Hi all,
I'm trying to draw some instanced geometry, passing a transform per
instance. I've set up a uniform array for each node I'm instancing,
which has a fixed number of values (I'm using 128 now) and that works well.
The problem is that this way of passing data seems limited to a small
number of matrices. As I said I'm using a size of 128, so 128*16 floats,
which doesn't seem like much (8192 bytes of memory). I want to increase
that (my initial goal was about 1024 instances). But if I increase this
just to 256, I get
Warning: detected OpenGL error 'invalid operation' after RenderBin::draw(,)
repeatedly on the console, and my instances don't display anything
(presumably the matrices it's getting are all zeros).
This is to be used to display small rocks as particles, so I really need
more than 128 of each rock type. One solution might be to increase the
number of rock types (so the number of drawables that will be
instanced), but I would prefer another way.
One thing I could see to increase the number of instances I can use is
to pass less data per instance, for example a vec3 translation, a float
uniform scale and a vec4 quaternion which gives 8 floats instead of 16
per instance. Would this work, i.e. am I right in my assumption that the
problem is the amount of data and not the number of elements in the array?
Another solution might be a texture. In a float texture, I could pass
(if I use the same members above, so 8 floats per instance) over 2
million instances in a 4096x4096 texture. So to get to my initial goal
of 1024 instances, I would need a 128x64 float texture, which seems
manageable, and I could potentially go much higher if I wanted to.
I've seen an example (osguniformbuffer) that used uniform buffer arrays,
I'm not sure if this would apply to what I'm doing but the usage seems
more complicated than a uniform mat4 array, so as long as the
performance difference isn't too large I'd prefer to use those.
Are there other ways to pass lots of data in an array to a vertex shader
that I haven't thought about? I've thought of the above options, so what
I'm asking is what other people have been using and what has worked for
them. Right now the float texture seems like the best option (especially
since the hardware we target seems fast at vertex texture fetch, which
we use for display of height fields).
Thanks in advance,
J-S
--
______________________________________________________
Jean-Sebastien Guay [email protected]
http://www.cm-labs.com/
http://whitestar02.webhop.org/
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