Board index » cppbuilder » Drawing on bitmap

2004-05-01 03:22:26 PM
cppbuilder3
It's required to draw pixels on TBitmap.
I've put TImage component on the Form, created Picture:
Image->Picture = new TPicture();
But after the operation
Image->Picture->Bitmap->Canvas->Pixels[x][y] = clRed;
form remains empty.
I know that I do this operation simply using
Image->Canvas->Pixels[x][y] = clRed;
Why? And how to do it correctly?
Thank you in advance.
 

XXXX@XXXXX.COM wrote:
Hans.
 

Hi,
automatically. If You create a new one, You might get trouble with
memory-leaks.
But it is neccessary, to set the bitmaps width and hight. Those are zero
in a new bitmap - So You are drawing far beyond the borders of the bitmap.
Image1->Picture->Bitmap->Width=whateveryouneed;
Image1->Picture->Bitmap->Height=whateveryouneed;
and it is also a good idea, to set the pixelformat according to Your
needs - Otherwise, the results may depend on the actual settings of the
computer:
Image1->Picture->Bitmap->PixelFormat=pf24Bit;
After this
By the way: Canvas->Pixels seems to be the slowest possible way to set a
pixel on the screen. If You want to change a lot of pixels have a look
at Bitmap->RowScan
Good Luck
Michael Kutscher
www.kutscher-software.de
 

{smallsort}

OK, it works now, thank you very much.
is to copy pixels from Bitmap1 (with pf32bit) to another one - Bitmap2
(also with pf32bit).
So, the previous code was as follows:
Graphics::TBitmap *Bitmap2;
Bitmap2 = new Graphics::TBitmap();
Bitmap2->PixelFormat = pf24bit;
Byte* ptr1, ptr2;
for (int y = 0; y < pBitmap1->Height; y++)
{
ptr2 = (Byte *)pBitmap2->ScanLine[y];
ptr1 = (Byte *)pBitmap1->ScanLine[y];
memcpy(ptr1, ptr2, pBitmap1->Width*4);
}
At the first string in cycle
ptr2 = (Byte *)pBitmap2->ScanLine[y];
at y = 0 the following error appears:
EInvalidGraphicOperation with message 'Scan line index out of range'.
Where is the problem here?
Probably, there is another way to copy one bitmap to another?
And how to modify this code if I want copy bits of pf32bit bitmap into
pf24bit bitmap?
Thanks in advance,
TM
 

Hi,
any way.
memcpy(ptr1, ptr2, pBitmap1->Width*3);
But, if You just want to copy pieces of a bitmap or a whole one, it
might be the better way, to simply draw or CopyRect it on the other one.
Thats less code and works fast as well.
copy the whole bitmap by drawing it an the other one:
Bitmap32->Canvas->Draw(0,0,Bitmap2);
I don't know, wether Convas->CopyRect would work correctly in this
situation, but I think it's worth a try. Modifying each pixel "manually"
doesn't look very effective...
Good luck
Michael Kutscher
 

Thank you very much for your help and explanations.