for that You can use Your displayImage[] as a part of DIB.
3. To show a Bitmap in a Window with BitBlt(), You should override OnDraw() Member Function and use BitBlt() with their DC.
4....
Try to look in MSDN (keyword DIBToBitmap)
or use link:

http://msdn.microsoft.com/code/default.asp?url=/msdn-files/026/000/209/Source Files/Dibutil_cpp.asp