The Sky Sequencer
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The Sky Sequencer is a tool for artists, technical artists, level designers, and mission planners. It also helps programmers to understand the workings of True Sky’s sky, clouds and time-of-day systems.

To launch the Sequencer, go to Start Menu/All Programs/Simul/Sky Sequencer/Sky Sequencer.

The Sequencer Window

The Timeline

To change the current time, drag the red vertical line (the time marker) by its handle. To change the visible time-window, drag the timeline at the bottom. To adjust the range of visible time, use the mousewheel to zoom in and out.

To select keyframes, either click on a single keyframe, shift-click to select multiple keyframes, or box-select them. When one or more keyframes are selected, their properties can be changed in the property box. Changing any property affects all selected keyframes of the appropriate type (e.g. all cloud keyframes, or all sky keyframes.)

To select a whole row of keyframes, double-click on the space in-between them.

To select a layer (the sky, a layer of clouds, etc.), click on its name in the column on the left of the timeline.

To add a keyframe, right-click on the timeline and select the “Add sky keyframe…” or “Add cloud keyframe…” option.

Sky keyframes determine the colours of the sky from horizon to zenith, any haze effect, and light colour.

Cloud keyframes determine the properties of the cloud layer at a given time. As the light direction changes with time of day, it is necessary to have enough cloud keyframes to reflect the lighting throughout the day.

Map Window

This window shows the cloud keyframes in a plan view. Wind heading and speed affects the position of each keyframe - or they can be positioned individually. The camera is shown as a red line indicating its direction of view. Rain regions are shown as filled grey circles (blue when highlighted).

Properties Window

The Properties Window can be activated from the Window»Properties menu option. Whatever is selected in the timeline can be edited in the properties window. Its contents depend on the current selection.

When nothing is selected (click on a blank part of the timeline), the general properties are shown, including camera and view properties.

Performance Window

</td> </table> Features ========

Presets

The Sky and Clouds (both 2D and 3D) have various presets available, to quickly set a keyframe to a specific arrangement of values, designed to simulate the desired outcome. Be this a specific type of cloud or just a clear sky. The available presets are, for the Sky: Clear Sky and Fog, for 2D Clouds: Cirrus, Cirrocumulus and Altocumulus and for 3D Clouds: Cumulonimbus, Cumulus, Stratus, Stratocumulus and Altocumulus.

Clouds

In the sequencer, clouds can be edited in two ways. Clicking (or shift-clicking) individual keyframes will allow the properties for one or more keyframes at any point in time to be altered. Alternatively, clicking the 2D Clouds or 3D Clouds column will allow the properties for the respective cloud layer to be altered. Cloud layer properties will impact the entire sequence indefinitely, allowing you to enable/disable cloud rendering, alter the speed of rainfall, change the render mode and more. Whereas keyframe properties are temporal, allowing you to alter cloudiness, rain strength, wind speed and so on, for the point in time at which the keyframe is active. Note: If just a single keyframe is present in the sequencer, then those settings will be applied continously.

Cloud Layer Properties

Note that for 2D clouds, there is no Precipitation section. The cloud layer properties accessible in the sequencer are:

