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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" are for optional
- writing 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, in seconds. |
- +---------------------------------+-----------------------------------------------------------------------------------------+
- | 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** | A ``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 **EXTENTS** | Color value of corresponding pixel from half resolution pass. Uses linear filter. |
- +-------------------------------+-------------------------------------------------------------------------------------------------+
- | 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. |
- +-------------------------------+-------------------------------------------------------------------------------------------------+
|
