# InitUI Callback Reference

        RTSHADER_API bool (*RTS_Shader3_InitUI)
        {
            IRTSExecutionState  *in_pExecState,
            void                *in_pParams,
            void                **io_pShaderInstanceData
        }

The InitUI callback function is called when the shader connections change, or one of the specified parameters is changed. This function receives the execution state, the property page parameters, and the shader instance user data.

The parameters that trigger a call to this callback are defined by returning an answer to the GetRequirements function with the two requirement types: `RTS_REQUIRE_PRIMARYINITUIGUID` and `RTS_REQUIRE_SECONDARYINITUIGUID`.

Parameters:

  | in_pExecState | The execution state interface
  | in_pParams | The shader property page parameters

Return values:

  | io_pShaderInstanceData | Pointer to the shader's instance user data

Returns:
  Success/failure

See also:
  IRTSExecutionState, Realtime Shader Callbacks, Execution Flow