SDI Technologies iH30 Especificaciones descargar pdf (Pagina 54)

Device Feedback

Quadro SDI Output PG-03776-001_v06 | 49

9.1.2 Using the GL_present_video Extension

In the case of applications that utilize glPresentFrameKeyedNV() or

glPresentFrameDualFillNV() provided by the GL_NV_present_video extension, the

number of queued buffers can be determined by subtracting the time at which the buffer

was sent from the time at which the buffer was presented or scanned out and then

divide this value by the presentation interval.

The time at which a buffer is sent can be determined utilizing one of the query functions

below by specifying pname as

GL_CURRENT_TIME_NV.

void GetVideoivNV(uint video_slot, enum pname,

int *params);

void GetVideouivNV(uint video_slot, enum pname,

uint *params);

void GetVideoi64vNV(uint video_slot, enum pname,

int64EXT *params);

void GetVideoui64vNV(uint video_slot, enum pname,

uint64EXT *params);

The current time on the Quadro SDI output device in nanoseconds is then returned in

the value of params.

The present or scanout time for a particular buffer is determined by querying, using one

of the functions above with the query target

GL_PRESENT_TIME_NV, the value of the

query object specified as

beginPresentTimeID in the call to

glPresentFrameKeyedNV() or glPresentFrameDualFillNV(). The value returned is

then the time in nanoseconds that the frame first started scanning out. The results of the

query will not be available until frame starts scanning out. For that reason, it is best to

manage query objects as a circular buffer as outlined in Code Listing 38.

The presentation interval can be determined be subtracting the current present time

from the last present time. The resulting value is the time between the scanout of two

subsequent frames. This time should match the expected time for the chosen video

signal format. For example, the presentation interval for 1080i5994 should be roughly 33

msec while for 720p60 the presentation interval should be 16 msec, and the presentation

for 1080p24 should be approximately 40 msec.

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SDI Technologies iH30 Especificaciones Pagina 54