[Lazarus] Copy buffer of PWord to TMemoryStream

[Leonardo M. Ramé]

On 2013-03-24 20:02:38 +0100, Sven Barth wrote:
> On 24.03.2013 19:57, Leonardo M. Ramé wrote:
> >On 2013-03-24 19:46:09 +0100, Sven Barth wrote:
> >>On 24.03.2013 19:30, Leonardo M. Ramé wrote:
> >>>On 2013-03-24 19:21:49 +0100, Sven Barth wrote:
> >>>>On 24.03.2013 19:19, Joao Morais wrote:
> >>>>>2013/3/24 Leonardo M. Ramé <l.rame at griensu.com>:
> >>>>>>Hi, I'm copying a buffer of PWord to a TMemoryStream using this code:
> >>>>>>
> >>>>>>lTmpBuff := lBuffer;
> >>>>>>I := 0;
> >>>>>>while I < lBufSize do
> >>>>>>begin
> >>>>>>   lStream.Write(lTmpBuff^, SizeOf(PWord));
> >>>>>>   inc(lTmpBuff, 1);
> >>>>>>   inc(I, 1);
> >>>>>
> >>>>>What about:
> >>>>>
> >>>>>    inc(lTmpBuff, SizeOf(PWord));
> >>>>>    inc(I, SizeOf(PWord));
> >>>>
> >>>>If lTmpBuff is declared as PWord then "Inc" already increases in
> >>>>multiplies of "SizeOf(PWord)".
> >>>>Regarding lBufSize it will be important to know whether the C code
> >>>>returns the size in elements or in byte.
> >>>>
> >>>
> >>>Heres the interface of the library:
> [snip]
> >>Now if your C function is written correctly, all three should give
> >>you the same result.
> >>
> >
> >Thanks Sven, I modified the C function as this:
> >
> >bufSize = interdata->getCount(); // <- returns number of pixels
> >buffer = new Uint16[bufSize];
> >memcpy((void *)buffer, interdata->getData(), interdata->getCount());
> >
> >Here's the getCount() documentation:
> >http://support.dcmtk.org/docs/classDiPixel.html#15bbe5e57b15ea67bbc9541752ccccce
> >
> >Hence, my confusion is because I thought getCount was number of bytes,
> >but it is number of pixels :)
> >
> >After changing the C function, now I can do this:
> >
> >lStream.Write(lTmpBuff^, SizeOf(PWord));
> >inc(lTmpBuff);
> >inc(I, 2); // it also works with inc(I, 1) but not using inc(I,
> >sizeof(Word));
> >
> 
> Now your lBufSize contains the number of pixels, so only Inc(I, 1)
> should be correct. And for copying all data at once you now need to
> use "lBufSize * SizeOf(Word)" instead. And the for-loop variant
> would look like this:
> 
> === code begin ===
> 
> for i := 0 to lBufSize - 1 do
>   lStream.Write(lBuffer[i], SizeOf(Word));
>   // or
>   lStream.WriteWord(lBuffer[i]);
> 
> === code end ===
> 

Yes, the code looks correct, but it still creates the wrong resulting
image.

If you look at the attachment, the upper image is the result of your
last suggestion, while the lower image was created using the while loop
I've shown.

I'll re-check my drawing function, maybe your code is correct and the
problem is on that function.

-- 
Leonardo M. Ramé
http://leonardorame.blogspot.com
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