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# FALCON/EAGLE user manual 4.62

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is_EnableDDOverlay | Scroll Previous Top Next More

Syntax

INT is_EnableDDOverlay (HIDS hf)

Description

When in DirectDraw mode is_EnableDDOverlay() activates the live overlay mode. In overlay mode three non-visible image buffers are used: Back buffer, overlay buffer and mix buffer. The video image is digitized in the back buffer. The graphics data can be written in the overlay buffer and thus the overlay data is overlaid on the video image in the mix buffer. The mix buffer is then copied to the visible area of the VGA card. The size of the three buffers is: video_x * video_y * color depth (in bytes per pixel). The driver tries to allocate the buffer directly on the VGA card, (making best use of the high speed image transfer that the VGA card can offer) when mixing the three buffers. If the buffer cannot be allocated in the VGA card, then it must be stored in the system memory. The image transfer from the system memory is slower and, depending on the graphics card, sometimes not at all possible. The overlay is not always faded on. It has to be made visible with is_ShowDDOverlay(). As its key color, the overlay uses black, and thus an overlay cannot contain any black color.

Parameters

hf: Frame grabber handle

Return value

IS_SUCCESS, IS_NO_SUCCESS

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