Use vlCreatePath() to create the data path. Its function prototype is

VLPath vlCreatePath(VLServer vlSvr, VLDev vlDev
    VLNode src, VLNode drn) 

This code fragment creates a path if the device is unknown:

if ((path = vlCreatePath(vlSvr, VL_ANY, src, drn)) < 0) {
    vlPerror(_progName);
    exit(1);
}

This code fragment creates a path that uses a device specified by parsing a devlist:

if ((path = vlCreatePath(vlSvr, devlist[devicenum].dev, src,
    drn)) < 0) {
    vlPerror(_progName);
    exit(1);
}

---

Note: If the path contains one or more invalid nodes, vlCreatePath() returns VLBadNode.

---

If you specify VL_ANY as the device when you create the path, use vlGetDevice() to discover the device ID selected. Its function prototype is

VLDev vlGetDevice(VLServer vlSvr, VLPath path)

For example:

devicenum = vlGetDevice(vlSvr, path);
deviceName = devlist.devices[devicenum].name;
printf("Device is: %s/n", deviceName);

For this optional step, use vlAddNode(). Its function prototype is

int vlAddNode(VLServer vlSvr, VLPath vlPath, VLNodeId node)

where

This example fragment adds a source node and a blend node:

vlAddNode(vlSvr, vlPath, src_vid);
vlAddNode(vlSvr, vlPath, blend_node);

Use vlSetupPaths() to set up the data path. Its function prototype is

int vlSetupPaths(VLServer vlSvr, VLPathList paths,
      u_int count, VLUsageType ctrlusage,
      VLUsageType streamusage) 

where

This example fragment sets up a path with shared controls and a locked stream:

if (vlSetupPaths(vlSvr, (VLPathList)&path, 1, VL_SHARE,
    VL_LOCK) < 0)
{
    vlPerror(_progName);
    exit(1);
}

---

Note: The Video Library infers the connections on a path if vlBeginTransfer() is called and no drain nodes have been connected using vlSetConnection() (implicit routing). To specify a path that does not use the default connections, use vlSetConnection() (explicit routing). Chapter 5, “Managing Connections,” explains the use of this function and related requirements.The following rules are used in determining the connections:

---

---

Note: Do not combine implicit and explicit routing.

---

Use vlSelectEvents() to specify the events you want to receive. Its function prototype is

int vlSelectEvents(VLServer vlSvr, VLPath path, VLEventMask eventmask)

where

Table 2-2 lists and describes the VL event masks

For example:

vlSelectEvents(vlSvr, path, VLTransferCompleteMask); 

Event masks can be Or'ed; for example:

vlSelectEvents(vlSvr, path, VLTransferCompleteMask |
      VLTransferFailedMask);

Timing type expresses the timing of video presented to a source or drain. Table 2-4 summarizes dimensions for VL_TIMING.

To specify video input and output formats of the video signal on the physical connector, use VL_FORMAT.

A video packing describes how a video signal is stored in memory, in contrast with a video format, which describes the characteristics of the video signal. For example, the memory source nodes—CC1 and both VGI1 nodes—accept packed video from a VL buffer and output video in a given format.

Packings are specified through the VL_PACKING control on the memory nodes. This control also converts one video output format to another in memory, within the limits of the nodes.

---

Note: On dual-linked VGI1 memory nodes, only native packings are available; no conversions can be performed.

---

Packing types for eight bits per component are summarized in Table 2-6. In this table, the Native To column lists the nodes to which the packing is native; no software conversion is required, so these packings are fastest.

Packing types for ten bits per component are summarized in Table 2-7. The ten data bits are left-aligned within a 16-bit word. The hardware sets the lower six bits to zero before it writes them to memory. When reading from memory, the lower six bits are ignored. All are native to VGI1 memory nodes.

In addition, Indigo² IMPACT Video also supports dual-link AYUAYV, a packed format with three 10-bit components per 32-bit word, with the lowest two bits set to 0. It is native to VGI1 memory nodes. Bits are

---

Note: Other libraries may use different packing names.

