[PD] How do I squeeze more performance out of Gem?

Thu Mar 10 06:20:47 CET 2011

Ok so I did something stupid with the
[GEMglLightModeliGL_LIGHT_MODEL_TWO_SIDE GL_FALSE] test which that I
connected it to a
[gemhead] instead of [gemhead 1]. When I corrected that I did find that
indeed the performance changes drastically for the better. OTOH I couldn't
get satisfactory lighting for my environment. It's a good technique for me
to remember and I could probably make it work even for this project with
enough experimentation of lighting sources and direction but...

it seems clear to me on my system at least with GL_LIGHT_MODEL_TWO_SIDE set
to its default GL_TRUE the bottleneck is the lighting and any gains with a
display list or model are lost because of the lighting issue. However I'm
finding that I get satisfactory performance and appearance by changing the
sphere to have 10 segments instead of 30. With a 10 segment sphere I can
make 1000 spheres and straight-line curves at 20fps at about 70% draw on a
CPU core. That works for me! :-)

I was curious if for a future project there might be a way I could make a
shader that would emulate the local lighting effect and do it more
efficiently. Serious exploration with shaders definitely needs to be in my
future.

In any case, thanks for all the help!

-John

On Wed, Mar 9, 2011 at 1:55 PM, cyrille henry <ch at chnry.net> wrote:

> with lighting on, things did not really change with the model or display
> list, but rendering sphere is 2 time slower.
>
> here is the sphere.
>
> Cyrille
>
> Le 09/03/2011 20:44, John Harrison a écrit :
>
>> It appears I'm actually getting better results from [gemlist] too with
>> lighting off. But how do your results change with lighting on? For me, with
>> lighting on, they seem about the same.
>>
>> If you have your sphere.obj model with 900 triangles handy, I'd love to
>> try it.
>>
>> -John
>>
>> On Wed, Mar 9, 2011 at 12:19 PM, cyrille henry <ch at chnry.net <mailto:
>> ch at chnry.net>> wrote:
>>
>>    here, at 20fps, no lighting, i can draw about 500 model with your
>> sphere.obj.
>>    1000 sphere 30, and about 3500 display list of sphere 30.
>>    using an other sphere.obj with about 900 triangles, i've got the same
>> performance than with the display list.
>>
>>    it really is strange that the sphere is the fastest on your computer.
>>
>>    Cyrille
>>
>>
>>    Le 09/03/2011 19:08, John Harrison a écrit :
>>
>>        Using Cyrille's test patch for speed which he sent into the list a
>> week or so ago, I tried creating multiple spheres, gemlists, and models. The
>> sphere is getting the best performance results, unfortunately. Attached is
>> my test patch. I just connected [repeat] to either [sphere] [GEMglCallList]
>> or [model] in the patch. The sphere model I used has probably got way too
>> many points (just found it on the 'net) but my hope was that as the vertices
>> were static it wouldn't matter.
>>
>>        http://www.eecs.umich.edu/~guskov/eecs598-1/sphere.obj <
>> http://www.eecs.umich.edu/%7Eguskov/eecs598-1/sphere.obj>
>>
>>
>>        maybe one with less vertices will help. I can try...
>>
>>        -John
>>
>>        On Wed, Mar 9, 2011 at 9:48 AM, chris clepper <cgclepper at gmail.com<mailto:
>> cgclepper at gmail.com> <mailto:cgclepper at gmail.com <mailto:
>> cgclepper at gmail.com>>> wrote:
>>
>>            A model is the way to go since the vertex data is static.
>>  Ideally for situations like this there would be one object that loads a
>> single model and several clients that just call the display list.  Although
>> there is a lot of memory on GPUs now so 200 models of a sphere won't take up
>> that much.
>>
>>            On Wed, Mar 9, 2011 at 10:32 AM, John Harrison <
>> johnharrisonwsu at gmail.com <mailto:johnharrisonwsu at gmail.com> <mailto:
>> johnharrisonwsu at gmail.com <mailto:johnharrisonwsu at gmail.com>>> wrote:
>>
>>
>>
>>
>>
>>                        On Wed, Mar 9, 2011 at 1:59 AM, cyrille henry <
>> ch at chnry.net <mailto:ch at chnry.net> <mailto:ch at chnry.net <mailto:
>> ch at chnry.net>> <mailto:ch at chnry.net <mailto:ch at chnry.net> <mailto:
>> ch at chnry.net <mailto:ch at chnry.net>>>> wrote:
>>
>>                            hello,
>>
>>                            - try using a display list to render a sphere,
>> so that every point don't have to be send for every sphere.
>>                            see exemple 09.openGL/02.displaylist
>>                            you can also use a model with a sphere.obj to
>> have the same result.
>>
>>                        if the spheres are all moving at once, would a
>> display list still help? Seems like recompilation would have to happen for
>> every sphere for every frame? I haven't tried the model yet...
>>
>>                    yes, the display list will help to render 1 single
>> sphere.
>>                    you have to call it 200 times.
>>
>>
>>                Ok I'm seeing a huge performance difference between using
>> 200 of [sphere <size-doesn't-matter> 20] and [sphere <size-doesn't-matter>
>> 30]. Huge. So if I want to keep the sphere with 30 points, I'm thinking
>> gemlist or model are my answer. I'll try both and report back, unless you
>> have a strong recommendation for one or the other to save me time.
>>
>>                This list is awesome. Where else could I find help like
>> this? :-)
>>
>>                -John
>>
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-- 
John
http://alumni.media.mit.edu/~harrison/
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