The Performance Window can be activated from the Window>>Performance menu option. When active, this window shows a text display of GPU and CPU profiling data for trueSKY. The GPU data is taken from the DirectX11 view. The values are shown in a hierarchical tree - the time for each element includes the times of its children. The numbers given are times in milliseconds. The colour of the text for each item indicates what percentage of its parent time it occupies. The more red the text, the larger its contribution. You'll see a slight pause in the Sequencer about once per second as the performance window updates - this doesn't affect the measurements.
FeatureDescription
Mode
LoopWhether or not to loop the keyframes.
Keyframe SubdivisionHow keyframes are transitionsed between (real time is simplest).
UpdateWhether to apply updates instantly or gradually. If gradually, any keyframe can be modified at any time. If instant, only the next keyframe can be modified.
NumberIf using fixed intervals, this is the total number of seconds/minutes/days/months.
IntervalInterval between keyframes in minutes/days/months (if game time).
Interval (s)Interval between keyframes in seconds (if real time).
Main
EnabledWhether or not GPU cloud generator should calculate clouds.
Wrap HorizontallyWhether to wrap clouds horizontally.
Overide WindWhether to set wind speed and direction directly, or use the keyframe values.
Render ModeA hint for the renderer on how to raytrace these clouds.
Precipitation
Max ParticlesThe maximum number of rain particles to render.
ThresholdWhat local thickness of cloud is needed for rain to fall, in km.
RadiusSize of the particle zone, in metres.
Rain SpeedSpeed of falling precipitation, in m/s.
Raindrop SizeSize of a single raindrop, in mm.
Rendering
Default SlicesNumber of slices in the main view.
ShadowAmount of shadow between 0 and 1.
Shadow RangeRange of the cloud shadow texture, in km.
Shadow Texture SizeSize of the cloud shadow texture.
Max cloud distDistance of the furthest cloud layer.
Grid
Grid WidthWidth of the grid, in powers of 2 (determines cloud detail).
Grid HeightHeight of the grid, in powers of 2 (determines cloud detail).
Generation Noise
Noise PeriodPeriod in days of the fractal noise function.
Noise PhaseOffset for Noise Period.
Noise ResolutionResolution of the 3D Perlin noise used to generate clouds.
Edge Noise
FrequencyFrequency (power of 2) of the edge noise effect.
ResolutionResolution of the 3D Perlin noise used to generate clouds.
PersistenceFractal persistence to use when generating the noise texture.
See the public attributes of ::clouds::CloudKeyframer CloudKeyframer a full description of all the cloud layer properties.

Cloud Keyframe Properties

Note that for 2D clouds, there is no Weather Effects section. The cloud keyframe properties accessible in the sequencer are:
FeatureDescription
Main
CloudinessHow much cloud in the layer at this time.
CloudbaseBase altitude, in km.
Layer Height How tall the cloud layer is, in km.
Volume WidthThe width of the cloud layer, in km. Typically between 10 and 100.
Wind SpeedWind speed, in m/s.
Wind HeadingWind motion of the clouds, in degrees. Defines the horizontal direction the clouds move in.
Shape
Base LayerProportion of the volume vertically that forms the base of the clouds.
TransitionProportion that transitions from the cloudbase to the upper layer.
Upper DensityDensity of the upper layer as a proportion of the base density.
OctavesHow many fractal octaves to use.
PersistenceFractal persistence.
Worley NoiseHow much Worley (cell) noise to apply in cloud generation.
Worley ScaleScale of the Worley noise. Will be locked to an integer if clouds are wrapping.
DiffusivityHow much the edges of clouds should be diffused.
Lighting
Direct LightThe amount of direct light to be used.
AsymmetryThe anisotropic distribution of direct lighting, or eccentricity.
Indirect LightThe amount of indirect or secondary light to be used.
Ambient LightThe amount of ambient light to be used.
ExtinctionThe amount of light scattered per metre. Larger values produce darker clouds.
GodraysStrength of the godrays effect, between 0 and 1.
Edge Noise
ScaleThe wavelength of the edge noise.
AmplitudeThe strength of the edge noise.
Worley ScaleThe wavelength of the fractal worley edge noise.
Worley AmplitudeThe strength of the fractal worley edge noise.
SharpnessThe sharpness to be applied when rendering the boundary.
Base FactorWhat proportion of noise is applied at the cloudbase, between 0 and 1.
ChurnThe strength of the cloud edge churning effect. Larger values produce more turbulent clouds.
Weather Effects
RegionalIf checked then rain/snow will be limited to the specified region.
Lock to cloudLocks the precipitation region to the cloud wind motion.
Radius (km)The precipitation region, in km.
StrengthHow much rain or snow.
Rain StreaksThe visual strength of the rain-streak effect.
Rain - SnowSet this to 0 for rain, or 1 for snow.
Wind effectStrength of the effect of wind on precipitation direction.
WaverHow much precipitation layers waver as they fall.
See the public attributes of ::clouds::CloudKeyframe CloudKeyframe a full description of all the cloud keyframe properties.

The Sky

In the sequencer, just as with clouds, the sky can be edited in two ways. Clicking (or shift-clicking) individual keyframes will allow the properties for one or more keyframes at any point in time to be altered. Alternatively, clicking the Sky column will allow the properties for the sky layer to be altered. These properties will impact the entire sequence indefinitely, allowing you to adjust the amount of ozone, alter the diameter of the sun/moon, set the start date of the scene and more. Whereas keyframe properties are temporal, allowing you to adjust settings like visibility, haze, eccentricity and so on, for the point in time at which the keyframe is active. Note: If just a single keyframe is present in the sequencer, then those settings will be applied continously.