---

For example:

VLControlValue val;

val.intVal = VL_PACKING_RGBA_10;
vlSetControl(vlSvr, path, memdrn, VL_PACKING, &val);

If the single-link packings VL_PACKING_RGB_332_P, VL_PACKING_RGB_8, and VL_PACKING_Y_8_P are requested of a memory drain node, the Video Library performs a software conversion to translate the data from a native packing and format. The application receives data in the requested packing and format, although the capture rate may be degraded.

VL_ZOOM controls the expansion or decimation of the video image. Values greater than one expand the video; values less than one perform decimation. Figure 2-1 illustrates zooming and decimation.

---

Note: Indigo2 IMPACT Video screen drain nodes support the full range of VL_ZOOM (7/1, 6/1, 5/1, 4/1, 3/1, 2/1, 1/1, 1/2, 1/3, 1/4, 1/5, 1/6, 1/7, 1/8). Screen source nodes support 1/1 and 1/2. The texture node supports decimation only. The remaining nodes do not support zoom or decimation (the ratio 1/1 only).

---

Figure 2-1. Zoom and Decimation

VL_ZOOM takes a nonzero fraction as its argument; do not use negative values. For example, this fragment captures half-size decimation video to the screen:

val.fractVal.numerator = 1;
val.fractVal.denominator = 2;
if (vlSetControl(server, screen_path, screen_drain_node, VL_ZOOM, &val)){
   vlPerror("Unable to set zoom");
   exit(1);
}

---

Note: For a source, zooming takes place before blending; for a drain, blending takes place before zooming.

---

This fragment captures half-size decimation video to the screen, with clipping to 320 × 243 (NTSC size minus overscan):

val.fractVal.numerator = 1;
val.fractVal.denominator = 2;
if (vlSetControl(server,screen_path, screen_drain_node,
VL_ZOOM, &val))
{
    vlPerror("Unable to set zoom");
    exit(1);
}
val.xyVal.x = 320;
val.xyVal.y = 243;
if (vlSetControl(server, screen_path, screen_drain_node,
VL_SIZE, &val))
{
    vlPerror("Unable to set size");
    exit(1);
}

This fragment captures xsize × ysize video with as much decimation as possible, assuming the size is smaller than the video stream:

if (vlGetControl(server, screen_path, screen_source, VL_SIZE, &val))
{
   vlPerror("Unable to get size");
   exit(1);
}
if (val.xyVal.x/xsize < val.xyVal.y/ysize)
   zoom_denom = (val.xyVal.x + xsize - 1)/xsize;
else
   zoom_denom = (val.xyVal.y + ysize - 1)/ysize;
val.fractVal.numerator = 1;
val.fractVal.denominator = zoom_denom;
if (vlSetControl(server, screen_path, screen_drain_node, VL_ZOOM, &val))
{
   /* allow this error to fall through */
   vlPerror("Unable to set zoom");
}
val.xyVal.x = xsize;
val.xyVal.y = ysize;
if (vlSetControl(server, screen_path, screen_drain_node,
VL_SIZE, &val))
{
   vlPerror("Unable to set size");
   exit(1);
}

VL_SIZE controls how much of the image sent to the drain is used, that is, how much clipping takes place. This control operates on the zoomed image; for example, when the image is zoomed to half size, the limits on the size control change by a factor of 2. Figure 2-2 illustrates clipping.

Figure 2-2. Clipping an Image

For example, to display PAL video in a 320 × 243 space, clip the image to that size, as shown in the following fragment:

VLControlValue value;

value.xyval.x=320;
value.xyval.y=243;
vlSetControl(vlSvr, path, drn, VL_SIZE, &value); 

---

Note: Because this control is device-dependent and interacts with other controls, always check the error returns. For example, if offset is set before size and an error is returned, set size before offset.

