BMP image generated But displayed inverted

Question

I have generated bitmap.dll through winddk.

Added manually as a printer driver selecting print-to-file driver.

Using this I create an image of my document using print command from file.

I am able to create image and view it, But the problem is that I get inverted(mirror) image.

cScans = pOemPDEV->bmInfoHeader.biHeight;
// Flip the biHeight member so that it denotes top-down bitmap 
pOemPDEV->bmInfoHeader.biHeight = cScans * -1;

Have anyone workaround of this code? As I get the problem when I comment(to get header properly generated) this lines.

Answer 1

Device Independent Bitmaps are documented as being laid out in memory with the bottom line at the start of the buffer. Its an experiment in cartesian co-ordinates perpetrated by the designers of OS/2 who were working with Microsoft at the same time Windows 3 was being developed.

There are two possible fixes:

1. Generate your buffer upside down.
2. Many Windows APIs that take a BITMAPINFO treat a negative biHeight value to mean a top down DIB.