Brightness Power

The sky at sunrise can be less than one quarter as bright as at noon. Moonlight is hundreds of times dimmer than sunlight. Starlight is much dimmer still. The human eye adjusts to a very wide range of light conditions, but for rendering we usually apply a brightness, or exposure level, to make dark scenes visible and bright scenes clear.
The Brightness Power value for a sky sequence adjusts the light levels to compensate for this large variation by introducing a power function. If the Power is 1.0, there is no adjustment. If it is 0.5, it will be a square-root dependence, e.g. a light 4 times dimmer than daylight would appear only half as dim, and so on.

Automatic Sun and Moon Positions

If these options are enabled, the sun and/or moon can be automatically placed in the sky based on the time, day, month and year. Otherwise, each sky keyframe will have manual position settings.

Colour Sky

A colour sky has colours for sky and fade determined by a choice from a colour dialog. The default behaviour (non-colour sky) is to generate the colours from physical properties).

Sky Layer Properties

Sky layer properties are more general, and will affect all sky keyframes. The sky layer properties accessible in the sequencer are:

FeatureDescription
Atmospheric Scattering Tables
Brightness Power Set the brightness power (see above).
AltitudesThe number of altitudes to calculate / in atmospheric table textures.
Max AltitudeMaximum altitude (km) that will be used for fade and sky colour calculations.
ElevationsNumber of elevations / height of table.
DistancesNumber of distances / width of table.
Distance RangeThe maximum distance for the fade.
Overcast EffectHow strongly the cloud layer blocks light when generating inscatter tables.
Reyleigh CoefficientsRayleigh scattering coeeficients at standard sea level density, xyz = RGB.
Light WavelengthsRed, green and blue wavelengths in nanometres.
The Atmosphere
OzoneThe amount of ozone.
EmissivityThe blackbody emissivity of the atmosphere, between 0 and 1.
Sun
DiameterDiameter of the sun.
Start DateUsed to calculate start positions of sun and moon (if automatic position set).
Latitude & LongitudeThe position of the sun.
Timezone +-Where 0 is GMT.
Link Keyframe time and daytimeWill make daytime value = keyframe value. Otherwise these values are independent.
Moon
AlbedoAlbedo value of the moon (will affect colour).
DiameterDiameter of the moon, in degrees.
TextureTexture to be drawn on moon object.
ColourThe base colour of the moon (will be affected by albedo).
Stars
Max MagnitudeMaximum magnitude of star to be visible. Between 0 (brightest) and 9 (dimmest).
BrightnessBrightness multiplier value.
BackgroundMultiplier for the brightness of cosmic background texture.
Find ConstellationFind a star constellation at given coordinates.
See the public attributes of ::sky::SkyKeyframer SkyKeyframer a full description of all the sky layer properties.

Sky Keyframe Properties

Sky keyframe properties allow you to change particular elements of one or more keyframes at a time. The sky keyframe properties accessible in the sequencer are:
FeatureDescription
Colours
AltitudesNumber of altitudes for use in custom atmospheric table texture.
ElevationsNumber of elevations for use in custom atmospheric table texture.
DistancesNumber of distances for use in custom atmospheric table texture.
Temperature
Sea Level deg. C For infrared rendering.
Haze/Fog/Mist/Dust
Visibility Visibility distance, in km. Fog = <1km, Mist = 1-2km, Haze = >2km. This will alter Haze/fog.
Haze/fog Amount of haze, mist or fog. This will alter Visibility.
Haze base Base altitude above which haze starts to decrease in density, in km.
Haze scale Vertical scale over which haze reduces with altitude, in km.
Eccentricity The anisotropy of Mie scattering.
Mie Coefficients The Mie scattering coefficients, xyz = RGB.
Sun and Moon
HazeHow much haze or fog is present at this time.
Sun azimuthControls the horizontal angle of the sun (if sun position not automatic).
Sun elevationControls how high the sun is in the sky (if sun position not automatic).
Moon azimuthControls the horizontal angle of the moon (if moon position not automatic).
Moon elevationControls how high the moon is in the sky (if moon position not automatic).
See the public attributes of ::sky::SkyKeyframe SkyKeyframe a full description of all the sky keyframe properties.
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