OpenEuphoria

Re: Scaling images

• Posted by Brian Broker <bkb at cnw.com> Nov 22, 2004
• 2333 views

Jonas Temple wrote:
> 
> Since graphics in Windows is my weak spot...how does one scale an image
> (BMP, PNG, JPEG, etc.) such that when the image is shrunk by the user
> it doesn't look funny?  What I mean by "funny" is that I have a window
> that displays an image (using FreeImage).  I want to show the image in
> the window for a "preview" so I use the stretchBlt function in 
> Win32Lib to shrink the image.  But the shrunken image does not look as
> good as say, shrinking the image in the Windows Picture and Fax Viewer in
> XP.
> 
> Can this be done with stretchBlt or is more complicated than that?
> 
> 
> Jonas Temple
> <a href="http://www.yhti.net/~jktemple">http://www.yhti.net/~jktemple</a>
> 

It's a bit more complicated than that if you want an antialiasing effect.
You can do something like this:

-- for antialiasing effect
  hdc = getDC( Win )
  w32Proc(xSetStretchBltMode,{hdc,HALFTONE}) -- HALFTONE = 4
  w32Proc(xSetBrushOrgEx,{hdc,0,0,NULL})
  releaseDC( hdc )

Now your stretchBlt should look better (with antialiasing effect).

Unfortunately, the HALFTONE option is not supported on Windows 95/98/Me.

Declarations for the above functions are:

constant
xSetStretchBltMode =
  registerw32Procedure(gdi32,"SetStretchBltMode",{C_POINTER,C_INT}),
xSetBrushOrgEx =
  registerw32Procedure(gdi32,"SetBrushOrgEx",{C_POINTER,C_INT,C_INT,C_POINTER}),
  HALFTONE = 4

-- Brian