Day 28

Scroll down to see intro to pyro notes.

When I came into the office, opened firefox on a workstation and visited this blog. The first thing I saw was the schedule and took note of the remaining weeks I have.

That's when I went omgwtfbbq.

I'm wasting no time today perfecting animations and texturing stuff. I can do that whenever where ever.

Okay not really where ever but you get what I mean.

Today I shall start off my pyro simulation tests and also I shall add some upgrades to my sprite particles.

I'll get Evan to look at my finalized animation one last time to officially announce it finalized.

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It's 5.48pm now.

I've just spent the whole day watching recorded pyro fx lectures.

Even though I roughly know the basics of pyro, it's just roughly and not thorough.

Thus I took down as much notes as I could while grasping all the awesome knowledge like a greedy cg grunt.

For anyone who is interested in learning pyro in houdini for the first time, feel free to take a look at this.

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INTRO TO PYRO

Software: Houdini 11

TIP: Turn off all noise for beginners in pyro to see how the fundamentals actually work.

Voxels - 2D pixels that store colour information on a 2D image or 3D cubes that store colour data within a fluid/ gas/ pyro container in 3D space.

Field - The data that is being stored at the voxel locations.

Uniform Divisions - Decides the resolution of the simulation. Default value 50 is very low, 100 is good enough for prototyping.

Visualization Tab

Density - Renders out as smoke.

Heat - Renders out as fire.

Fuel - Needed for combustion to occur and has ignition threshold temperature.

If temperature at a voxel of fuel is higher than ignition temperature, combustion will occur and it will emit smoke. It will also release heat, gas and density. Basically the whole simulation will occur due to fuel thus making fuel very important!

Difference between Hurn and Heat

Burn - Fuel that is combusting at the current moment.

Heat - Product of the combustion releasing heat into the simulation. Based on buoyancy, heat is being advected into the scene.

Fuel => Burn => Heat

To get the good looks

Make sure the heat and density look good in simulation. If heat and density look good in simulation but not in renders, it means the shader must be tweaked.

The simulation data is always the look you want, once fields look good, it's good.

AutoDopNetwork - Pyrosolver

3 main tabs - Sources, Simulation & Advanced.

AutoDopNetwork - Pyrosolver - Sources

Emitters

Emit Fuel - Object is emitter for fuel. Value of fuel amount = multiplication of original fuel amount. More fuel, bigger explosion!

Emit Smoke- Turned off because combustion is already emitting smoke. Turning this on would cause smoke to be emitted from object.

Scale Temperature - Controls how fast fire will rise. Hotter = faster. (It multiplies the original temperature value located in apply-source.)

Noise

Has a 4th dimension - Time.

Prevents pyro simulation from looking too uniformed and makes fire look more chaotic like how it should be.

Gives more variation in fire simulations.

Noise is being emitted from the object. (Can be visualized by checking source in visualization tab)

Ramp can be adjusted and remapped to change noise adjustments and shape.

Note: Candle flames don't need noise since the candle light is calm.

AutoDopNetwork - Pyrosolver - Simulation

Limit Speed - Limits speed of simulation. Use if simulation is going too fast.

Viscosity - Thick volumes of stuff. Not really needed for fire.

Cooling Rate: After 1 second, temperature or voxel field that has a value of 1, after 1 second, it will drop to a value of 90% of that value.

Higher cooling rate gives you more detail on fire. Very high cooling rate example value is 0.01, opposite of what you think. So lower value means higher rate.

Buoyancy: When you have a fluid or gas that has decent high temperature, it looks at the ambient temperature around itself and notices that if it is hotter than the ambient temperature, it will rise.

Buoyancy Lift - Lifts up the simulation process much faster.

Why not just crank up temperature? Because they all work together.

Temperature gives you an initial boost in the beginning.

Buoyancy however is the way gas reacts in reference to the voxel container. (surrounding environment)

Buoyancy Direction - Direction of Buoyancy Lift.

Vortex Confinement - Does the same thing as vorticles but in a slightly different way. It causes simulation to have a little more turbulence in the parts that have turbulence. Always use this as it's good for huge explosions.

Note: Too high vortex confinement will make simulation unstable.

Velocity Damp - Damps velocity field. Use if velocity is going too fast.

