Blitting

[Jon Slaughter]

Is it faster to modify array of ints as 32-bit pixel data and then somehow
turn that into a bitmap or use lockbits? I'm having a little performance
issues with lock bits unfortunately. I figure that I shouldn't have any
issues writing to an array and then maybe there is a faster way to convert
that into a bitmap than using lockbits?


Thanks,
Jon

[Bob Powell [MVP]]

Re: Blitting

Hi John,
What performance issues are you having with LockBits? If you're programming
C# then you should surely be using unsafe code and not the Marshal class for
access.

--
--
Bob Powell [MVP]
Visual C#, System.Drawing

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"Jon Slaughter" <Jon_Slaughter@ Hotmail.comwrot e in message
news:gCfFi.3328 1$RX.32818@news svr11.news.prod igy.net...

Is it faster to modify array of ints as 32-bit pixel data and then somehow
turn that into a bitmap or use lockbits? I'm having a little performance
issues with lock bits unfortunately. I figure that I shouldn't have any
issues writing to an array and then maybe there is a faster way to convert
that into a bitmap than using lockbits?
>
>
Thanks,
Jon
>

[Jon Slaughter]

Re: Blitting


"Bob Powell [MVP]" <bob@spamkiller bobpowell.netwr ote in message
news:CEBF3DAE-0D4D-44C5-B6AD-A12262DF3287@mi crosoft.com...

Hi John,
What performance issues are you having with LockBits? If you're
programming C# then you should surely be using unsafe code and not the
Marshal class for access.
>

Did you look at my code? I'm not sure what you mean by unsafe and
marshaling? I used unsafe to access the lockbits... its all in the code I
pasted...

crap... lol, I guess I didn't paste any code ;/

Ok, here it is... Its kinda messy but shows what I'm doing when using
lockbits(I pretty much copied and pasted from some other site that said to
use this method.

When I run this under VS I get about 1fps. When I run it outside of VS I get
about 10-20fps or so. (it might actually be fast but its slightly jerky)


Thanks,
Jon

bmd = bitmap.LockBits (R, System.Drawing. Imaging.ImageLo ckMode.ReadOnly ,
bitmap.PixelFor mat);

unsafe

{

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

{

byte* row = (byte*)bmd.Scan 0 + (y * bmd.Stride);

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

{

c = (int)(t) % 255;



row[x * PixelSize + 2] = (byte)(255*(Mat h.Pow((c/255F),0.8)));

row[x * PixelSize + 1] = (byte)(255*(Mat h.Pow((c/255F),2)));

row[x * PixelSize + 0] = (byte)(255*(Mat h.Pow((c/255F),3)));

}

}

} // unsafe

bitmap.UnlockBi ts(bmd);



BitmapGraphics2 .DrawImage(bitm ap, 0, 0);

[Ben Voigt [C++ MVP]]

Re: Blitting


"Jon Slaughter" <Jon_Slaughter@ Hotmail.comwrot e in message
news:AmkFi.6727 $JD.2899@newssv r21.news.prodig y.net...

>
"Bob Powell [MVP]" <bob@spamkiller bobpowell.netwr ote in message
news:CEBF3DAE-0D4D-44C5-B6AD-A12262DF3287@mi crosoft.com...

>Hi John,
>What performance issues are you having with LockBits? If you're
>programming C# then you should surely be using unsafe code and not the
>Marshal class for access.
>>

>
>
Did you look at my code? I'm not sure what you mean by unsafe and
marshaling? I used unsafe to access the lockbits... its all in the code I
pasted...
>
crap... lol, I guess I didn't paste any code ;/
>
Ok, here it is... Its kinda messy but shows what I'm doing when using
lockbits(I pretty much copied and pasted from some other site that said to
use this method.
>
When I run this under VS I get about 1fps. When I run it outside of VS I
get about 10-20fps or so. (it might actually be fast but its slightly
jerky)
>
>
Thanks,
Jon
>
bmd = bitmap.LockBits (R, System.Drawing. Imaging.ImageLo ckMode.ReadOnly ,
bitmap.PixelFor mat);

ReadOnly doesn't look right for this.

