[fpc-pascal] Performance problems with Image Conversions

[Sven Barth]

On 24.02.2013 11:44, Michael Van Canneyt wrote:
>>      srcImg:=TFPMemoryImage.Create(0,0);
>
> Do not use TFPMemoryImage. It is a catch-all memory format, not
> optimized at all, using 64 bits for the images.
> Instead, use e.g. TFPCompactImgRGBA8Bit if you need alpha or
> TFPCompactImgRGB8Bit if you do not need Alpha.
>

Nice, I did not know we have more compact image types available. O.o

>>          dstImg:=TFPMemoryImage.Create(iX,iY);
>>          dstImg.UsePalette:=false;
>>          dstCanvas:=TFPImageCanvas.create(dstImg);
>>          dstCanvas.StretchDraw(0,0,iX,iY,srcImg);
>
> Phew, this is also a real killer.
>
> Do not draw on a canvas with stretchdraw. That will be slow as well;
> Rather, attempt to manipulate the image in memory by doing a stretch
> directly.
> Choose an algorithm which is fast. The default interpolation will result
> in quite a lot of calculations.

Maybe a collection of algorithms for in memory rescaling would be nice...

Regards,
Sven