gslop
Purpose
Specifies the logical operation used when drawing lines.
C Syntax
int gslop_ (operation)
int *operation;
FORTRAN Syntax
INTEGER function gslop (operation)
INTEGER operation
Pascal Syntax
FUNCTION gslop_ (
VAR operation INTEGER;
): INTEGER [PUBLIC|;
Description
The gslop subroutine specifies the logical operation used
for drawing the GSL line-oriented, fill, save/restore,
and polymarker primitives. It does not apply to the text
primitives.
Parameters
operation Indicates the logical operation to
perform between the primitive being
drawn and the current contents of the
frame buffer.
In the following table, please note:
o The source pixels represent bits of
data to be merged in some way with
the corresponding bits of data in
the destination rectangle.
o The first three columns of the
table specify the operations you
can perform, and the Code column
contains the corresponding value
you should specify for the opera-
tion parameter.
o A ~ (tilde) represents the logical
INVERSE.
Type of Logical Type of Code
Source Operation Destination
Destination clear 0
Set Destination 15
No operation Destination 5
~Destination 10
Source REPLACE Destination 3
Source AND Destination 1
Source AND ~Destination 2
Source Exclusive-or Destination 6
Source OR Destination 7
Source OR ~Destination 11
~Source REPLACE Destination 12
~Source AND Destination 4
~Source AND ~Destination 8
~Source Exclusive-or Destination 9
~Source OR Destination 13
~Source OR ~Destination 14
Replace (3) is the default logical operation.
Currently, the GSL provides only replace and exclusive-or (codes 3 and 6
respectively) for displays other than the IBM 5081 Display. The full set of
logical operations is supported for the IBM 5081 Display.
For printers and plotters, the operations performed are the same as those for
displays, except that a value of "0" turns the color off, and a value of "15"
changes the color to white.
The GSL performs each of the boolean operations for each bit of the source
and destination color values enabled by the plane mask. The destination
receives the color value that results from the operation.
The logical operations are performed on the color index rather than the color
itself. This can cause some operations on color displays to produce results
that are not expected.
Return Value
GS_SUCC Successful.
GS_LONS Logical operation not supported.