GL Point Structure Point Size

toneburst's picture

Now, this may be just user error on my part, but I'm getting a bit confused with point sizes when using the GL Tools Point Structure patch. It seems that when I switch my composition to fullscreen mode in the QC editor, all my points become much smaller. It also seems there's a maximum size beyond which they don't get any bigger, even if you set the Size parameter to a higher value.

Now, this may be something to do with the particular QTZ I'm working on. It's a variation on the 'Random Walk' experiments, and points can end up travelling quite a long way (in QC unit terms), in any direction, so maybe that's got something to do with it.

Also, is it normal for points to not get smaller with distance?

Any thoughts?

a|x

cwright's picture
Re: GL Point Structure Point Size

point size is in pixels, just as line width is in pixels. Thus, they'll stay the same size when going fullscreen, which will make them appear smaller. converting to QC units makes no sense because... -> (next section)

There's an upper limit on point size -- this is GPU/driver enfored, not a limitation imposed by us. There is no way to work around this (other than manually creating billboards instead of points, which quadruples the amount of data to shuffle along to the gpu and requires some matrix inversions)

points may or may not shrink based on size -- you need to enable "attenuation" on the patch, and have a gpu that honours point attenuation (Intel GPUs do not, I'm not sure if other gpus do or not -- apple's software renderer does).

usefuldesign.au's picture
Re: GL Point Structure Point Size

I've been using the attenuation on the Toneburst's "Random Walk" originated comp and they do vary in size on an Nvidia FX 5200. Although, I guess due to the GL Look At patch, the largest points are not necessarily at the front and smallest not at the at the back. The random layering is quite nice though.

toneburst's picture
Re: GL Point Structure Point Size

Glad it wasn't just me going mad, then...

cwright wrote:
point size is in pixels, just as line width is in pixels. Thus, they'll stay the same size when going fullscreen, which will make them appear smaller. converting to QC units makes no sense because... -> (next section)

Ah... makes sense. So I'd have to make them larger when the rendering destination increases in size.

Quote:
There's an upper limit on point size -- this is GPU/driver enfored, not a limitation imposed by us. There is no way to work around this (other than manually creating billboards instead of points, which quadruples the amount of data to shuffle along to the gpu and requires some matrix inversions)

I can see why that would be a bad idea. Unfortunately, I was making use of the fact that a point-sprite always remains screen-facing to avoid the points appearing distorted when the view changes. I'm not sure I could do the same thing with sprites. The maximum size seems to be about 70 pixels on my GPU, as far as I can tell, incidentally. I'd be interested to know what it is on other cards.

Quote:
points may or may not shrink based on size -- you need to enable "attenuation" on the patch, and have a gpu that honours point attenuation (Intel GPUs do not, I'm not sure if other gpus do or not -- apple's software renderer does).

They don't seem to on my MacBook Pro/X1600. Nothing changes if I check Attenuation.

a|x