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NETWORK WORKING GROUP REQUEST FOR COMMENTS 181 NIC #7124 JUNE 27, 1971

JOHN Mc CONNELL

AMES RESEARCH CENTER MOFFET FIELD, CALIFORNIA

MODIFICATIONS TO RFC #177

CATEGORY D.6 RFC's Obsoleted RFC's Updated

none 177

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MODIFICATIONS TO RFC #177 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 of the NGS (network standard graphics screen), which absolute boundaries, could be crossed when a list was that space. Scaling of lists was also awkwardly done commands in the network standard graphic display list Coordinates will fractions. This will vice which eventually tied to the NGS or an displace- ments from image space. still be defined with leave the resolution receives the NGDL. area of the screen, the lower left corner 16 of The but of was that the areas were supposed to be executed within with specific (NGDL).

bit unsigned normalized the picture up to the devalues will not now be will be fractional the screen, an area, or an

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 containing 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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If a table (item type = 9) is executed, the coordinate pairs it contains are relative to whatever area is valid at the time of its execution. A change to the is encountered, the puted, NGLP is reset culated to transform coor- dinates. NGLI is implied. current state is to zero, and new the coordinates Whenever an EXECUTE LIST command saved, a new current origin is comX and Y scale factors must be calin the new list to actual screen

Another construct for graphics processing will the mode stack for each graphics mode. It will be restoring character and vector mode values as lists cuted. Four new list items will be added to handle PUSH PUSH POP POP CHARACTER MODE VECTOR MODE CHARACTER MODE VECTOR MODE (item (item (item (item type type type type = = = = 14) 15) 16) 17)

be added. This is used for saving and are recursively exethese operations.

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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