Frame Offset - This offset is added to the current frame number to determine the frame used for rendering. You can use this to create instances of the container that render with a different frame offset each.
Frame Step - By default the render sequence will be the same as the simulation sequence. If you want to render a simulation in backward order, set this value to -1 and the Frame Offset to the end of the frame range. You can also skip frames by using values larger than 1 (or smaller than -1). Using a values of 0 allows you to freeze a fluid frame while animating the rest of the scene.
Step Size - Specifies the step size as a percentage of a voxel that is used to sample the fluid container. Large values make renders faster but can introduce noise. Smaller values reduce noise but need more time. You should reduce this value only if you see noise artifacts in your renders to avoid increasing the render times unnecessarily.
Shadow Step Size - Shadow rays are usually more robust and produced without noise artifacts. Setting a higher step size for these rays allows you to save render time. This is particularly effective for lit smoke renders.
Interpolation - Specifies the way values are interpolated from the simulation grids. Fast can be somewhat blurry and have banding artifacts. Smooth is the blurriest but avoids banding completely. Sharp avoids blurriness but can have banding artifacts. Note that you can always reduce or even remove blurriness by using steep Mapping curves in the shader settings, even when using Smooth interpolation. Also note that the illumination method (see below) can be the reason for banding as well.
GI Intensity - Scales the intensity of the light emitted from the fluid when rendering with Radiosity enabled.
Use Distance/Opacity Mapping - Enable the mapping of distance from camera to fluid opacity. See below for details.
Distance/Opacity Mapping - Maps the distance from the camera to an opacity for fluid rendering. This can be used when flying the camera through a cloud. Voxels that are very close to the camera may occlude too much of the cloud or they may simply be too big and look blobby. You can fade away their opacity using this mapping.
Channel - Select the simulation channel that you want the shader to use as input.
Smoothing - Blur the field before using it as shader input.
Mapping - This function curve (f-curve) allows you to map the input values to an intensity curve before they are used to determine the smoke's color and opacity. A linear 0 to 1 gradient will leave the values unchanged. To edit the Mapping, click on the curve to open the F-curve editor. See the section on using the f-curve editor for details.
Opacity Channel - To use a separate channel to control the smoke's opacity, select it here. If you use it, the first channel, smoothing and mapping parameters will only control the smoke color. The Smoothing and Mapping parameters below will affect only the opacity.
Thickness - Low values can be used for steam or vapor, high values for thick smoke. Unlike rigid bodies, smoke particles usually do not fill space up completely. Therefore, smoke is always partially transparent. However, the larger the distance that light travels through smoke and the thicker it is, the higher the probability that light rays hit a smoke particle and get scattered or absorbed. That is, while you may be able to look through 1 inch of smoke at thickness 1, 10 inches may be virtually opaque. At thickness 10 however, you may not even be able to look through 1 inch of smoke.
Brightness - The brighter the smoke, the more it will reflect incoming light. You can also adjust the smoke's brightness using the Smoke Color below, but this parameter allows for HDR brightness ranges and is easier to adjust - especially if you have a gradient set for the Smoke Color.
Smoke Color - Defines the smoke color gradient. It assigns colors to re-mapped channel values. The default is to use a single color for all input values (0 to 1) and let only opacity and illumination shade the smoke.
There are two type of render-time sub-grid detail. Both work at render time without requiring a re-simulation.
- Velocity displacement deforms the fluid during rendering and can produce very sharp details.
- Sub-Grid Noise adds detail to the fluid animates over time.
Velocity Displacement works only if a Velocity Cache is available (see Container). Sub-Grid noise works without a Velocity Cache, but for smooth animation you should also have the Velocity Cache available. Both options increase the render time.
Velocity Displacement - Velocity Displacement warps the fluid forward or backward in time, depending on the value you set. Rendering times will be higher, so this is disabled in fast preview mode. Low values can add more detail while introducing very little noticeable deformation. Higher values can change the appearance of the fluid drastically but produce rather interesting effects. Note that you will have to enable Cache Velocity in the Simulation/Cache tab in order to be able to use Velocity Displacement.
Noise Intensity - Specifies how strong the noise will affect the shaded fluid.
Smallest Size - Specifies the size of the smallest noise.
Largest Size - Specifies the size of the largest noise.
Note that the larger the difference between Smallest and Largest scale, more render time will be needed.
Small Power - Specifies how strong small detail is with respect to the next larger ones. A small power of 1.0 will make curls of all sizes equally strong. A small power of 0.5 will make small curls half as strong as curls of twice the size.
Speed - This value specifies how fast the turbulence field changes over time.
Illuminating smoke is the most time-consuming part of a rendering gaseous fluids. TurbulenceFD offers several illumination modes with different speed and quality to choose from. In the list, the speed decreases (first mode is fastest, last mode is slowest) and quality increases (first mode has lowest quality, last mode has best quality).
Note that the default Fast mode may be all you need in many scenes even at high quality requirements. However, the thicker the smoke gets, the more likely you're going to see stairstep artifacts. In these situations, choose the fastest mode that delivers the quality you need.
None - No illumination at all
Fast - Low Quality
Smooth - Medium Quality
Optimal - Slowest, Lowest Memory Usage
Both Corrected modes use more memory with each additional light source that illuminates the fluid container.
Scattering Anisotropy - When light hits a gas it either gets absorbed or bounces off into a different direction. Different types of gases have different preferences of directions into which they scatter light. Water vapor for example tends to scatter light in forward direction. That means that most of the light that hits the vapor does not change its direction too much and continues to travel forward. As a result, the vapor will be brighter when the camera is on the other side of the vapor cloud as the light source.