---

VL_OFFSET puts the upper left corner of the video data at a specific position; it sets the beginning position for the clipping performed by VL_SIZE. The values you enter are relative to the origin.

This example places the data ten pixels down and ten pixels in from the left:

VLControlValue value;

value.xyval.x=10; 
value.xyval.y=10; 
vlSetControl(vlSvr, path, drn, VL_OFFSET, &value); 

To capture the blanking region, set offset to a negative value.

Figure 2-3 shows the relationships between the source and drain size, offset, and origin.

---

Note: For memory nodes, VL_OFFSET and VL_SIZE in combination define the active region of video that is transferred to or from memory.

---

Figure 2-3. Zoom, Size, Offset, and Origin

An application can request that Indigo² IMPACT Video capture or play back a video stream in a number of ways. For example, the application can request that each field be placed in its own buffer, that each buffer contain an interleaved frame, or that only odd or even fields be captured. This section enumerates the capture types that Indigo² IMPACT Video supports.

A field mask is useful for identifying which fields will be captured and played back and which fields will be dropped. A field mask is a bit mask of 60 bits for NTSC or 50 bits for PAL (two fields per frame). A numeral 1 in the mask indicates that a field is captured or played back, while a zero indicates that no action occurs.

For example, the following field mask indicates that every other field will be captured or played back:

10101010101010101010...

Capture types are as follows:

VL_RATE determines the data transfer rate by field or frame, depending on the capture type as specified by VL_CAP_TYPE, as shown in Table 2-8.

---

Note: Not all rates are supported on all memory nodes; see Appendix C, “Indigo2 IMPACT Video Nodes and Their Controls,” for details. The buffer size must be set in accordance with the capture type, as listed in Table 2-9 later in this chapter.

---

The VL_CAPTURE_NONINTERLEAVED capture type specifies that frame-size units are captured noninterleaved. Each field is placed in its own buffer, with the dominant field in the first buffer. If one of the fields of a frame is dropped, all fields are dropped. Consequently, an application is guaranteed that the field order is maintained; no special synchronization is necessary to ensure that fields from different frames are mixed.

The rate (VL_RATE) for noninterleaved capture is in terms of fields and must be even. For NTSC, the capture rate may be from 2-60 fields per second, and for PAL 2-50 fields per second. Because a frame is always captured as a whole, a rate of 30 fields per second results in the following field mask:

1100110011001100...

The first bit in the field mask corresponds to the dominant field of a frame. Indigo² IMPACT Video waits for a dominant field before it starts the transfer.

If VL_CAPTURE_NONINTERLEAVED is specified for playback, similar guarantees apply as for capture. If one field is lost during playback, it is not possible to “take back” the field. Indigo² IMPACT Video resynchronizes on the next frame boundary, although black or “garbage” video might be present between the erring field and the frame boundary.

The rate during playback also follows the rules for capture. For each 1 in the mask above, a field from the VL buffer is output. During the 0 fields, the previous frame is repeated. Note that the previous frame is output, not just the last field. If there are a pair of buffers, the dominant field is placed in the first buffer.

Interleaved capture interleaves the two fields of a frame and places them in a single buffer; the order of the frames depends on the value set for VL_MGV_DOMINANCE_FIELD (see Table C-5 or Table C-4 in Appendix C for details). Indigo² IMPACT Video guarantees that the interleaved fields are from the same frame: if one field of a frame is dropped, then both are dropped.

The rate for interleaved frames is in frames per second: 1-30 frames per second for NTSC and 1-25 frames per second for PAL. A rate of 15 frames per second results in every other frame being captured. Expressed as a field mask, the following sequence is captured:

1100110011001100....

As with VL_CAPTURE_NONINTERLEAVED, Indigo² IMPACT Video begins processing the field mask when a dominant field is encountered.

