Independent Glow for DE objects with Ray Marching ?

[glennmarshall]

Hi
I'm just wondering if it's possible to put glow on individual parts / objects within a DE scene using Ray Marching - e.g. having lots of spheres with a glow around them, but not the other objects in the scene.

And to expand further - would it be possible to add basic transparency / luminance to objects individually..
Basically I'd love to have my Ray Marcher do most of the things a standard 3d Ray Tracer could do.

I'm using this code for my work,
http://www.openprocessing.org/sketch/73427

Thanks..

[glennmarshall]

i'm nearly there with the glow idea at least,
in this scene - I created a scaled up DE of the red sphere - and used it's value as a multiplier for the red glow - so that the entire scene doesn't get the glow, just the area around the red sphere.

the little problem i'm still having is that the glow is creating a strange banding artifiact on the background sky - looking into that now.
http://imgur.com/v03VcMd

[cKleinhuis]

thank you for sharing, yet nice results, it all comes down to your object definition
BUT, you are tricking around, the glow should be - in my eyes - implemented as some kind of volumetric stuff, and the DE value should give you a densitiy value, similar to how cloud rendering using a raymarcher would work, problem with cloud rendering is that every point in a volumetric object emits light but in ALL directions

[glennmarshall]

oh it's a shameless hack of someone else's code I'll admit, I'm far from an expert 3d programmer..

[glennmarshall]

although it only adds the glow to geometry close to it so it seems- not background stuff in the distance - as seen in this version with a stronger glow..

[elphinstone]

It's a technique I still not tried, but I think it's a good starting point for adding volumetric glow outside the sphere:

• add a sphere concentric to the one you want to add glow to
• when a ray intersects it check both intersections and measure the distance between them
• scale the glow color using the distance calculate.
• Let the ray continue through the scene (the glow sphere should not block it) and sum the traced color to the scaled glow color.

For scaling the glow color make a distinction of the two cases:

• The ray intersects only the glow sphere: then
• The ray intersects both spheres: the math gets a bit compicated here.. as a decent approximation I suggest to use just . Or maybe you can get interesting results using no glow in this case.

Where and are the radius of the sphere and of the glow sphere. is the measured distance, the scale factor.

Hope it helps This works just for spheres, but the idea is to use a scaled version of the shape you are drawing as "glow shape". The most accurate approach would be to "grow" the shape along the normals, but I think it gets really complicated :S

[glennmarshall]

Thanks - I think I get the gist of what you're saying - I might attempt it soon - for now I'd be happy with a quick hack.  If can get rid of the banding effect on the background sky I'd be happy - picture attached.  The glow seems to be horizontally applied to the sky - I'm trying to exclude the sky from all glow effects..

[Syntopia]

You can also just keep track of the closest distance to the objects you want to glow. And then add some color based on this distance in your lighting code:

[glennmarshall]

thanks Syntopia! I think I could get my head around that - I'll give it a try and get back with any results / questions

[glennmarshall]

I actually decided to pursue the method I had started - and got it working the way I wanted.  I figured out the 'real' glow method - but what I was doing seemed more interesting, it's more of an intense radiosity / bounce effect.  I think it will lend itself to interesting colors and textures when working with something more complicated like an iterative fractal.  Thanks for all the help anyway - I'll post more pics as I develop the idea more.