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Clouds

To get the most out of trueSKY clouds, learning how the different variables work together is important. Below you will find a description of each different variable, along with some recommended values. If you would rather watch a tutorial video, head over to our YouTube channel for examples, walkthroughs and tips.

Clouds are the leading feature of trueSKY, allowing for real time volumetric clouds to be added seamlessly into any level. This tutorial is about editing the clouds through the use of the Sky Sequencer. A tutorial on the Sky Sequencer can be found here. Alternatively, see Editing with Unity Scripting or Using UE4 Blueprint for engine specific editing.

Main

These setting will alter setting about how and in what are the clouds are generated, as there are variables such as the ray-tracing methods used, the area which they are created within and the resolution at which they are rendered.

Variable Definition Value
Cloudiness How much cloud in the cloud layer. 0.0 to 1.0
Cloudbase Base altitude of cloud layer. -1.0 to 20.0
Layer Height Height of cloud layer, in km. -1.0 to 20.0
Volume Width Width of cloud layer, in km -1.0 to 20.0
Variable Definition Value
Class How the renderer should raytrace Clouds. If you want a layer of Whispy Clouds, set this to Cirrus Standard = 0, Cirrus = 1
Default Slices Number of slices in main view. Between 80 and 255
Grid Width Width of grid Powers of 2 between 16 and 512
Grid height Height of grid Powers of 2 between 1 and 64
Variable Definition Value
Max Cloud Resolution Resolution of clouds, ideally in powers of 2. Recommended values of 512 or 1024 128 to 4096
Max Cloud distance Distance of furthest cloud layer. 100.0 to 500.0
Render Grid X Detail size of grid used to render clouds. Smaller grid means higher quality clouds. 0.01 to 10km
Render Grid Y Detail size of grid used to render clouds. Smaller grid means higher quality clouds. 0.01 to 10km
Default Num Steps Approximate number of raytrace steps. 40 to 300
Amortization How rendering clouds is spread over frames. For 1, all pixels are drawn every frame, for 2, its 2x1, 3 for 3x2 etc. 1 to 8
Cloud Threshold Distance A heuristic distance to discard near depths from depth interpolation, improving accuracy of upscaling. 0.0 to 10.0
Depth Sampling Pixel Range The size of the sampling area, in pixels, in the full-resolution depth buffer. Used to find near/far depths. 0.0 to 4.0
Depth Temporal Alpha The alpha for temporal blending of the solid depth buffer used for cloud rendering. 1.0 is instant. 0.01 to 1.0
Integration Scheme Which method to use for grid rendering. Fixed is good for static, fluffy clouds. Not recommened for flying through Grid or Fixed
Depth Blending If trueSKY should blend clouds with scenery, or draw them in front/behind depending on altitude. Bool
Share Buffers for VR Share Buffer for VR. Bool

Shape

Shape values alter the general look of the clouds, such as how transparent the cloud is. If you have unusual looking clouds or incorrect artefacts, these are the setting to investigate.

The clouds are made up of a base layer, a transition area and the upper layer.

Clouds are thicker on the bottom, so the base layer is almost always the largest, and the transition area is where the base and upper layers meet.

The upper density is a multiplier for the amount of clouds in the upper layer. A value of 1 will produce the same amount of clouds as the base layer.

There are individual settings to help customise each of the different layers, allowing you to create unique but realistic clouds.

By default, the cloud volume repeats at the edges, and the volume width is controlled by the keyframe value Cloud Width. You can change the size of this volume freely, but to increase the size while retaining the same level of detail, you will also need to modify the size of the volumetric grid. For example, to double the size of the volume, select all the 3D cloud keyframes, and double the size of Cloud Width. Select the cloud layer, and increase both the Cloud Grid Width, and the Generation Noise Resolution, by a factor of two.

Variable Definition Value
Max Density Maximum allowed density. 0.0 to 1.0.
Local Density Current density of the clouds. 0.0 to 1.0.
Base layer Maximum density of the clouds. 0.0 to 2.0
Transition Transition from cloudbase to upper cloud. 0.0 to 1.0.
Worley Noise How much Worley noise to apply. 0.0 to 1.0.
Worley Scale Scale of Worley noise. 0.0 to 12.0
Diffusivity How much cloud edges should be diffused. 0.0 to 1.0.
Persistence Fractal persistence for generating clouds. 0.0 to 1.0.
Octaves Number of noise octaves to generate clouds. 1 to 5.
Upper Density Proportion of cloud density retained in upper layer. 0.0 to 1.0.

Wind

Using Wind to create a dynamic sky and moving shadows is an effective way to make an environment feel alive. There are different ways to shift the clouds, however for clouds to move the time must be progressing. Learn how to control time here.

Known Issues

Setting two keyframes to different wind speeds can cause a visual jump in the clouds. Currently recommend setting all keyframes on one layer to the same speed.

Setting wind speed on the Actor will not adjust movement, only visual Churn. Currently being fixed.

Variable Definition Value
Wind Speed (keyframe) Wind speed in m/s. 0.0 to 1000.0
Wind Heading Horizontal cloud movement direction, in degrees. 0.0 to 360.0
Variable Definition Value
Override Wind Whether to apply real-time wind motion. Bool
Variable Definition Value
Wind Speed (trueSKY Object) Wind speed in m/s. Recommended to be similar to the keyframe wind speed to avoid movement errors. 0.0 to 1000.0

Noise

Noise is the best way to make sure your clouds don’t look too flat or repetitive. Values in noise are very sensitive and can produce unusual results if you’re not careful.

Variable Definition Value
Base Factor Proportion of noise applied at cloudbase. 0.0 to 1.0
Amplitude Strength of fractal edge effect. 0.01 to 100.0
Worley Amplitude Wavelength of fractal Worley noise. 0.1 to 10000.0
Sharpness Sharpness applied at boundary. 0.0 to 1.0
Churn Strength of cloud edge churning effect (larger values = more turbulent clouds). 0.001 to 1000.0
Variable Definition Value
Noise Period Fractal noise period, in days. 0.001 to 1000.0
Noise Phase    
Noise Resolution 3D Perlin noise resolution, for cloud generation. Powers of 2 between 4 and 64
Variable Definition Value
Edge Noise Persistence Persistence for edge noise texture. 0.0 to 1.0
Edge Noise Frequency Frequency of edge noise. Powers of 2 between 1 and 16
Edge Noise Texture Size Size of edge noise texture. Powers of 2 between 4 and 64
Edge Noise Wavelength Wavelength of the edge noise. (Great for hiding Grid Patterns) 0.1 to 100
Cell Noise Wavelength Wavelength of Cell Noise 0.1 to 100
Cell Noise Texture Size Size of cell noise texture. Powers of 2 from 16 to 256
Max Fractal Amplitude Strength of edge noise effect. 0.1 to 10

For more tutorials, head to our YouTube Page, where you will find tutorials and showcases of the best trueSKY can do.

Read about how clouds are rendered in trueSKY here.

Still got Questions? Email us at: contact@simul.co