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Example of using UNITY_DOTS_INSTANCED_PROP macros in a DOTS Instancing shader in URP

An example of using the UNITYACCESSDOTSINSTANCEDPROP to specify if a property can be instanced or not at compile time.
阅读时间3 分钟最后更新于 1 个月前
The 
UNITY_DOTS_INSTANCED_PROP
macro has 3 variants:
  • UNITY_DOTS_INSTANCED_PROP_OVERRIDE_DISABLED(PropertyType, PropertyName)
  • UNITY_DOTS_INSTANCED_PROP_OVERRIDE_SUPPORTED(PropertyType, PropertyName)
  • UNITY_DOTS_INSTANCED_PROP_OVERRIDE_REQUIRED(PropertyType, PropertyName)
These macros allow you to specify if a property can be instanced or not at compile-time. It allows the access macros such as 
UNITY_ACCESS_DOTS_INSTANCED_PROP
to expand to more optimal code and can have significant impact on low-end platforms.
Here is an example of a DOTS Instanced property block using all the macro variants above:
UNITY_DOTS_INSTANCING_START(MaterialPropertyMetadata)    UNITY_DOTS_INSTANCED_PROP_OVERRIDE_SUPPORTED(float4, Color)    UNITY_DOTS_INSTANCED_PROP_OVERRIDE_DISABLED(float4, SpecColor)    UNITY_DOTS_INSTANCED_PROP_OVERRIDE_REQUIRED(float4, EmissionColor)UNITY_DOTS_INSTANCING_END(MaterialPropertyMetadata)
  • The 
    Color
    property can either be instanced or not. The correct loading path is selected dynamically depending on the property metadata high-bit.
  • The 
    SpecColor
    property is not instantiable. This declaration won't add an uint32 field in the constant buffer. It is equivalent to not declaring anything at all. It can be useful to quickly disable instancing on a property without the need to modify other parts of the code.
  • The 
    EmissionColor
    property must be instanced. The property is always loaded from the 
    unity_DOTSInstanceData
    buffer, and no dynamic branch is ever emitted when accessing the property.
By default, 
UNITY_DOTS_INSTANCED_PROP
is the same as 
UNITY_DOTS_INSTANCED_PROP_OVERRIDE_SUPPORTED
. This default behavior can be changed by uncommenting the define 
UNITY_DOTS_INSTANCED_PROP_OVERRIDE_DISABLED_BY_DEFAULT
in "com.unity.render-pipelines.core\ShaderLibrary\UnityDOTSInstancing.hlsl". When you do this, the define is enabled, and 
UNITY_DOTS_INSTANCED_PROP
becomes the same as 
UNITY_DOTS_INSTANCED_PROP_OVERRIDE_DISABLED
.
注意
When uncommenting the define 
UNITY_DOTS_INSTANCED_PROP_OVERRIDE_DISABLED_BY_DEFAULT
, you might need to clear the Library folder to make sure the shaders are correctly recompiled.
On low-end devices, instanced properties can have a significant performance cost. Loading from an SSBO for example, can be a lot slower than a normal constant buffer load. This is because on many low-end devices, this type of buffer load goes through texture samplers, whereas constant buffer loads uses faster hardware unless a dynamic index is used to access the buffer. Instanced properties are always loaded with dynamic indexing since it depends on the property metadata, this means they always go through the texture samplers on low-end devices. To better optimize your project for low-end devices, you can disable property instancing by default. To do this, enable the define 
UNITY_DOTS_INSTANCED_PROP_OVERRIDE_DISABLED_BY_DEFAULT
, this sets property instancing to be disabled as default. Once this is done, you can then enable property instancing manually only for the properties that require it.