Re: Image transformations

[Eli Zaretskii]

> Date: Thu, 13 Jun 2019 17:58:04 +0100
> From: Alan Third <address@hidden>
> Cc: address@hidden
> 
> Can you point me to the Windows API documentation and perhaps I can
> work out how exactly we need to approach this?

I want to use PlgBlt, see

  https://docs.microsoft.com/en-us/windows/desktop/api/wingdi/nf-wingdi-plgblt

For that, I need to compute, for each of the original image's
vertices, the coordinates of the corresponding vertex of the
transformed image.  That's why I was asking how to interpret the
matrix elements for transforming pixel coordinates.

I also want to know when no rotation is involved, so that I could use
the existing code (which only supports scaling and will be modified to
support cropping) on older Windows versions that cannot support
rotations (PlgBlt is not available on those platforms).

Thanks.