数组到C ++中的位图

Question

I'd like to create a bitmap by turning an array into a bitmap. First I create the bitmap from the data:

BITMAPINFO info;
info.bmiHeader.biBitCount = 32;
info.bmiHeader.biClrImportant = 0;
info.bmiHeader.biClrUsed = 0;
info.bmiHeader.biCompression = BI_RGB;
info.bmiHeader.biHeight = -height(windowSize);
info.bmiHeader.biPlanes = 1;
info.bmiHeader.biSize = sizeof(BITMAPINFOHEADER);
info.bmiHeader.biSizeImage = 0;
info.bmiHeader.biWidth = width(windowSize);
info.bmiHeader.biXPelsPerMeter = 100;
info.bmiHeader.biYPelsPerMeter = 100;
Gdiplus::Bitmap *b = new Bitmap(&info, (void *)field);

And then I try to draw it on the screen, but it only contains black:

Gdiplus::Graphics *graphics = new Gdiplus::Graphics(hdc);
...
graphics->DrawImage(<pointer to bitmap>, 0, 0);

The array currently contains 32 bits of data per pixel, 8 bits for each component. The red component is shifted 24 bits to the left, green is shifted 16 bits to the left and blue is shifted 8 bits to the left.

I can assure you that the field array contains data in which the colors aren't all black. Does anyone have an idea what I'm doing wrong?

Answer 1

Does the field array last for the whole lifetime of your image? Bitmap constructors that take a pointer to image data will actually store a reference to that data, rather than copying it.

If you want to copy your data and have it stored in the Bitmap object, use NULL for the image bits (or use a constructor that does not require a pointer to image bits), and use the Bitmap.LockBits function to fill in the data. You don't have to copy the bits manually; just fill in the BitmapData structure and use the ImageLockModeWrite|ImageLockModeUserInputBuf flags, and GDI+ will copy the bits by itself.

You may also have better luck with the Bitmap(INT,INT,INT,PixelFormat,BYTE*) constructor (see http://msdn.microsoft.com/en-us/library/ms536315%28v=vs.85%29.aspx ) as it gives you more direct control over how GDI+ will interpret the data (including making it obvious whether your data contains alpha information).