Why myBitmap-GetPixel() crashes sometimes?

[manu.20]

Dear *;

I have a difficult problem:

I tried to use the methode:
GetPixel(), but it crashs, when I use it, here my is code:

In the header-file:
CFbsBitmap* myBitmap;

I load my image fro the mbm-file:
myBitmap = NBitmapMethods::CreateBitmapL(KMBMFileName,EMbmBildBmp1);

using the class bitmapmethods (Is there an other possibility?)

and the I try a loop, that gives me the color of the pixel:

TInt iX = 0,iY = 0;
TRgb* aColor;
TSize BmpSize = myBitmap->SizeInPixels();

for (iY = 0; iY < BmpSize.iHeight; iY++) {
for (iX = 0; iX < BmpSize.iWidth; iX++) { myBitmap->GetPixel(*aColor, TPoint(iY,iX));
}
}

But it crashs in the emulator on the GetPixel()-position

Does anybody know why?

Thank you very much
Manu

[greatape]

Originally posted by manu.20
...TPoint(iY,iX));...

Because you've put iY & iX the wrong way round.

[manu.20]

Thank you very much for your help greatape!

But I think this is not the problem, because it crashes in the first loop and there iX and iY are 0. It even crashs, when I write:
MyBitmap->GetPixel(*aColor, TPoint(5,5));

The error is an untreated exception in epoc.exe (FBSCLI.DLL).

Can plz tell me anybody, why?

[chrishawaii]

Hi Manu,
I really enjoy to answer your postings...
There's only one line missing in your code:

TBitmapUtil bitmapUtil(yourBitmap);

Yeah!
So you have an handle on your bitmap (previous to your loop). Even if you don't use the methods of this handle, you have to take it.
But maybe we can talk about it by lunch?

Best regards
Christian

[Marat Khalili]

I cannot have lunch with you guys, but can you please say a few words in what situations taking handle is necessary? This is very interesting, I didn't care to do it so far, but my bitmap operations are very limited.

[chrishawaii]

Hi Marat,
when you want to handle a bitmap it's important to have this handle on the bitmap. Without it you have no access (fortunately).
Christian

[Marat Khalili]

Thank you chrishawaii, but what exactly do you mean by "handling" the bitmap? I was able to draw on the bitmap, draw the bitmap, use methods like ScanLineLength, GetScanLine, SetScanLine of the bitmap, and even feed bitmaps to CImageDecoder without getting any handles, although I've heard with handles something might be faster. I didn't try to get separate pixels though.

What devices require getting a handle? I'm using Series 60 Nokias like 6600 and 6630.

[chrishawaii]

She (Manu) tried to use the GetPixel method without having a TBitmapUtil bitmapUtil(CameraBitmap); on her bitmap.
That doesn't work.
You better asked me, why the GetPixel()-method of the class TBitmapUtil doesn't give the right pixel-value, although all other methods work fine. Otherwise this class would be very convenient to use.
I don't know.

[Marat Khalili]

Ok, I understood that I should not worry about my methods, thank you. BTW who needs GetPixel anyway, I expect it to be orders slower than GetScanLine.

[robota softwarehouse]

You are passing a reference to undefined (unallocated TRgb).

Maybe you try changing:

TRgb* aColor;

and GetPixel(*aColor ..

to

TRgb aColor;
GetPixel(aColor, ...

Good luck,

-arne

[chrishawaii]

hi arne,
why do you prefer this way? what is the advantage in disclaiming pointer?
did you try this way? did you disclaim the handle on the bitmap:
TBitmapUtil bitmapUtil(yourBitmap); ???
That would be interesting. does your way really work?

chris