Fuel Tab

Advect or don't advect fuel.

If it's turned on, fuel travels along with density and rest of the fields like how it should. Always use for fire.

Fuel Speed -  Value of 1 would emit fuel almost exactly like density. 1 is normally too much of a value.

Combustion Tab

One of the most important tabs in the whole pyrosolver. This is where combustion occurs.

Ignition Temperature: Decides at which temperature simulation is allowed to ignite. It looks at a voxel and if there's fuel in the voxel, it checks if the temperature is higher than the ignition temperature at the voxel. If it is, go into combustion. This occurs at each voxel.

Note: If ignition temperature value is negative, all fuel will instantly ignite.

Burn Rate - The amount of fuel to burn per second. It's a ratio, meaning that at value 0.9, after 1 second, 90% of the fuel will be burnt, leaving 0.1 fuel as leftover.

Burn Rate controls Burn Field, rate at which it burns. Value = amount of fuel to burn per second.

Inefficiency - Gives randomness to the Burning Rate, an uneven sense of fuel burning.

Soot Smoke Rate - Rate of smoke emission. Higher value, more smoke emitted.

Temperature Output - Amount to increase temperature field by. Temperature will go up to the value when combustion is occurring.

Gas Released - Causes density to push out, equivalent to gas pressure.

Heat Source - Burn default recommended.

Heat Cool Time - Time in seconds taken for temperature at voxel to go from value of 1 to 0.

Diffusion Tab

Applies Gaussian blur to the field data (temperature, fuel, density) of a radius of whatever value is in this tab.

Turbulence Tab

Turbulence: Turbulence within whole container domain, manipulating fire simulation. Gives simulation curvy wavy looks.

Scale - Controls how much or little turbulence is affecting simulation. Control differs on how big simulation is.

Bigger simulation = bigger turbulence scale

4th Dimension = Time

Mappings - Remap where turbulence is in turbulence fields.


Forces Tab

Global forces controller for all forces in pyro simulation including gravity.

This applies more force to all force attributes.

Can be remapped like turbulence for more artistic control.

AutoDopNetwork - Apply_source


Sets up some basic source relationships for emitter.

Also has it's own visualization - Guide => Density & SDF

SOP Path & OBJ Path - Object which simulation is emitted from.

Noise - Noise in apply_source multiplies noise from simulation tab. Not recommended for test simulations due to confusion.

Feathering - Blurs out the emitter.

Attribute - For intermediate attribute creation or modifications.

Physical - Temperature: Original temperature value.

Override Velocity - For velocity modifications. Customize using motion effects or others. Controls initial velocity & emission boost time.

SDF Generation

SDF: Signed Distance Field

Value of 1 inside sphere, -1 outside sphere, 0 directly at the surface of the sphere.

Kinda like the distance of the surface which calculates the volume of the geometry.

Note: If source object is moving, check use deforming geometry.

Check Build From Particles - Emit simulation using particle system by using particles as source. Each particles will have fuel, density, heat etc emitting from it. Emission amount can be controlled using Particle to Field (Scale by Voxel Volume) tab.

UPRES PYRO

Use for finer details.

UPRES - Takes low resolution simulation motion and converts it to high resolution. Simulation performs way faster than when increasing the amount of uniform divisions.

Switch_simulationmode

Low Res: Low Res

Both : Does low res than high res afterward, 1 frame at a time.

Up Res : Up Res

What's the best way to up res pyro?

Go into low res pyro obj

Export to File (Just like rendering)

1) Cache, cooks & exports out low res pyro simulation.

2) Once done, check load from disk.

3) Turn off low res obj, turn on up res obj.

4) Go into up res pyro obj - Render & cache up res simulation. Use this for final rendering. (Note: Rename output files to prevent overwrite issues.)

Note: In AutoDopNetwork, go to upres pyro visualization & crank up uniform divisions. Usually recommended use values of low res divisions multiplied by 2 to 3 times.

e.g. low res divisions = 50 thus, high res divisions = 100 or 150

Rendering

Depth Map Shadows

Crank up pixel samples if pyro simulation shadows screw up.

Mantra Node

Sampling Tab - Volume Step Size controls quality of render for volumed simulations.