logico(3G)

NAME
     logico - specifies a logical operation for pixel writes

FORTRAN 77 SPECIFICATION
     subroutine logico(opcode)
     integer*4 opcode

PARAMETERS
     opcode   expects one of the 16 possible logical operations.

              Symbol      Operation

              LOZERO      0
              LOAND       src AND dst
              LOANDR      src AND (NOT dst)
              LOSRC       src
              LOANDI      (NOT src) AND dst
              LODST       dst
              LOXOR       src XOR dst
              LOOR        src OR dst
              LONOR       NOT (src OR dst)
              LOXNOR      NOT (src XOR dst)
              LONDST      NOT dst
              LOORR       src OR (NOT dst)
              LONSRC      NOT src
              LOORI       (NOT src) OR dst
              LONAND      NOT (src AND dst)
              LOONE       1

              Only the lower 4 bits of opcode are used.

              The values of LOSRC and LODST have been chosen so that
              expressing an operation as the equivalent combination of them
              and the FORTRAN bit manipulation intrinsics generates an
              acceptable opcode value; e.g., LONAND can be written as
              NOT(IAND(LOSRC, LODST)) .

DESCRIPTION
     logico specifies the bit-wise logical operation for pixel writes.  The
     logical operation is applied between the source pixel value (incoming
     value) and existing destination value (previous value) to generate the
     final pixel value.  In colorindex mode all of the (up to 12) writemask
     enabled index bits are changed.  In RGB mode all of the (up to 32)
     enabled component bits are changed.

     logico defaults to LOSRC, meaning that the incoming source value simply
     replaces the current (destination) value.

     It is not possible to do logical operations and blend simultaneously.
     When opcode is set to any value other than LOSRC, the blendfunction
     sfactr and dfactr values are forced to BFONE and BFZERO repectively
     (their default values). Likewise, calling blendf with arguments other
     than BFONE and BFZERO forces the logical opcode to LOSRC.

     Unlike blendf, logico is valid in all drawing modes (NORMDR, UNDRDR,
     OVRDRW, PUPDRW, CURSDR) and in both colorindex and RGB modes.  Like the
     blendfunction, it affects all drawing operations, including points,
     lines, polygons, and pixel area transfers.

     When multiple destination buffers are specified (using frontb, backbu,
     and zdraw ) only a single location is read and used during the logical
     operation.  By default, the destination value is read from the front
     buffer in single buffer mode and from the back buffer in double buffer
     mode.  If the front buffer is not enabled in single buffer mode, the
     value is taken from the z-buffer.  If the back buffer is not enabled in
     double buffer mode, the value is taken from the front buffer (if
     possible) or from the z-buffer.

SEE ALSO
     blendf, gversi, getgde

NOTES
     The numeric assignments of the 16 operation names were chosen to be
     identical to those defined by the X Window System.  They will not be
     changed in future software releases.

     This routine does not function on IRIS-4D B and G models, nor does it
     function on early serial numbers of the Personal Iris.  Use gversi to
     determine which type you have.

     Some IRIS-4D GT and GTX models do support this routine.  Use getgde to
     determine if logico is supported.

BUGS
     Personal Iris models do not support logical operations in combination
     with non-solid patterns nor with zoomed pixel writes or copies.  When
     either of these features is selected, the default logical operation,
     LOSRC, will be used regardless of the value passed to logico.