>
unsafe
>
{
>
for (int y = 0; y < bmd.Height; y++)
>
{
>
byte* row = (byte*)bmd.Scan 0 + (y * bmd.Stride);
>
for (int x = 0; x < bmd.Width; x++)
>
{
>
c = (int)(t) % 255;
>
>
>
row[x * PixelSize + 2] = (byte)(255*(Mat h.Pow((c/255F),0.8)));
>
row[x * PixelSize + 1] = (byte)(255*(Mat h.Pow((c/255F),2)));
>
row[x * PixelSize + 0] = (byte)(255*(Mat h.Pow((c/255F),3)));
>
}
>
}
>
} // unsafe
>
bitmap.UnlockBi ts(bmd);
>
>
>
BitmapGraphics2 .DrawImage(bitm ap, 0, 0);
>
>

Which part is the slowdown (use Diagnostics.Sto pwatch)? The LockBits,
filling in the array, UnlockBits, or DrawImage?

I doubt the computations are the bottleneck, but you can surely remove some
redundant code there, use repeated addition to find row instead of
multiplying by y, precompute x*PixelSize, and (c / 255). Also multiplying
will be much faster than Math.Pow for the integral cases.

If I'm right and the for loops are fast enough, then you can surely get a
very good frame rate (i.e. hit monitor's refresh rate with plenty of cycles
to spare) using OpenGL with glDrawPixels. A little more work for you, but
you'll get direct transfers to video memory and thence to the screen. If
you move up to a texture with glTexImage2D, a lot of effects become
essentially free at that point as well (transparency for watermarking or
fading in and out, rotation, stretching, etc).

[Doug Semler]

Re: Blitting

"Jon Slaughter" <Jon_Slaughter@ Hotmail.comwrot e in message
news:AmkFi.6727 $JD.2899@newssv r21.news.prodig y.net...

>
"Bob Powell [MVP]" <bob@spamkiller bobpowell.netwr ote in message
news:CEBF3DAE-0D4D-44C5-B6AD-A12262DF3287@mi crosoft.com...

>Hi John,

>
bmd = bitmap.LockBits (R, System.Drawing. Imaging.ImageLo ckMode.ReadOnly ,
bitmap.PixelFor mat);

ReadOnly works for you here? I've always gotten "attempt to write to
protected memory" exceptions whenever I tried to write to memory I've
obtained via a readonly lockbits <g>

What is the original bitmap's depth/pixel format? If I rember correctly, i
have had performance problems in the past with LockBits when using palette
(8bpp grayscale) bitmaps created from jpegs.

--
Doug Semler, MCPD
a.a. #705, BAAWA. EAC Guardian of the Horn of the IPU (pbuhh).
The answer is 42; DNRC o-
Gur Hfrarg unf orpbzr fb shyy bs penc gurfr qnlf, abbar rira
erpbtavmrf fvzcyr guvatf yvxr ebg13 nalzber. Fnq, vfa'g vg?

[Jon Slaughter]

Re: Blitting


"Doug Semler" <dougsemler@gma il.comwrote in message
news:em3Xn8C9HH A.5404@TK2MSFTN GP02.phx.gbl...

"Jon Slaughter" <Jon_Slaughter@ Hotmail.comwrot e in message
news:AmkFi.6727 $JD.2899@newssv r21.news.prodig y.net...

>>
>"Bob Powell [MVP]" <bob@spamkiller bobpowell.netwr ote in message
>news:CEBF3DA E-0D4D-44C5-B6AD-A12262DF3287@mi crosoft.com...

>>Hi John,

>>
>bmd = bitmap.LockBits (R, System.Drawing. Imaging.ImageLo ckMode.ReadOnly ,
>bitmap.PixelFo rmat);

>
ReadOnly works for you here? I've always gotten "attempt to write to
protected memory" exceptions whenever I tried to write to memory I've
obtained via a readonly lockbits <g>
>

I write ReadWrite and others and all the same result. The page I got this
code from had ReadOnly so I kepted it. Since I don't really know what it
does I kepted it like that. (even though one would expect that it would
prevent writing to the bits).

What is the original bitmap's depth/pixel format? If I rember correctly,
i have had performance problems in the past with LockBits when using
palette (8bpp grayscale) bitmaps created from jpegs.
>

32bit. ARGB. I guess atleast. I'm just creating a standard bitmap which I
suppose uses the display device parameters. Didn't really bother with
checking since I figure if it was something strange then it wouldn't look
right. (if it was 16 bits then and I treated it was 32bit then I wouldn't
get the correct picture).