During playback, a frame is deinterleaved and output as two consecutive fields, with the dominant field output first. If one of the fields is lost, Indigo² IMPACT Video resynchronizes to a frame boundary before playing the next frame. During the resynchronization period, black or “garbage” data may be displayed.

Rate control follows similar rules as for capture. For each 1 in the mask above, a field from the interleaved frame is output. During 0 periods, the previous frame is repeated.

This option is not applicable to the texture node VL_TEX.

In the VL_CAPTURE_EVEN_FIELDS capture type, only even (F2) fields are captured, with each field placed in its own buffer. Expressed as a field mask, the captured fields are

1010101010101010...

Indigo² IMPACT Video begins processing this field mask when an even field is encountered.

The rate for this capture type is expressed in even fields. For NTSC, the range is 1-30 fields per second, and for PAL 1-25 fields per second. A rate of 15 fields per second (NTSC) indicates that every other even field is captured, yielding a field mask of

1000100010001000...

During playback, the even field is repeated as both the F1 and F2 fields, until it is time to output the next buffer. If a field is lost during playback, black or “garbage” data might be displayed until the next buffer is scheduled to be displayed.

The VL_CAPTURE_ODD_FIELDS capture type works the same way as VL_CAPTURE_EVEN_FIELDS, except that only odd (F1) fields are captured, with each field placed in its own buffer. The rate for this capture type is expressed in odd fields. A rate of 15 fields per second (NTSC) indicates that every other odd field is captured. Field masks are the same as for VL_CAPTURE_EVEN_FIELDS.

The VL_CAPTURE_FIELDS capture type captures both even and odd fields and places each in its own buffer. Unlike VL_CAPTURE_NONINTERLEAVED, there is no guarantee that fields are dropped in frame units. Field synchronization can be performed by examining the UST, the MSC, or the dmedia info sequence number associated with each field.

The rate for this capture type is expressed in fields. For NTSC, the range is
1-60 fields per second, and for PAL 1-50 fields per second. A rate of 30 fields per second (NTSC) indicates that every other field is captured, resulting in the following field mask:

101010101010101010...

Contrast this with the rate of 30 for VL_CAPTURE_NONINTERLEAVED, which captures every other frame.

Field mask processing begins on the first field after the transfer is started; field dominance, evenness, oddness plays no role in this capture type.

Once you have specified frame parameters in a transfer involving memory (or have determined to use the defaults), create a buffer for the video data. In this case, video data is frames or fields, depending on the capture type:

Like other libraries in the IRIX digital media development environment, the VL uses VL buffers. Vl buffers provide a way to read and write varying sizes of video data. A frame of data consists of the actual frame data and an information structure describing the underlying data, including device-specific information.

When a VL buffer is created, constraints are specified that control the total size of the data segment and the number of frame or field buffers (sectors) to allocate.

A head and a tail flag are automatically set in a VL buffer so that the latest frame can be accessed. A sector is locked down if it is not called; that is, it remains locked until it is read. When the VL buffer is written to and all sectors are occupied, data transfer stops. The sector last written to remains locked down until it is released.

All sectors in a VL buffer must be of the same size, which is the value returned by vlGetTransferSize(). Its function prototype is

long vlGetTransferSize(VLServer vlSvr, VLPath path)

For example:

transfersize = vlGetTransferSize(vlSvr, path); 

where transfersize is the size of the data in bytes.

To create a VL buffer for the frame data, use vlCreateBuffer(). Its function prototype is

VLBuffer vlCreateBuffer(VLServer vlSvr, VLPath path,
      VLNode node, int numFrames)

where

For example:

buf = vlCreateBuffer(vlSvr, path, src, 1); 

Table 2-9 shows the relationship between capture type and minimum VL buffer size.

---

Note: For VGI1 memory nodes, real-time memory or video transfer can be performed only as long as buffer sectors are available to the Indigo2 IMPACT Video device.

