[Lazarus] Copy buffer of PWord to TMemoryStream

[Sven Barth]

On 24.03.2013 21:09, Leonardo M. Ramé wrote:
> 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!.
>

Nice to hear that you found the final problem as well :)

Regards,
Sven