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Author Topic: Independent Glow for DE objects with Ray Marching ?  (Read 2127 times)
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glennmarshall
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« on: June 12, 2013, 09:26:34 AM »

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..
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glennmarshall
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« Reply #1 on: June 12, 2013, 01:37:31 PM »

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


* glow.png (136.85 KB, 661x427 - viewed 301 times.)
« Last Edit: June 12, 2013, 01:42:42 PM by glennmarshall » Logged
cKleinhuis
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« Reply #2 on: June 12, 2013, 01:45:23 PM »

thank you for sharing, yet nice results, it all comes down to your object definition wink
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 wink
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glennmarshall
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Posts: 26


« Reply #3 on: June 12, 2013, 01:57:06 PM »

oh it's a shameless hack of someone else's code I'll admit, I'm far from an expert 3d programmer..
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glennmarshall
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« Reply #4 on: June 12, 2013, 02:01:53 PM »

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..


* glow2.png (130.65 KB, 681x394 - viewed 274 times.)
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elphinstone
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mattia.gollub
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« Reply #5 on: June 12, 2013, 02:40:52 PM »

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 s=\frac{d}{2*\sqrt(r_g^2-r_s^2)}
  • The ray intersects both spheres: the math gets a bit compicated here.. as a decent approximation I suggest to use just s=1. Or maybe you can get interesting results using no glow in this case.
Where r_s and r_g are the radius of the sphere and of the glow sphere. d is the measured distance, s the scale factor.

Hope it helps smiley 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
« Last Edit: June 12, 2013, 05:57:40 PM by elphinstone » Logged
glennmarshall
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« Reply #6 on: June 12, 2013, 05:50:23 PM »

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..


* glow3.png (165.12 KB, 711x461 - viewed 292 times.)
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Syntopia
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« Reply #7 on: June 12, 2013, 11:09:55 PM »

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:

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glennmarshall
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« Reply #8 on: June 13, 2013, 12:20:39 AM »

thanks Syntopia! I think I could get my head around that - I'll give it a try and get back with any results / questions smiley
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glennmarshall
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Posts: 26


« Reply #9 on: June 13, 2013, 09:23:23 PM »

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.


* glow4.png (175.63 KB, 727x447 - viewed 307 times.)
« Last Edit: June 14, 2013, 01:34:53 PM by glennmarshall » Logged
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