41 lines
1.6 KiB
Plaintext
41 lines
1.6 KiB
Plaintext
# The Grid subsystem
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The grid subsystem at B401 supplies a set of words on top of
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the Grid protocol (see doc/protocol.txt) that facilitates the
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development of programs presenting a complex text interface,
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for example, the Visual Editor.
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It create the concept of a cursor, always being a some position
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on screen. That position is in the variable XYPOS, which is a
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simple integer following the same "pos" logic as in the Grid
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protocol.
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It implements (emit), which sets the cell under the cursor to
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the specified character, then moves the cursor right. If the
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cursor is at the last column of the screen, it overflows to the
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next line. If it's on the last line, it overflows to the first
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line.
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Grid's (emit) handles 0xd by moving the cursor to the next line
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and 0x8 by moving the cursor left.
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AT-XY ( x y -- ) moves the cursor to the specified position. It
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is equivalent to setting XYPOS directly, but uses separate X
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and y numbers.
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When the grid's cursor enters a new line, it clears its
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contents through a repeated call to CELL!. That implementation
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is in its world named NEWLN ( ln -- ). This word can be over-
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ridden. If it exists when the grid subsystem is loaded, the ex-
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isting NEWLN will be used.
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The clearing of the newly entered line is usually only desirable
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when in "shell" mode. In "graphical" mode, we usually don't
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want this to happen. XYMODE is a flag to indicate whether the
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grid system is in "graphical" mode. When its value is nonzero,
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NEWLN is not called when entering a new line.
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At build time, the Grid subsystem needs 3 bytes of system me-
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mory through the GRID_MEM constant. At run time, GRID$ needs to
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be called to initialize the system.
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