The Scattering Anisotropy parameter specifies the preferred direction of light scattering. A positive value means forward scattering, a negative value means backward scattering. For example, a value of 1.0 means that the light does not change it's direction at all. You will only see lit smoke if the camera is looking at the light source at the exact angle of the light. Vice versa, a value of -1.0 means that the camera has to look into the same direction as the light to catch any light scattered off the smoke. All light is scattered in exactly the opposite of it's incoming direction.
The neutral value of 0.0 means that light gets scattered into all directions equally.
In practice you would usually only use small values like 0.2 to get brighter backlit smoke for example.
Illumination Resolution - Illuminating smoke takes up most of the render time. You might want to reduce the resolution at which the illumination is computed to save render time. On the other hand, if you have extremely thick smoke, you may see grid artifacts unless you increase the illumination resolution.
Multiple Scattering -Enabling Multiple Scattering allows for two effects.
- It works like Global Illumination for smoke. That is, it computes additional bounces of light inside the smoke, effectively making it brighter. This is the preferred way of creating ambient light. Using the ambient light parameter on the light source will create a low-quality approximation of this effect.
- It allows for the Fire Shader to illuminate the smoke.
Max. Depth -The higher the Depth value, the more bounces will be computed. More bounces will make the smoke brighter but also cost more render time. You can create a cheap approximation of a higher Depth value by lowering the Falloff instead.
Directional Resolution - Increase this value if you see ray artefacts in your smoke. A higher Directional Resolution will increase the render time.
Falloff - The higher this value, the faster the light will fall off as it travels through smoke. You can get brighter smoke by using a lower value here.
Light Brightness - This allows you to separately adjust how much external lights contribute to Mutiple Scattering.
Fire Brightness -This allows you to separately adjust how much brightness the Fire Shader contributes to Mutiple Scattering calculations.
Channel - Select the simulation channel that you want the shader to use as input.
Fire Smoothing - Blur the field before using it as shader input.
Clear Smoke Above - You may want to remove all smoke from the region where fire is shaded to allow for a clearer flame. This value specifies the mapping intensity above which fire will erase smoke for shading.
Mapping - This function curve (f-curve) allows you to map the input values to an intensity curve before they are used to determine the fire color and opacity. A linear 0 to 1 gradient will leave the values unchanged. To edit the Mapping, click on the curve to open the f-curve editor. See the section on using the f-curve editor for details.
Opacity Channel -To use a separate channel to control the fire's opacity, select it here. If you use it, the first channel, smoothing and mapping parameters will only control the fire color. The Smoothing and Mapping parameters below will affect only the opacity.
Opacity - Specifies the opacity of fire. Fire opacity also affects the brightness of the flame. The more glowing particles there are, the more they will obscure the background and the more light will be emitted.
Color Mode - Selects the way the color gradient is defined. Manual Color allows you to specify a color gradient directly, while Black Body Color will use a physical model to compute the color.
Fire Color - Available in Manual Color mode.
If Manual Color Mode is selected, you specify the color gradient here. Make sure that you use a high dynamic range of colors (intensities larger than 100%) and that the Clamp checkbox is not checked.
Luminance - Available in Manual Color mode. Defines the overall color intensity in Manual Mode.
Low Temp. - Available in Black Body mode. In Black Body Color Mode, this value gives the color temperature corresponding to an input value of 0 from the simulation channel. It's most intuitive to observe the gradient above to see this parameter's effect.
High Temp. - Available in Black Body mode. In Black Body Color Mode, this value gives the color temperature corresponding to an input value of 1 from the simulation channel. It's most intuitive to observe the gradient above to see this parameter's effect.
White Point - Available in Black Body mode. Fire has an enormous dynamic range. The white point is used to map it to a lower dynamic range used for you renders. It's most intuitive to observe the gradient above to see this parameter's effect.
Damping - Available in Black Body mode. Instead, or in addition to adjusting the white point, you can damp the dynamic range using this parameter. The higher the value the darker the colors will be.
Red/Green/Blue - Available in Black Body mode. The Black Body color model is an idealization of carbon-based light emission. In real fires plenty of other chemicals are burnt or created during the reaction. These controls let you change the tint of the fire color to allow for a broader spectrum of colors. For example, you may want to add more red (or remove green and blue instead) to get closer to the look of oilier fires.
There are two type of render-time sub-grid detail. Both work at render time without requiring a re-simulation.
- Velocity displacement deforms the fluid during rendering and can produce very sharp details.
- Sub-Grid Noise adds detail to the fluid that animates over time.
Velocity Displacement works only if a Velocity Cache is available (see Container). Sub-Grid noise works without a Velocity Cache, but for smooth animation you should also have the Velocity Cache available.
Both options increase the render time.
Velocity Displacement - Velocity Displacement warps the field forward or backward in time, depending on the value you set. Rendering times will be higher, so this is disabled in fast preview mode. Low values can add more detail while introducing very little noticeable deformation. Higher values can change the appearance of the field very much but produce interesting effects. Note that you will have to enable Cache Velocity in the Simulation/Cache tab in order to be able to use Velocity Displacement.
Noise Intensity - Specifies how strong the noise will affect the shaded fluid.
Smallest Size - Specifies the size of the smallest noise.
Largest Size - Specifies the size of the largest noise. Note that the larger the difference between Smallest and Largest scale, the more render time will be needed.
Small Power - Specifies how strong small detail is with respect to the next larger ones. A small power of 1.0 will make curls of all sizes equally strong. A small power of 0.5 will make small curls half as strong as curls of twice the size.
Speed - This value specifies how fast the turbulence field changes over time.