subpix(3G)subpix(3G)NAMEsubpix - controls the placement of point, line, and polygon vertices
FORTRAN 77 SPECIFICATION
subroutine subpix(b)
logical b
PARAMETERS
b expects either .FALSE. or .TRUE..
.FALSE. forces screen vertices to the centers of pixels (default).
.TRUE. positions screen vertices exactly.
DESCRIPTIONsubpix controls the placement of point, line, and polygon vertices in
screen coordinates. By default subpix is .FALSE., causing vertices to be
snapped to the center of the nearest pixel after they have been
transformed to screen coordinates. Vertex snapping introduces artifacts
into the scan conversion of lines and polygons. It is especially
noticable when points or lines are drawn smooth (see pntsmo and linesm).
Thus subpix is typically set to .TRUE. while smooth points or smooth
lines are being drawn.
In addition to its effect on vertex position, subpix also modifies the
scan conversion of lines. Specifically, non-subpixel positioned lines
are drawn closed, meaning that connected line segments both draw the
pixel at their shared vertex, while subpixel positioned lines are drawn
half open, meaning that connected lines segments share no pixels.
(Smooth lines are always drawn half open, regardless of state of subpix.)
Thus subpixel positioned lines produce better results when logico or
blendf are used, but will produce different, possibly undesirable results
in 2-D applications where the endpoints of lines have been carefully
placed.
For example, using the standard 2-D projection:
call ortho2(left-0.5,right+0.5,bottom-0.5,top+0.5)
call viewpo(left,right,bottom,top)
subpixel positioned lines match non-subpixel positioned lines pixel for
pixel, except that they omit either the right-most or top-most pixel.
Thus the non-subpixel positioned line drawn from (0,0) to (0,2) fills
pixels (0,0), (0,1), and (0,2), while the subpixel positioned line drawn
between the same coordinates fills only pixels (0,0) and (0,1).
SEE ALSO
linesm, pntsmo
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subpix(3G)subpix(3G)NOTES
This routine does not function on IRIS-4D B or G models.
The IRIS-4D GT and GTX models do not implement subpixel positioned
polygons. They also do not implement subpixel positioned non-smooth
lines.
On the Personal Iris, XS, XS24, XZ, Elan and Extreme, polygons are always
subpixel positioned, regardless of the value of subpix. Subpixel
positioned non-smooth lines are not implemented.
On Indy, Iris Indigo Entry, and XL systems, subpixel positioned non-
smooth lines are drawn closed instead of half-open.
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