[gameprogrammer] Re: OpenGL... Where are the calculations made?
- From: "Bob Pendleton" <bob@xxxxxxxxxxxxx>
- To: gameprogrammer@xxxxxxxxxxxxx
- Date: Wed, 7 May 2008 08:45:53 -0500
On Wed, May 7, 2008 at 2:32 AM, richard sabbarton <
richard.sabbarton@xxxxxxxxx> wrote:
> Hi Guys,
>
> I have another question regarding OpenGL and I am hoping you can clear
> something up for me. If I run matrix manipulation functions using
> OpenGL (e.g. glTranslate(), glRotate(), gluLookAt(), etc.) I am
> assuming that the calculations required to perform these functions are
> performed by the GPU on the Graphics adapter rather than the CPU. Is
> this correct? Does that mean that the glMatrix is stored in the
> memory of the graphics adapter or in my system RAM? I am asking
> because I assume that the GPU can process these calculations quicker
> and more efficiently than the CPU can.
It is implementation dependent, but for any modern graphics add
>
>
> For example, if I want to calculate a cross-product or face normal I
> can use sin(), cos(), etc to perform the calculations but, IMO, these
> can be quite costly as far as CPU time. So what if, instead of using
> sin() & cos() I was to use glXxxx functions instead. I could load an
> identity matrix and then use gluLookAt() to look at point A and supply
> point B as an Up Vector. I can then translate 1.0 along the X axis
> and pluck my normalised cross-product from the matrix. No sin(),
> cos() or sqrt() in sight. Do you think this will be quicker? Also, I
> am not sure about the overhead of pulling the values from the Matrix
> as (another assumtion) would this involve copying the matrix from the
> Graphics Memory into the System Memory?
Do not do that. The cost of moving the data back and forth from system
memory and the GPU is very high and is much more costly than just doing the
computation you want in the CPU. If the math your are doing is slowing you
project down, then you should first see if the math can be done faster in
the CPU. You can often skip many steps in your math and speed it up a lot.
In some cases you can't and then you might want to look at shader
programming to solve your problem.
Here is a suggestion: instead of asking if and idea is a good idea for
solving a low level problem, step back a bit and ask us how to solve your
high level problem. We can be a lot more helpful when we know what you are
trying to do rather than just who you are trying to do it.
Bob Pendleton
>
>
> Regards
>
> Richard
>
> ---------------------
> To unsubscribe go to http://gameprogrammer.com/mailinglist.html
>
>
>
--
+ Bob Pendleton: writer and programmer
+ email: Bob@xxxxxxxxxxxxx
+ web: www.GameProgrammer.com
+ www.Wise2Food.com
+--------------------------------------+
Other related posts:
