104 lines
7.2 KiB
Markdown
104 lines
7.2 KiB
Markdown
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# Precision Modes
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## Description
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Shader Graph provides specific [data precision modes](https://en.wikipedia.org/wiki/Precision_(computer_science)) for nodes, graphs, and Sub Graphs to help you optimize your content for different platforms.
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To set the precision of an entire graph, select the [**Graph Settings**](Graph-Settings-Menu) tab in the [Graph Inspector](Internal-Inspector.md) and adjust the **Precision** control. Select a node in your graph and select the **Node Settings** tab in the Graph Inspector to adjust the precision of individual nodes.
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## Precision mode settings
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| Name | Description |
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|------:|------------|
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| Single | This is a high-precision floating point value. The number of bits is platform-specific. For modern desktop computers, it is 32 bits.<br/>This mode is useful for world space positions, texture coordinates, and scalar computations that involve complex functions such as trigonometry, power, and exponentiation. |
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| Half | This is a low-precision floating point value. The number of bits is platform-specific. For modern desktop computers, it is 16 bits.<br/>This mode is useful for short vectors, directions, object space positions, and many high dynamic range colors, but not very strong light sources, such as the sun.|
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| Switchable | This mode is only for Sub Graphs. When you enable this mode for a Sub Graph, the default precision of the Sub Graph is decided by its Sub Graph node. See **Use Graph Precision** below. |
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| Inherit | This mode determines a node's precision based on a set of inheritance rules. See [Precision inheritance](#precision-inheritance).|
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| Use Graph Precision | This mode forces this node to use the same precision setting as the graph.<br/>If this is a node in a Sub Graph, and that Sub Graph’s **Precision** is set to **Switchable**, then the precision of this node is the precision of the Sub Graph node representing this Sub Graph. |
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## Using Precision Modes
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### Visualizing Precision in a graph
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To visualize data precision in a graph, set the [**Color Mode**](Color-Modes.md) control to **Precision**. This applies color coding to your nodes:
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* **Single** nodes are blue
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* **Half** nodes are red
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* **Switchable** nodes are Green.
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### Setting graph Precision
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To set the default precision for the entire graph to **Single** or **Half**, open the **Graph Settings** and set the Precision property. Newly-created nodes in a graph default to the **Inherit** precision mode, and inherit the graph's precision.
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### Setting node Precision
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Select a node to access its precision setting. The precision you set for a node determines the precision of the data types which that node uses for its calculations.
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### Precision Inheritance
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All nodes use the **Inherit** precision mode by default. In this mode, a node that has one or more edge connections takes on the precision mode of an incoming [edge](Edge). Nodes that do not have any edge connections take on **Graph Precision**. If you change the **Graph Precision** mode, the precision of those nodes also changes.
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| **Inputs on the node** | **Final precision determined by inheritance** |
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|------------------------------------|--------------------------------------------|
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| No inputs | **Graph Precision** |
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| Only **Half** inputs | **Half** |
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| Only **Single** inputs | **Single** |
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| **Half** and **Single** inputs | **Single** |
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| Only **Switchable** inputs | **Switchable** |
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| **Switchable** and **Half** inputs | **Switchable** |
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| **Switchable** and **Single** inputs | **Single** |
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| **Switchable**, **Half** and **Single** inputs | **Single** |
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#### Simple inheritance
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Simple inheritance refers to the inheritance behaviour of a node with only one precision type on its inputs.
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In the figure below, Node A has the **Inherit** mode. Because it has no incoming edge, it takes the **Graph Precision**, which is **Half**. Node B also has the **Inherit** mode, so it inherits the **Half** precision mode from Node A.
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#### Complex inheritance
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Complex inheritance refers to the inheritance behaviour of a node with multiple precision types on its inputs.
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A node reads precision settings from each input port. If you connect a node to several others with a variety of precision modes, the node with the highest resolution determines the precision mode for the group.
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In the figure below, node D has the **Inherit** mode. It receives input from the adjacent edges via inputs 1 and 2. Node B passes the **Half** mode through input 1. Node C passes the **Single** mode through input 2. Because **Single** is 32-bit and **Half** only 16-bit, **Single** takes precedence, so Node D uses **Single** precision.
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#### Mixed inheritance
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Mixed inheritance refers to the inheritance behaviour on a node with both simple and complex inheritance types.
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Nodes with no input ports, such as [Input nodes](Input-Nodes), inherit the **Graph Precision**. However, complex inheritance rules still affect other nodes in the same group, as illustrated in the figure below.
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### Switchable precision
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The **Switchable** mode overrides **Half** mode but not **Single**.
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### Sub Graph precision
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Precision behavior and user interface elements for [Sub Graphs](Sub-graph) and their nodes do not differ from other graphs and nodes. Sub Graphs represent a function, and you can affect that function's inputs, outputs, and operators by modifying the relevant set of precision settings.
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* The Sub Graph properties correspond to the function's inputs.
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* The internal node properties correspond to the function's operators.
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* The output node corresponds to the function's outputs.
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#### Outputs
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To manually determine the precision of a Sub Graph's output, modify the **Output** node’s **Precision Mode** setting.
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#### Inputs
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To manually determine the precision of **Sub Graph Inputs**, open the [Graph Inspector](Internal-Inspector) and set precision modes for each individual [Property](Property-Types). Properties that use the Inherit option take on the **Graph Precision** you set for the Sub Graph.
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#### Sub Graph Precision within other graphs
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By default, a Sub Graph has a Precision Mode of `Switchable`. You can modify Precision Mode of any [Sub Graph node](Sub-graph-Node) for that Sub Graph, as long as you set the Precision Mode on the Sub Graph as `Switchable`.
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Shader Graph won't allow you to change the Precision Mode for any Sub Graph node that doesn't have its Sub Graph set to `Switchable`. This is because the input and output precision you set in a Sub Graph define the precision of its associated Sub Graph Node.
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For example, let's say that Sub Graph A is **Switchable**. You open Graph 1, which includes a Sub Graph Node referencing Sub Graph A. Like all other nodes, Sub Graph Node A defaults to **Inherit**. You change the precision of Sub Graph Node A to **Half**. The precision of Sub Graph A also becomes **Half**.
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