[Jon Slaughter]

Re: Blitting


"Ben Voigt [C++ MVP]" <rbv@nospam.nos pamwrote in message
news:OnLDzxA9HH A.5316@TK2MSFTN GP04.phx.gbl...

>
"Jon Slaughter" <Jon_Slaughter@ Hotmail.comwrot e in message
news:AmkFi.6727 $JD.2899@newssv r21.news.prodig y.net...

>>
>"Bob Powell [MVP]" <bob@spamkiller bobpowell.netwr ote in message
>news:CEBF3DA E-0D4D-44C5-B6AD-A12262DF3287@mi crosoft.com...

>>Hi John,
>>What performance issues are you having with LockBits? If you're
>>programming C# then you should surely be using unsafe code and not the
>>Marshal class for access.
>>>

>>
>>
>Did you look at my code? I'm not sure what you mean by unsafe and
>marshaling? I used unsafe to access the lockbits... its all in the code I
>pasted...
>>
>crap... lol, I guess I didn't paste any code ;/
>>
>Ok, here it is... Its kinda messy but shows what I'm doing when using
>lockbits(I pretty much copied and pasted from some other site that said
>to use this method.
>>
>When I run this under VS I get about 1fps. When I run it outside of VS I
>get about 10-20fps or so. (it might actually be fast but its slightly
>jerky)
>>
>>
>Thanks,
>Jon
>>
>bmd = bitmap.LockBits (R, System.Drawing. Imaging.ImageLo ckMode.ReadOnly ,
>bitmap.PixelFo rmat);

>
ReadOnly doesn't look right for this.
>

>>
>unsafe
>>
>{
>>
>for (int y = 0; y < bmd.Height; y++)
>>
>{
>>
>byte* row = (byte*)bmd.Scan 0 + (y * bmd.Stride);
>>
>for (int x = 0; x < bmd.Width; x++)
>>
>{
>>
>c = (int)(t) % 255;
>>
>>
>>
>row[x * PixelSize + 2] = (byte)(255*(Mat h.Pow((c/255F),0.8)));
>>
>row[x * PixelSize + 1] = (byte)(255*(Mat h.Pow((c/255F),2)));
>>
>row[x * PixelSize + 0] = (byte)(255*(Mat h.Pow((c/255F),3)));
>>
>}
>>
>}
>>
>} // unsafe
>>
>bitmap.UnlockB its(bmd);
>>
>>
>>
>BitmapGraphics 2.DrawImage(bit map, 0, 0);
>>
>>

>
Which part is the slowdown (use Diagnostics.Sto pwatch)? The LockBits,
filling in the array, UnlockBits, or DrawImage?
>
I doubt the computations are the bottleneck, but you can surely remove
some redundant code there, use repeated addition to find row instead of
multiplying by y, precompute x*PixelSize, and (c / 255). Also multiplying
will be much faster than Math.Pow for the integral cases.
>
If I'm right and the for loops are fast enough, then you can surely get a
very good frame rate (i.e. hit monitor's refresh rate with plenty of
cycles to spare) using OpenGL with glDrawPixels. A little more work for
you, but you'll get direct transfers to video memory and thence to the
screen. If you move up to a texture with glTexImage2D, a lot of effects
become essentially free at that point as well (transparency for
watermarking or fading in and out, rotation, stretching, etc).

Yes, I should be able to get it a good frame rate. I just need to work at
the pixel level because I am trying to do a physics simulation. The display
is only to display the result of the simulation periodically. I have some
other simulations that I've done but I didn't use lock bits and they seem
pretty fast. This is first time I'm using lock bits but potentially code is
slow when I'm actually doing the simulation(but shouldn't be that slow).

What I did notice is that when I run it under VS its about 20 times slower
even if in active mode. So the debugger is making it very slow and I
probably got confused when I was running it and with the simulation.

Essentially I'm calculating two gaussians and maybe the math library is
pretty slow. I guess I'll need to precalculate the guassians and see how
that works. I'll try to profile it sometime but distracted writing a vector
library ATM.

Thanks,
Jon