3/6/2023 0 Comments Renderman shading rate![]() ![]() Color is currently just controlled via a color swatch, and color/opacity are not affected by temparature or other factors at this time.Ī great resource for fire and smoke shading methods is the course notes from the Siggraph 2011 course Production Volume Rendering. The user opacity value is multiplied by the smoke density from the voxel grid, so it acts as an 'opacity per 1 unit density' control. FumeFX considers a voxel full of smoke to have a value of 1, though these values can be greater than 1 to indicate more dense smoke. The smoke shading process is much simpler than the fire currently the user only has access to a color and opacity control. It is often quite difficult to nail temperatures exactly in a fluid simulation, so the shader also includes the ability to multiply the temperature values up or down by a user controlled value to dial in a look. ![]() FireOi = normalizedSplinePosition * fireOpacityVal A spline curve would also assist with a separate issue where the cooler fire (red) is generally so transparent as to not be visible at all, and I expect to add this in a future version. I would like to extend this functionality in a more elegant way than providing a list of float values for a spline curve. This is not entirely accurate, but is provided to offer more directibility, as it can still sometimes be difficult to dial in the contributions of the fire and smoke. This way, the hotter the fire, the more opaque the fire, and the fire fades off nicely as the temperature cools. float scaleFactor = pow((normalizedSplinePosition),4)*fireExponent Ĭolor fireColor = colorSplineValue * scaleFactor įire opacity control is provided by a user controlled constant, which is multiplied by the normalized position on the temperature gradient. The result of the fourth power is still in the normalized range, and the constant gives the user direct control over the maximum intensity of the fire. I used the normalized temperature of the fire along the color gradient as the base and multiply the result by a user controlled constant. The actual brightness is defined by the Stefan-Boltzmann law, which is quite involved but basically boils down to intensity being proportional to the temperature raised to the fourth power. In my case, I am using a color spline with 10 values approximating the ramp.īrightness of actual fire is often not taken to account in rendering of fire fluid simulations. If fire simulations are conducted with realistic temperature values (or converted later), the black body radiation spectrum can be applied to the fire particles to produce a realistic flame rendering. The soot particles in fire are considered black bodies, and an obvious property of fire fluid simulation is temperature. ![]()
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