--- title: "Render Fire" canonical: "https://documentation.chaos.com/space/PHX4MAX/124629510/Render%20Fire" format: markdown --- This page provides information on the Fire rollout in the Rendering Volumetric Options dialog. > Macro (anchor) ## **Overview** --- This rollout controls the emissive (Fire) color of the volumetric shader, and the light emitted by the simulator. From here you can control the color and intensity of the emission. There are different modes for shading the Fire, which affect whether the Fire and Smoke Opacity shading are linked together, emulating the physical laws of nature, or whether they should be controlled separately for additional flexibility. There is also the [Physically Based](https://docs-chaos.atlassian.net/wiki/spaces/PHX3MAX4EDIT/pages/115087428) parameter, which lets you transition between a more physically correct appearance, giving a stronger brightness to the hot parts of the fire, or a more artistic looking result. > Macro (ui-text-box) > > This customizability allows you to shade a variety of different types of fire, smoke and other volumetric scenarios, from candle flames to fireplaces, to cigarette smoke and massive explosions, as well as sci-fi content such as nebulae, and other effects entirely up to your imagination. In the volume shader, there are two types of content — **diffuse** and **emissive**. For simplicity's sake, we call the diffuse content **Smoke** and the emissive content **Fire**. Diffuse (Smoke) needs external light in order to become visible, and also casts shadows. On the other hand, emissive (Fire) is visible even without being lit by lights. It also ignores their illumination, and does not cast shadows on itself. > Macro (ui-text-box) > > Phoenix has different tools that help you to control how the emissive (Fire) illuminates the Smoke and the scene - see the **[Create Fire Lights](https://docs-chaos.atlassian.net/wiki/spaces/PHX3MAX4EDIT/pages/115087428)** section for more details. Fire and smoke also have their own Color and Alpha. Alpha is a synonym for opacity, and transparency is the opposite of opacity. The **Fire's Color** and **Opacity**, as well as the **Smoke Color** and** Smoke Opacity**, can be mapped to a physical **Grid Channel** from the simulation, using the [Based on](https://docs-chaos.atlassian.net/wiki/spaces/PHX3MAX4EDIT/pages/115087428) parameter. The **Based on** parameter specifies the source channel that will be rendered, and is set independently for the Fire, Smoke Color, and Smoke Opacity respectively. This makes shading very flexible, so that you can even render a simulation's fire as smoke, and smoke as fire, depending on the channel you set the Based on parameter to for each. > Macro (ui-text-box) > > The Fire rollout also contains a **Color Gradient** and **Graph Diagram**, to remap the Grid Channel data to render data. The Color Gradient remaps the Based on channel to a render color, to shade the color of the fire. The Graph Diagram remaps the Based on channel to render either **Fire Opacity** or **Intensity**. > Macro (ui-text-box) > > Fire, Smoke Color, and Smoke Opacity, can also be **mapped to a texture**, or to a Grid Channel multiplied by a texture, to achieve a wide variety of different results. > > Textures have infinite resolution, and so they can increase the detail above the resolution of the grid, meaning that even with a low resolution simulation, you can get a detailed result when using a texture. > > By default, textures are static in space. However, if you export the **Grid Texture UVW Channel** and use the [TexUVW](https://docs-chaos.atlassian.net/wiki/spaces/PHX4MAX/pages/124362975) feature, textures can move together with the fluid to create even more possibilities, such as melting textured icing on a cake. > Macro (rw-ui-expands-macro) > > > Macro (rw-expand) > > ![image](media://6816d8d6-8098-4c94-81ae-ed67b15f3d61) ## **General Parameters** --- > Macro (ui-text-box) > > Using the **Based on** parameter below, you can achieve a wide variety of results when shading **Fire** & **Smoke**. > > For example, the **Fire** (emissive content) is by default based on the **Temperature Grid Channel**. If instead it were based on **Smoke Grid Channel **data, then voxels containing Smoke values would be shaded as emissive (Fire). In other words, the Smoke would be rendered as Fire. > > On the other hand, if the [Smoke Color](https://docs-chaos.atlassian.net/wiki/spaces/PHX4MAX/pages/125312994/Render+Smoke+Color#BasedOn) (diffuse) & [Smoke Opacity](https://docs-chaos.atlassian.net/wiki/spaces/PHX4MAX/pages/125056277/Render+Smoke+Opacity#BasedOn) were based on Temperature, then voxels with Temperature values would be shaded as diffuse volumetrics (Smoke Color & Opacity). In other words, the Fire would be rendered as Smoke.   > Macro (anchor) ## **Light Emission Parameters** --- > Macro (ui-text-box) > > All Fire Lights options are ignored when rendering with V-Ray GPU. Enable Global Illumination from the V-Ray Settings if you need the Smoke and/or the scene to be illuminated by the fire. > Macro (anchor) ### Example: Self-Shadowing --- > Macro (anchor) ### Example: Grid Reduction --- > Macro (anchor) ## **Color** ---   > Macro (ui-text-box) > > When there is both **Smoke** and **Fire** (diffuse and emissive) in the same voxel, you can use the **[Fire Opacity Mode](https://docs-chaos.atlassian.net/wiki/spaces/PHX3MAX4EDIT/pages/115087428)** to determine the resulting color and alpha. > > The Fire can simply use the opacity that is set for the smoke in the [Smoke Opacity rollout](https://docs-chaos.atlassian.net/wiki/spaces/PHX4MAX/pages/125056277/Render+Smoke+Opacity#SmokeOpacity), or you can separate their opacities for additional control, using either the **Fully Visible** or **Use Own Opacity** modes.   ## **Color Gradient and Intensity/Opacity Curve** ---   > Macro (ui-text-box) > > When the **Based on** option is set to a **Grid Channel**, the **Color Gradient** and** Intensity/Opacity curve **graph diagram are used to remap the grid sim data to render data. > > The** Color Gradient** remaps the sim data from the Based on channel to **Fire Color**. > > Meanwhile, the **graph diagram** curve remaps the Based on channel to **Fire Intensity**, or **Fire Opacity **when the **Fire Opacity Mode **is set to **Use Own Opacity**. > Macro (ui-text-box) > > On the graph diagram, **Opacity/Intensity** is mapped vertically on the Y axis, and goes from 0 to 1. > > The X Axis represents the values for the **Grid Channel** selected in the** Based on** parameter. The channel's data range is displayed as a light-blue highlight on the graph. > > See the Phoenix [Grid Channel Ranges](https://docs-chaos.atlassian.net/wiki/spaces/PHX4MAX/pages/125083219) for more information. **Color** | *ecolorx_t, ecolory_t, ecolorx_s, ecolory_s, ecolorx_v, ecolory_v, ecolorx_f, ecolory_f* – Controls the color of the light as a function of the selected channel's value. This color is multiplied by the **Fire Multiplier** to achieve the final value that will be used. The selected channel's data range will be highlighted in light blue. **Intensity** | *epower_t, epower_s, epower_v, epower_f* – Visible when the **Fire Opacity Mode** is set to **Use Smoke Opacity** or **Fully Visible**. The luminance of the emitted light is determined by the function represented in the diagram control. Along the X axis is the value of the selected **Based on** source channel (Temperature, Fuel, etc.). The color of the light is set by the gradient control above. The selected channel's data range will be highlighted in light-blue. **Opacity** | *epower_t, epower_s, epower_v, epower_f *– Visible only when the **Fire Opacity Mode** is set to **Use Own Opacity**. The opacity of the emitted light is determined by the function represented in the diagram control. Along the X axis is the value of the selected **Based on** source channel (Temperature, Fuel, etc.). > Macro (ui-text-box) > > You can use the following controls in the color gradients and diagrams: > > **Double click** – Creates a new point or changes an existing one.** ** > **Left button drag over a point** – Moves the point. If several points were selected beforehand, they will move the same amount. > **Left button drag over several points** – Selects several points. > **Middle button drag over the background** – Drags the visible area. If the Shift key is pressed, scales the diagram in the corresponding direction.** ** > **Mouse wheel** – Zooms in/out. > **Mouse wheel near the borders of the control** – Zooms in/out only along X or only along Y. > **Right click** – Displays a drop-down menu where you can add a point, edit or delete a selected point, and fit the entire diagram or gradient into the view. If multiple points are selected, they can be edited simultaneously.Multiple selected points can also be scaled and flipped with the **Scale Selection** option as seen below. > **Backspace** – Deletes the selected points. > >   > > ![image](media://f4bb675b-153a-42f9-9ce8-99dbc1ab13ff) > Macro (anchor)