Microsoft DirectX 9.0


The UseScanLine method determines whether the renderer should check the current scan line when drawing a video.


HRESULT UseScanLine(
  long UseScanLine



Long integer value that specifies whether or not to use the scan line information. Set to OATRUE to use scan line information or OAFALSE to ignore it.

Return Values

Returns E_INVALIDARG if the argument is invalid or S_OK otherwise.


If you blit an image to the video memory while the monitor's scan line is scanning over a visible portion of the screen, the complete image will be a composite of the old and new images. This composite is known as a torn video image. You can avoid torn images by waiting until the previous image is complete before blitting the new image. Some video cards can retrieve the scan line's current position; if this information is available, you can have DirectShow try to reduce tearing by waiting until the scan line is off-screen before blitting the new image. Note that checking the scan line location increases load on the processor and can reduce the amount of video frames delivered to the screen. If scan line information is available, DirectShow uses it by default. Set UseScanLine to OAFALSE if you want to save processing time at the expense of minor image degradation.

See Also