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# SCNProgramDelegate

The interface for tracking errors that occur when compiling shader source code.

```
protocol SCNProgramDelegate : NSObjectProtocol
```

## Overview

You create and use custom shader programs with the  [`SCNProgram`](/documentation/SceneKit/SCNProgram) class.

## Topics

### Handling Shader Compilation Errors

[`program(_:handleError:)`](/documentation/SceneKit/SCNProgramDelegate/program(_:handleError:))

Tells the delegate that an error occurred when compiling GLSL source code.

[`SCNErrorDomain`](/documentation/SceneKit/SCNErrorDomain)

Identifies an error type defined by the SceneKit framework.

[SceneKit Error Codes](/documentation/SceneKit/1409723-scenekit-error-codes)

### Finding Fragment Opaqueness

[`programIsOpaque(_:)`](/documentation/SceneKit/SCNProgramDelegate/programIsOpaque(_:))

Asks the delegate whether fragments rendered by a program are opaque.

### Binding and Unbinding Values

[`program(_:bindValueForSymbol:atLocation:programID:renderer:)`](/documentation/SceneKit/SCNProgramDelegate/program(_:bindValueForSymbol:atLocation:programID:renderer:))

Invoked on the delegate to let it bind program values and/or associated graphics resources (such as textures) for symbols.

[`program(_:unbindValueForSymbol:atLocation:programID:renderer:)`](/documentation/SceneKit/SCNProgramDelegate/program(_:unbindValueForSymbol:atLocation:programID:renderer:))

Invoked on the delegate to let it unbind program values and/or also unbind associated graphic resources (such as textures).


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