[Lazarus] Copy buffer of PWord to TMemoryStream

[Leonardo M. Ramé]

On 2013-03-24 20:44:50 +0100, Sven Barth wrote:
> On 24.03.2013 20:39, Leonardo M. Ramé wrote:
> >>>>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.
> >>
> >>I just noticed that you are still using "SizeOf(PWord)" in your
> >>lStream.Write. This is wrong. You want to copy one Word element
> >>(SizeOf(Word)=2) instead of two/four (depending on 32 vs 64 bit
> >>SizeOf(PWord) is either 4 or 8). Which is also why your Inc(..., 2)
> >>works as you are copying multiple entries at once.
> >>
> >
> >Well, this is funny, after re-checking the code, I noted it works if I
> >use this:
> >
> >(1)   for I := 0 to lBufSize - 1 do
> >         lUnCompressed.Write(lTmpBuff[i], SizeOf(PWord));
> >
> >But, using SizeOf(Word) doesn't:
> >
> >(2)   for I := 0 to lBufSize - 1 do
> >         lUnCompressed.Write(lTmpBuff[i], SizeOf(Word));
> >
> >What I would like to achieve is this:
> >
> >(3)   lUnCompressed.WriteBuffer(lTmpBuff^, lBufSize * SizeOf(Word));
> >
> >But using this, I get the same result of (2).
> >
> 
> Maybe your problem is indeed in your drawing function. Because the
> usage of SizeOf(PWord) is definitely wrong if your lBuffer basically
> contains Word sized pixels after each other. You should currently
> even get different results depending on whether the application is
> 32 or 64 bit.
> 
> Regards,
> Sven
> 

Sven, I can confirm the image display function was wrong. Now I can
write all data to the stream at once!.

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