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Frequently Asked Questions

Raster operations.

Question:

When using a canvas, the return value from the pixels property returns an invalid color of -1 or hex $FFFFFFFF. How can I get around this?

Answer:

This can happen if the requested pixel is not in the 

current clipping region. This can also happen on devices 

that do not support the Windows API functions GetPixel() 

and SetPixel(). You should check the return value from 

the GetDeviceCaps() to check to see if a device supports 

raster operations before using these functions. A printer 

and/or metafile canvas is a likley candidate for a device 

that the pixels property may fail on.



Example:



if (GetDeviceCaps(Printer.Canvas.Handle, RASTERCAPS) 

  and RC_NONE) = RC_NONE then

NoRasterOperations := True;



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PFPhotoFile