---

Use vlRegisterBuffer() to register the VL buffer with the data path. Its function prototype is

int vlRegisterBuffer(VLServer vlSvr, VLPath path,
     VLNode memnodeid, VLBuffer buffer)

where

For example:

vlRegisterBuffer(vlSvr, path, drn, Buffer);

To begin data transfer, use vlBeginTransfer(). Its function prototype is

int vlBeginTransfer(VLServer vlSvr, VLPath path, int count,
      VLTransferDescriptor* xferDesc) 

where

Tailor the data transfer by means of transfer descriptors. Multiple transfer descriptors are supplied; they are executed in order. The transfer descriptors are

This example fragment transfers the entire contents of the buffer immediately.

xferDesc.mode = VL_TRANSFER_MODE_DISCRETE;

xferDesc.count = imageCount;
xferDesc.delay = 0;
xferDesc.trigger = VLTriggerImmediate;

This fragment shows the default descriptor, which is the same as passing in a null for the descriptor pointer. Transfer begins immediately; count is ignored.

xferDesc.mode = VL_TRANSFER_MODE_CONTINUOUS;

xferDesc.count = 0;
xferDesc.delay = 0;
xferDesc.trigger = VLTriggerImmediate;

If your application uses a buffer, use various VL calls for reading frames, getting pointers to active buffers, freeing buffers, and other operations. Table 2-10 lists the buffer-related calls.

Figure 2-4 illustrates the difference between vlGetNextValid() and vlGetLatestValid(), and their interaction with vlPutFree().

Figure 2-4. vlGetNextValid(), vlGetLatestValid(), and vlPutFree()

Table 2-11 lists the calls that extract information from a buffer.

---

Caution: None of these calls has count or block arguments; appropriate calls in the application must deal with a NULL return in cases of no data being returned.

---

In summary, for video-to-memory transfer, use

buffer = vlCreateBuffer(vlSvr, path, memnode1);
vlRegisterBuffer(vlSvr, path, memnode1, buffer); 
vlBeginTransfer(vlSvr, path, 0, NULL); 
info = vlGetNextValid(vlSvr, buffer);
/* OR vlGetLatestValid(vlSvr, buffer); */
dataptr = vlGetActiveRegion(vlSvr, buffer, info); 

/* use data for application */
…
vlPutFree(vlSvr, buffer); 

For memory-to-video transfer, use

buffer = vlCreateBuffer(vlSvr, path, memnode1);
vlRegisterBuffer(vlSvr, path, memnode1, buffer); 
vlBeginTransfer(vlSvr, path, 0, NULL); 
buffer = vlGetNextFree(vlSvr, buffer, bufsize); 
/* fill buffer with data */
…
vlPutValid(vlSvr, buffer); 

These calls are explained in separate sections.

VLInfoPtr vlGetNextValid(VLServer vlSvr, VLBuffer vlBuffer)

VLInfoPtr vlGetLatestValid(VLServer vlSvr, VLBuffer vlBuffer) 

int vlPutFree(VLServer vlSvr, VLBuffer vlBuffer)

Sending Frames From Memory to Video

Use vlGetNextFree() to get a free buffer to which to write data. Its function prototype is

VLInfoPtr vlGetNextFree(VLServer vlSvr, VLBuffer vlBuffer, int size)

After filling the buffer with the data you want to send to video output, use vlPutValid() to put a frame into the valid list for output to video (memory to video). Its function prototype is

int vlPutValid(VLServer vlSvr, VLBuffer vlBuffer)

---

Caution: These calls do not have count or block arguments; appropriate calls in the application must deal with a NULL return in cases of no data being returned.

---

void * vlGetActiveRegion(VLServer vlSvr, VLBuffer vlBuffer,
     VLInfoPtr ptr)

DMediaInfo * vlGetDMediaInfo(VLServer vlSvr,
   VLBuffer vlBuffer, VLInfoPtr ptr)

DMImageInfo * vlGetImageInfo(VLServer vlSvr,
   VLBuffer vlBuffer, VLInfoPtr ptr)