Ideas for creating gradual burning grass?

[CatTaker]

Hey,

I have a thinking problem about how to get started in creating gradual burning grass. I have that idea in my head about making some sort of edge ring where it's gradualy getting bigger to the point where it explodes. My main problem (besides other problems  im new to houdini and this whole VFX) is how to make grass start burning while edge ring of that circle is getting bigger? I have pretty good undarstanding of basics in Houdini but is that to much for me to be able to handle this? Im not in hurry, it's personal project for me. Making grass should be straighforward but how to make it burn realistycally? 

[vtrvtr]

Well, it depends on a lot of things. Mainly on how far is the camera. Because the difference between doing it with shaders in a general sense and doing it to each "grass" is enormous here. The former is relatively easy, the latter would take some fiddling 

For doing it with shaders, that is, it would be a camera very far from the grass, you can simply use some kind of noise and/or geometry to transfer an attribute that will drive the shader from "healthy" to "burned" 

Then you can use the same idea to drive any simulation (e.g fire and smoke) to complement it

Take a look

 

grass_odf.hip

[CatTaker]

52 minutes ago, vtrvtr said:

Well, it depends on a lot of things. Mainly on how far is the camera. Because the difference between doing it with shaders in a general sense and doing it to each "grass" is enormous here. The former is relatively easy, the latter would take some fiddling 

For doing it with shaders, that is, it would be a camera very far from the grass, you can simply use some kind of noise and/or geometry to transfer an attribute that will drive the shader from "healthy" to "burned" 

Then you can use the same idea to drive any simulation (e.g fire and smoke) to complement it

Take a look

 

grass_odf.hip

Yeah totaly forgot about some details. Im gona use real footage where i will do camera tracking, HDR ( in case i will need it), and some measurements. Object will be about 50 m from the camera and the ring will be growing from this object up to 30 m. So the closest part of the burning grass will be 20 m. On the edge of the ring there will be a fire (imagine it as a fire ring). Inside a circle there will be a symbol - pentagram with will be also in fire. The symbol will scale proportianolly to the size of the edge circle starting from the beggining of the simulation. Fire of this symbol will be different, less noisy, more calm then the fire on the edge of the circle. It doesnt have to be super realistic but i want to convey audiance at least to belive it even if it looks A LITTLE CGI. Maybe its to much but i think its doable for me and at least i want to try  The footage will be shot on 20 mm lens. 

Anyway thanks for information it was very helpful and i already started some brainstorming

 

PS. Why your file when i press play it goes so slow? I dont think there is so much infomation to procces that it goes like 5 frames per sec or am i missing something? Im using Houdini 16 so i dont know if it changes anything or what

Edited March 27, 2017 by CatTaker

[vtrvtr]

On 3/27/2017 at 4:10 PM, CatTaker said:

Yeah totaly forgot about some details. Im gona use real footage where i will do camera tracking, HDR ( in case i will need it), and some measurements. Object will be about 50 m from the camera and the ring will be growing from this object up to 30 m. So the closest part of the burning grass will be 20 m. On the edge of the ring there will be a fire (imagine it as a fire ring). Inside a circle there will be a symbol - pentagram with will be also in fire. The symbol will scale proportianolly to the size of the edge circle starting from the beggining of the simulation. Fire of this symbol will be different, less noisy, more calm then the fire on the edge of the circle. It doesnt have to be super realistic but i want to convey audiance at least to belive it even if it looks A LITTLE CGI. Maybe its to much but i think its doable for me and at least i want to try  The footage will be shot on 20 mm lens. 

Anyway thanks for information it was very helpful and i already started some brainstorming

 

PS. Why your file when i press play it goes so slow? I dont think there is so much infomation to procces that it goes like 5 frames per sec or am i missing something? Im using Houdini 16 so i dont know if it changes anything or what

20m seems really far, I don't think you need to worry about the individual grass

As for why is it slow. I don't know. It isn't slow on my machine, pretty much real time. There's really not much in it, the most intensive node there is the vdbfrompolygons, try disabling that

In order to get a nice fallout you need to have a lot of voxel bands (think of it as layers), which makes the vdb process a bit heavy. There are several other ways to transfer the attribute tho, this is certainly not the most efficient one