Aqsis Renderer Freedom to Dream

API Reference

API Reference

Aqsis expects a display to implement the standard display interface as in PRMan and other renderers. This means implementing the four functions DspyImageOpen, DspyImageQuery, DspyImageData and DspyImageClose. The function prototypes are defined in the header <ndspy.h>.

All functions in the display interface return one of the possible [[#PtDspyError|error codes]], which will normally be PkDspyErrorNone when everything is ok. The first parameter to the display interface functions is an image handle of type [[#PtDspyImageHandle]]. The handle should be used by the display driver to store internal data associated with the display. Any handle stored here by DspyImageOpen will be passed on to the other functions without being modified by the renderer.


PtDspyError DspyImageOpen(PtDspyImageHandle*   image,
                          const char*          drivername,
                          const char*          filename,
                          int                  width,
                          int                  height,
                          int                  paramCount,
                          const UserParameter* parameters,
                          int                  formatCount,
                          PtDspyDevFormat*     format,
                          PtFlagStuff*         flagstuff);

DspyImageOpen is called by the renderer to open and initialize a display. Typically this might involve allocating a memory buffer large enough to hold the image, opening a file or initializing a GUI to display the data directly.


  • image - a pointer to a handle for any internal data structures allocated by the display. This handle should be set by DspyImageOpen and will be stored by the renderer without modification to be passed on to the other display functions.
  • drivername - the name of the display driver as it was specified in the RiDisplay() call.
  • filename - the output file name as given in the RiDisplay() call.
  • width/height - the image resolution in pixel. When the image is cropped this is the cropped size. Either value may be 0 in which case the driver has to choose an appropriate default value.
  • paramCount - the number of parameters stored in the array parameters.
  • parameters - Parameters to the RiDisplay() interface call are passed on to the display inside this array. For each parameter there is a UserParameter struct that contains the name/value pair. Important note: These structs are only valid within this function. If you need a value in one of the other functions you must copy the value! In addition to the user-defined parameters, there are a number of parameters the renderer always sends to the driver (see table below).
  • formatCount - the number of items in the array format, that is, the number of channels of pixel data in the image.
  • format - For each output channel, there is a PtDspyDevFormat struct describing the type of the data that gets passed into the driver. The driver may rearrange this array or change the data type to get the channels delivered in a different order or as a different type or in a different byte order. If you want to remove a channel, set its type to PkDspyNone. Important notes: 1) When you reorder the array you must ensure that the names still point to the original strings that were passed in! 2) Just like the parameters array the format structs are only valid inside this call. Do not try to access the values again in one of the other functions.
  • flagstuff - The display may change the value of these flags to modify aspects of the incoming pixel data, such as to request that the renderer send scanline order. See PtFlagStuff for possible values.

In addition to any user parameters passed to the driver, the array parameters will always contain the following system-defined parameters:

name vtype[vcount] Description
“NP” f[16] World to screen space matrix
“Nl” f[16] World to camera space matrix
“near” f[1] Near clipping plane
“far” f[1] Far clipping plane
“origin” i[2] Origin of the crop window within the entire image
“OriginalSize” i[2] Original pixel size of the entire image (not just the cropped window)
“PixelAspectRatio” f[1] The pixel aspect ration
“Software” s[1] The name of the renderer
“HostComputer” s[1] The network name of the computer that the image is rendered on


typedef struct
    RtToken   name;
    char      vtype;
    char      vcount;
    RtPointer value;
    int       nbytes;
  • name - the name of the parameter
  • vtype - the type of the parameter value. This can be either "i" for integers of type RtInt, "f" for floats of type RtFloat or "s" for strings of type char*.
  • vcount - this is the array size. If the value is a scalar, vcount is 1.
  • value - this is a pointer that points to the value(s). The display should cast this pointer to the appropriate type to access the contained data.
  • nbytes - the total number of bytes used by the entire value
typedef struct
    char *name;
    unsigned type;
  • name - the name of the output channel. Standard channels include "r", "g", "b", "a", "z", but name may take other values when using AOV.
  • type - one of the possible [[#Pixel types|PkDspy constants]] describing the channel bitwidth and type. The type can be combined (using the bitwise OR operator) with the following flags to determine the byte order of a single value. Obviously this is only meaningful for types that are longer than a single byte.
    • PkDspyByteOrderHiLo: Force big endian format (most significant bytes first)
    • PkDspyByteOrderLoHi: Force little endian format (least significant bytes first)
    • PkDspyByteOrderNative: Use whatever format is native on the current machine (this is the default)
Pixel types

A set of integer constants is defined to specify the output pixel format type. All such constants start with the prefix Pk. Associated with these is a set of typedefs starting with the prefix Pt. Pixel formats are defined both for floating point and signed/unsigned integers of different bit-widths. The value PkDspyNone may be set by the display to remove a channel from the data sent to the driver. For example, if the display can only handle rgb images, but the renderer is going to create rgba data, the display should set the type for the "a" field to PtDspyNone.

