This dialog controls the self-illumination color of the Fire. It also controls the light emitted by the simulator. It is now called "Fire", because that is a more intuitive name. Unlike the diffuse color, which tells what part of the light is reflected, the self-illumination color is an absolute value, which means that the self-illumination color can have values bigger than 1, whereas the diffuse color can't be above 1. Because the self-illumination color can exceed 1, the control is separated in two parts - the color and the brightness (luminance). The final color is obtained by multiplying them both. The light section is more complicated and needs deeper explanation. Why do we need the light section? If we only use the self-illuminated color, the fire will be visible without external lighting, however the objects near the fire will remain black. Seems like GI should solve the problem, but in most cases it does not. Such a case may appear when we have a self-illuminated object that is too small, then the GI rays can't hit it often enough. The light section solves the problem by registering a light object in the scene that the render engine can use to illuminate the diffuse objects in the scene. Because 3ds Max has no area lights interface, Phoenix FD creates multiple point lights in order to produce soft shadows. The lights are placed in the self-illuminated parts of the simulator. Their color and power is also adjusted properly. If the render engine is set to V-Ray, the light object is only one, but contains all the point lights.
Based on (MXS: earg) - the physical value rendered as fire, by default the temperature is taken.
Texture (MXS: etxt) - if the source channel is set to "Texture", this slot specifies the texture.
Reset - resets the settings to their default values.
Modulate (MXS: mod_e) - when the fire is not based on Texture, this checkbox allows the selected channel to be multiplied by the map in the Texture slot.
Light (MXS: al_enable) this section controls the lights added to the scene (see the general section).
Emit if not renderable (MXS: persistlights) - this forces the simulator to emit light even if the
rendering is disabled. Used for compositing, when the fire is rendered in separate pass.
Self shadowing (MXS: selfshadow) - enables self-shadowing of the smoke from the additional lights.
Lights count (MXS: lights) - the number of lights added to the scene. If the render engine is set to V-Ray, only one light is added, however this parameter still plays important role. The light that is used in V-Ray is an area light and its surface is a combination of spheres. Their count is controlled by this parameter. Using V-Ray you can use very low value for this parameter and you will still have soft shadows. With other render engines you need at about 200 point lights in order to have good soft shadows.
Cut off (MXS: al_cutoff) - V-Ray specific, same as VRayLight cutoff parameter
Power multiplier (MXS: lightsmult) - the proper power of the lights is calculated automatically, however it is an approximation. In some cases it's value may significantly differ from the physically accurate one.
Radius multiplier (MXS: radmult) - when rendering with V-Ray, this parameter controls how sharp the shadows are. It may also be used when part of the light surface crosses a wall and produces undesired lighting behind it. For other render engines it is the same as the start parameter of the omni lights.
|Radius multiplier=0.1||Radius multiplier=1||Radius multiplier=4|
Placing (MXS: al_placing) - specifies a placing method for the additional lights.
Simple - the lights are arranged around a cylinder based on the size of the emissive content
Inside - the lights are distributed within the volume of the emissive content
Calculate - calculates the position of the additional lights and shows them in the viewport
This section affects the rendering under V-Ray only.
The parameters below control how many rays have to be traced in order to calculate the lighting. The bigger the count of the rays, the better the result. The rendering, however, will be slower.
For general explanation of how the light sampling works see the V-Ray documentation
Direct (MXS: subdivs) - direct light sampling control. This parameter controls the count of the rays traced from the shaded point toward the fire in order to find the optical passability between them.
GI (MXS: gisubdivs) - indirect light sampling control. This parameter controls the count of the rays traced from the fire to the scene when GI is calculated, for example if you are using a global photon map, this gives the photon count.
Caustic (MXS: csubdivs) - caustic sampling control. Similar to the GI subdivisions, but used when caustics are calculated.
Color (MXS: ecolorx_s, ecolorx_t, ecolorx_v, ecolory_s, ecolory_t, ecolory_v) - the color of the light as a function of the selected channel's value. This color is multiplied by the luminance to achieve the real value that will be used.
Ignore alpha (MXS: no_alpha_e) - switches between physical and detached shading, when checked the detached mode is used. The physical shading mode (not checked) uses the self-illumination color multiplied by the alpha, in this case your fire will depend on the smoke density. By default this option is checked and the self-illumination color is just added to the final result regardless the alpha.
Multiplier (MXS: emult) - general multiplier of the self-illumination color.
Luminance (MXS: epower_s, epower_t, epower_v) - the intensity of the emitted light is determined by the function represented in the diagram control. The argument (X axis) is the value of the selected source channel. The color of the light is set by the gradient control above.