IDirectMusicSynth::Render method (dmusics.h)

Article
12/05/2018

The Render method is called by the synth sink to render to a buffer in the audio stream.

Syntax

HRESULT Render(
  short    *pBuffer,
  DWORD    dwLength,
  LONGLONG llPosition
);

Parameters

pBuffer

Pointer to the buffer to write to

dwLength

Specifies the length of the buffer. The buffer length is expressed in samples, not bytes. The size in bytes of the buffer can vary, depending on the buffer's format, which the synth sets in response to an IDirectMusicSynth::Activate command.

llPosition

Specifies the position in the audio stream. The position is expressed in samples, not bytes. The caller should always increment this value by dwLength after each call.

Return value

Render returns S_OK if the call was successful. Otherwise, the method returns an appropriate error code. The following table shows some of the possible return status codes.

Return code	Description
E_FAIL	Indicates that the method failed.
E_POINTER	Indicates a bad buffer.
DMUS_E_SYNTHNOTCONFIGURED	Indicates that the synth is not open or not properly configured.
DMUS_E_SYNTHINACTIVE	Indicates that the method is not valid when synth is inactive.

Remarks

Typically, a synthesizer manages converting messages into rendered wave data in two processes. In the first, it time stamps the MIDI messages it receives from the application via calls to IDirectMusicSynth::PlayBuffer and places them in its own internal queue. Then, in response to Render, the second process generates audio by pulling MIDI messages from the queue and synthesizing the appropriate tones within the time span of the requested render buffer.

As the synthesizer renders the MIDI messages into the buffer, it calls IDirectMusicSynthSink::RefTimeToSample to translate the MIDI time stamps into sample positions. This guarantees extremely accurate timing (as long as the IDirectMusicSynthSink implementation is well written).

For more information, see the description of the IDirectMusic interface in the Microsoft Windows SDK documentation.

Requirements

Requirement	Value
Target Platform	Desktop
Header	dmusics.h (include Dmusics.h)

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