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- .. _doc_fog_shader:
- Fog shaders
- ===========
- Fog shaders are used to define how fog is added (or subtracted) from a scene in
- a given area. Fog shaders are always used together with
- :ref:`FogVolumes <class_FogVolume>` and volumetric fog. Fog shaders only have
- one processing function, the ``fog()`` function.
- The resolution of the fog shaders depends on the resolution of the
- volumetric fog froxel grid. Accordingly, the level of detail that a fog shader
- can add depends on how close the :ref:`FogVolume <class_FogVolume>` is to the
- camera.
- Fog shaders are a special form of compute shader that is called once for
- every froxel that is touched by an axis aligned bounding box of the associated
- :ref:`FogVolume <class_FogVolume>`. This means that froxels that just barely
- touch a given :ref:`FogVolume <class_FogVolume>` will still be used.
- Built-ins
- ^^^^^^^^^
- Values marked as ``in`` are read-only. Values marked as ``out`` can optionally
- be written to and will not necessarily contain sensible values. Samplers cannot
- be written to so they are not marked.
- Global built-ins
- ^^^^^^^^^^^^^^^^
- Global built-ins are available everywhere, including in custom functions.
- +-----------------------------------+------------------------------------------------------------------------------------------+
- | Built-in | Description |
- +===================================+==========================================================================================+
- | in float **TIME** | Global time since the engine has started, in seconds. It repeats after every ``3,600`` |
- | | seconds (which can be changed with the |
- | | :ref:`rollover<class_ProjectSettings_property_rendering/limits/time/time_rollover_secs>` |
- | | setting). It's affected by |
- | | :ref:`time_scale<class_Engine_property_time_scale>` but not by pausing. If you need a |
- | | ``TIME`` variable that is not affected by time scale, add your own |
- | | :ref:`global shader uniform<doc_shading_language_global_uniforms>` and update it each |
- | | frame. |
- +-----------------------------------+------------------------------------------------------------------------------------------+
- | in float **PI** | A ``PI`` constant (``3.141592``). |
- | | A ratio of a circle's circumference to its diameter and amount of radians in half turn. |
- +-----------------------------------+------------------------------------------------------------------------------------------+
- | in float **TAU** | A ``TAU`` constant (``6.283185``). |
- | | An equivalent of ``PI * 2`` and amount of radians in full turn. |
- +-----------------------------------+------------------------------------------------------------------------------------------+
- | in float **E** | An ``E`` constant (``2.718281``). |
- | | Euler's number and a base of the natural logarithm. |
- +-----------------------------------+------------------------------------------------------------------------------------------+
- Fog built-ins
- ^^^^^^^^^^^^^
- All of the output values of fog volumes overlap one another. This allows
- :ref:`FogVolumes <class_FogVolume>` to be rendered efficiently as they can all
- be drawn at once.
- +-------------------------------+-------------------------------------------------------------------------------------------------+
- | Built-in | Description |
- +===============================+=================================================================================================+
- | in vec3 **WORLD_POSITION** | Position of current froxel cell in world space. |
- +-------------------------------+-------------------------------------------------------------------------------------------------+
- | in vec3 **OBJECT_POSITION** | Position of the center of the current :ref:`FogVolume <class_FogVolume>` in world space. |
- +-------------------------------+-------------------------------------------------------------------------------------------------+
- | in vec3 **UVW** | 3-dimensional UV, used to map a 3D texture to the current :ref:`FogVolume <class_FogVolume>`. |
- +-------------------------------+-------------------------------------------------------------------------------------------------+
- | in vec3 **SIZE** | Size of the current :ref:`FogVolume <class_FogVolume>` when its |
- | | :ref:`shape<class_FogVolume_property_shape>` has a size. |
- +-------------------------------+-------------------------------------------------------------------------------------------------+
- | in vec3 **SDF** | Signed distance field to the surface of the :ref:`FogVolume <class_FogVolume>`. Negative if |
- | | inside volume, positive otherwise. |
- +-------------------------------+-------------------------------------------------------------------------------------------------+
- | out vec3 **ALBEDO** | Output base color value, interacts with light to produce final color. Only written to fog |
- | | volume if used. |
- +-------------------------------+-------------------------------------------------------------------------------------------------+
- | out float **DENSITY** | Output density value. Can be negative to allow subtracting one volume from another. Density |
- | | must be used for fog shader to write anything at all. |
- +-------------------------------+-------------------------------------------------------------------------------------------------+
- | out vec3 **EMISSION** | Output emission color value, added to color during light pass to produce final color. Only |
- | | written to fog volume if used. |
- +-------------------------------+-------------------------------------------------------------------------------------------------+
|
