dotnet drawing api: Lockbits question -- dotnet drawing api

You're in the

dotnet drawing api

group:

Lockbits question

Lockbits question

keperry
10/26/2006 2:43:25 PM

dotnet drawing api:

Ok..so I was trying to follow the example on Bob's site:
(http://www.bobpowell.net/lockingbits.htm)

BitmapData bmd=bm.LockBits(new Rectangle(0, 0, 10, 10),
System.Drawing.Imaging.ImageLockMode.ReadOnly, bm.PixelFormat);

int PixelSize=4;

for(int y=0; y<bmd.Height; y++)

{

byte* row=(byte *)bmd.Scan0+(y*bmd.Stride);

for(int x=0; x<bmd.Width; x++)

{

row[x*PixelSize]=255;

}

}

Supposedly, the "row[x*PixelSize] = 255" can be used to access the blue
byte. Can someone give an example of how I can access the red, green,
and alpha bytes? Assuming its a Format32BppArgb?

Re: Lockbits question

keperry
10/26/2006 6:12:43 PM

Dang...that's what I thought. I keep getting an error towards the end
saying that I tried to write or read protected memory. So I thought
maybe I was going out of bounds or something.

Re: Lockbits question

keperry
10/26/2006 7:05:20 PM

Thanks for the reply btw!

When I setup my bitmap, I was setting the format to 32bit, but when I
specified my BitmapData I set it up as a 24 bit. That's why I was
running out of memory.

Re: Lockbits question

keperry
10/26/2006 7:09:53 PM

Thanks for the reply! I like your way, too.

[quoted text, click to view]

Re: Lockbits question

Joergen Bech <jbech<NOSPAM> NO[at]SPAM
10/27/2006 12:37:40 AM

Little-Endian order?

index + 0 = blue
index + 1 = green
index + 2 = red
index + 3 = alpha

e.g. row(x*PixelSize + 2)=<red value>

/JB

On 26 Oct 2006 14:43:25 -0700, "keperry" <keith.b.perry@gmail.com>
[quoted text, click to view]

Re: Lockbits question

Michael C
10/27/2006 12:00:10 PM

[quoted text, click to view]

I usually do this slightly differently

BitmapData bmd=bm.LockBits(new Rectangle(0, 0, 10, 10),
System.Drawing.Imaging.ImageLockMode.ReadOnly, bm.PixelFormat);

int PixelSize=4;
byte* ptr = (byte*)bmd.Scan0;
int offset = bmd.stride - PixelSize * bmd.Width;

for(int y=0; y<bmd.Height; y++, ptr += offset)

{

for(int x=0; x<bmd.Width; x++, ptr += PixelSize)

{

ptr[RGB.A] = whatever;
ptr[RGB.R] = whatever;
ptr[RGB.G] = whatever;
ptr[RGB.B] = whatever;

}

}

where RGB.A, R, G and B are constants in a class called RGB.
public const int A = 3;

public const int R = 2;

public const int G = 1;

public const int B = 0;

[quoted text, click to view]

Got something to say? Click here to post a reply to this thread.

Don't see what you're looking for? Try a search.

View other messages in the dotnet drawing api group.

View Other Months
June 2003
July 2003
August 2003
September 2003
October 2003
November 2003
December 2003
January 2004
February 2004
March 2004
April 2004
May 2004
June 2004
July 2004
August 2004
September 2004
October 2004
November 2004
December 2004
January 2005
February 2005
March 2005
April 2005
May 2005
June 2005
July 2005
August 2005
September 2005
October 2005
November 2005
December 2005
January 2006
February 2006
March 2006
April 2006
May 2006
June 2006
July 2006
August 2006
September 2006
October 2006
November 2006
December 2006
January 2007
February 2007
March 2007
April 2007
May 2007
June 2007
July 2007
August 2007
September 2007
October 2007
November 2007
December 2007
January 2008
February 2008
March 2008
April 2008
May 2008
June 2008

home · blog · groups

Questions? Comments? Contact the dn