Format constant typedef
PkDspyNone -
PkDspyFloat32 PtDspyFloat32
PkDspyUnsigned32 PtDspyUnsigned32
PkDspySigned32 PtDspySigned32
PkDspyUnsigned16 PtDspyUnsigned16
PkDspySigned16 PtDspySigned16
PkDspyUnsigned8 PtDspyUnsigned8
PkDspySigned8 PtDspySigned8
typedef struct
    int flags;

flags is a bitwise or of the following constants:

  • PkDspyFlagsWantsScanLineOrder - Send the data in scanline order rather than as buckets. Scanline order starts from the top-left of the image, working downward line by line. Note that the display shouldn’t assume that a whole scanline will arrive at once.
  • PkDspyFlagsWantsEmptyBuckets - Send pixel data even for buckets which contain no primitives.
  • PkDspyFlagsWantsNullEmptyBuckets - Generate calls to DspyImageData for empty buckets, but set the associated data pointer to null.


PtDspyError DspyImageQuery(PtDspyImageHandle image,
                           PtDspyQueryType   type,
                           size_t            size,
                           void*             data);

This function is used by the renderer to obtain further information about the image or the display driver itself. Aqsis passes in the image handle that was initialised in the open function (or NULL if the query does not relate to a particular image), a query type that determines what kind of information is requested and a data block that has to be filled in by the driver with appropriate values.

  • image - this is either the image handle that was returned in [[#DspyImageOpen|DspyImageOpen]] or a NULL pointer.
  • type - determines the type of information that is requested. The possible types are defined in the enum [[#PtDspyQueryType|PtDspyQueryType]].
  • size - the size in bytes of the memory that data points to. Make sure not to write beyond this size!
  • data - an allocated memory buffer of size bytes that has to be filled in by the display driver. Depending on the query type this points to an appropriate info struct (see below).

The following requests may be made by the renderer:

  • PkSizeQuery: The renderer wants to know the pixel size of an image and the pixel aspect ratio (when image is NULL, default values have to be returned). The values have to be filled into a [[#PtDspySizeInfo|PtDspySizeInfo]] structure and copied to data.

  • PkOverwriteQuery: This is used to query the driver whether it will overwrite an image file or not. For this query, data should receive a [[#PtDspyOverwriteInfo|PtDspyOverwriteInfo]] struct with the return value.


typedef enum
} PtDspyQueryType;

These are the query types that may be encountered by the driver in DspyImageQuery.

Note: PkSupportsCheckpointing and PkRenderingStartQuery are currently not supported by Aqsis.

typedef struct
    PtDspyUnsigned32 width;
    PtDspyUnsigned32 height;
    PtDspyFloat32 aspectRatio;

This struct has to be returned in a query of type PkSizeQuery.

  • width: The image width in pixel
  • height: The image height in pixel
  • aspectRatio: The pixel aspect ratio
typedef struct
    PtDspyUnsigned8 overwrite;
    PtDspyUnsigned8 interactive;

This struct has to be returned in a query of type PkOverwriteQuery.

  • overwrite: A boolean indicating whether the driver will overwrite an image or not
  • interactive: Unused (set this to 0).


PtDspyError DspyImageData(PtDspyImageHandle    image,
                          int                  xmin,
                          int                  xmaxplus1,
                          int                  ymin,
                          int                  ymaxplus1,
                          int                  entrysize,
                          const unsigned char* data);

DspyImageData passes image pixel data from the renderer to the display device.


  • image - handle to display internal data structures.
  • xmin,ymin - minimum x- and y-coordinates for the data. This may be thought of as the top-left of the bucket.
  • xmaxplus1,ymaxplus1 - maximum x- and y-coordinates for the data, plus one. This means that the chunk width is xmaxplus1-xmin and the height is ymaxplus1-ymin.
  • entrysize - the stride between pixel entries in the data array. The pointer (data+entrysize) points to the start of the data for the second pixel.
  • data - a pointer to the raw data. The pixel data is stored with scanlines contiguous in memory, such that data points to the top-left of the chunk.


PtDspyError DspyImageClose(PtDspyImageHandle image);

DspyImageClose closes the display and frees any associated resources such as memory or file handles.


PtDspyError DspyImageDelayClose(PtDspyImageHandle image);

This function is similar to [[#DspyImageClose|DspyImageClose]] but it is executed in a separate process. This is useful for interactive display drivers that want to remain active even though the renderer has finished rendering the image.

Additional API Types

The following additional types are defined by the display API.


typedef enum

All functions from the display driver interface are required to return a value of type PtDspyError that indicates whether the function ran successfully or not. The meaning of the values is as follows:

  • PkDspyErrorNone: The function ran without errors
  • PkDspyErrorNoMemory: The function failed to allocate memory
  • PkDspyUnsupported: An unsupported operation was requested
  • PkDspyBadParams: The driver received invalid parameters
  • PkDspyErrorNoResource: A required resource was not available (such as a file, etc.)
  • PkDspyErrorUndefined: No other error code was applicable


typedef void* PtDspyImageHandle;

The type of an image handle is known only to the display driver which uses it to store state information between display interface function calls. The renderer treats this as an opaque pointer.