NIC #7124
JUNE 27, 1971
JOHN Mc CONNELL
AMES RESEARCH CENTER
MOFFET FIELD, CALIFORNIA
MODIFICATIONS TO RFC #177
- CATEGORY D.6
-
- RFC's Obsoleted none
-
- RFC's Updated 177
-
[Page 1]
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This RFC is intended to modifiy the proposal for a device
- independent graphical display description discussed in RFC #177. Thanks
-
- are due to Stan Mantiply of Ames for his ideas. The main changes are in
-
- the defini- tion of coordinate areas to avoid one problem encountered
-
- with the old definition and to provide more flexibility. Terms used are
-
- those defined in RFC #177.
-
The problem encountered in the previous proposal was that the areas
- of the NGS (network standard graphics screen), which were supposed to be
-
- absolute boundaries, could be crossed when a list was executed within
-
- that space. Scaling of lists was also awkwardly done with specific
-
- commands in the network standard graphic display list (NGDL).
-
Coordinates will still be defined with 16 bit unsigned normalized
- fractions. This will leave the resolution of the picture up to the de-
-
- vice which eventually receives the NGDL. The values will not now be
-
- tied to the NGS or an area of the screen, but will be fractional
-
- displace- ments from the lower left corner of the screen, an area, or an
-
- image space.
-
Areas will still be rectangular and will be allowed to overlap, but
- not contain another area completely. The attributes of an area are: its
-
- 16 bit integer name, by which it may be manipulated, two (x,y) pairs
-
- which will define its lower left and upper right corners with respect to
-
- the NGS. No list executed in an area may cross its boundaries. Within
-
- an area may be any number of image spaces which are dynamically defined
-
- with the execution of a list and define its relationship to the contain-
-
- ing area.
-
The list item types 7 and 8 shall be changed from EXECUTE LIST
- (Name,x,y) and COPY LIST (Name,x,y) to EXECUTE LIST
-
- (Name,(Xl,Yl),(Xr,Yr)) and COPY LIST (Name,(Xl,Yl),(Xr,Yr))
-
- respectively. The coordinate pairs (Xl,Yl) and (Xr,Yr) define the image
-
- area of that list as displacements from the lower left corner of the
-
- containing area. If the list executes other lists within it, their
-
- image areas are defined as displacements from the image area of the list
-
- containing the execute command. Thus each list can be scaled
-
- differently each time it is executed and may even be distorted if the
-
- image area defined has different ratios of X and Y lengths. Lists
-
- executed within other lists will have the same relationship to their
-
- containing lists regardless of that lists's rela- tionship to the NGS
-
- area. Since the initial image area is defined rela- tive to the NGSD
-
- area, no overlaps can occur.
-
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- contains are relative to whatever area is valid at the time of its exe-
-
- cution.
-
A change to the NGLI is implied. Whenever an EXECUTE LIST command
- is encountered, the current state is saved, a new current origin is com-
-
- puted, NGLP is reset to zero, and new X and Y scale factors must be cal-
-
- culated to transform the coordinates in the new list to actual screen
-
- coor- dinates.
-
Another construct for graphics processing will be added. This is
- the mode stack for each graphics mode. It will be used for saving and
-
- restoring character and vector mode values as lists are recursively exe-
-
- cuted. Four new list items will be added to handle these operations.
-
PUSH CHARACTER MODE (item type = 14)
PUSH VECTOR MODE (item type = 15)
POP CHARACTER MODE (item type = 16)
POP VECTOR MODE (item type = 17)
The DEFINE LIST command (type = 1) shall have its parameters
- changed. It shall have two parameters, a 16 bit integer name, by which
-
- it may be manipulated and referenced, and a 16 bit integer defining the
-
- length of the list in bytes rather than items. This change is intended
-
- to make processing the NGDS easier and will eliminate the TABLE item
-
- (type = 11).
-
The first three list items should have the WORD IMAGE eliminated
- from them, since they are defining NGS areas now.
-
The list command DEFINE IMAGE ARE (type = 2) shall be changed to
- DEFINE AREA for the same reasons.
-
[ This RFC was put into machine readable form for entry ]
[ into the online RFC archives by Gert Doering 6/97 ]
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