REC: shared data segment - Camera & Lighting
(1997R2 camera & light memory formats.)
Document index
Camera section.
Light section.
Data Block diagrams.
The module mcshar_access.c provides interfaces for linking into the two shared memory blocks:
- char * mcshar_camera(int flg) - returns a pointer to the camera block, optionally IPC_CREAT can be passed to create the shared memory area if it does not already exist.
- char * mcshar_light(int flg) - returns a pointer to the lighting block. (with the same flag options)
- void mcshar_detach(void) - remove the current process from the shared memory segments.
These functions are prototyped in mcshare.h as well as all the camera and lighting data structures described below.
Camera information is stored as a position vector (floats) and an orientation quaternion (floats).
typedef struct
{
mc_vector
position;
float
s, i, j, k;
} mc_camera;
In addition, the camera memory area includes signalling flags indicating the current camera number, if changes have been made, and if the current visual in REC is mirrored. The entire memory space of 'MCCM' is thus:
typedef struct
{
long
count,
changecamera,
ismirror;
mc_camera
current;
} mcshare_camera;
REC owns and updates CAMERA and marks CHANGECAM as necessary.
Light information is stored as a mc_ambient record, an array of 24 mc_light records, and associated update/change flags.
Ambient lighting is stored as brightness & color values (float), its structure is:
typedef struct
{
float
i, r, g, b;
} mc_ambient;
Lights include the same color information as well as a four entry position vector (x, y, z, w):
typedef struct
{
float
i, r, g, b;
mc_extvector
position;
} mc_light;
The entire 'MCLT' includes mc_ambient, an array of 24 mc_light elements, a light count, a change flag, and markers for updates in each individual light element:
typedef struct
{
long
count,
changelight;
mc_ambient
ambient;
mc_light
light[24];
unsigned char
marker_ambient[1],
marker_light[24];
} mcshare_light;
Operational Notes
REC initializes the lighting array with its starting configuration and will update the array of lights with reloaded changes if no external tools are running. While it is doing this, it will set count to the negative of the number of lights.
When an external tool connects to this shared memory block and wants to exert control, it needs to do the following:
- Read the current number of lights and lighting array.
- Set count to a positive number.
- Set changelight to one.
At that point, REC will recognize that an external tool is running and discontinue updating the lighting array itself.
Shutdown options
FL shutdown
If an external lighting tool is quiting, it will turn over control of the shared memory segment in the following manner:
- Set count to -N.
- Set changelight to one.
REC shutdown
If REC requires the link to shutdown, it may signal the change through the following protocol:
- Set count to zero.
- Set changelight to negative one.
Any external tool is required to exit at that point. (It may optionally save its current state.)