
Graphic Operations
MOTOROLA
MC68322 USER’S MANUAL
12-5
A more complicated graphic operation transfer is calculated in the same way. For example,
the Boolean code for a semi-transparent source transfer onto the destination bitmap
involving halftoning (sometimes used by PostScript) is determined as follows:
Take caution when calculating a Boolean code to ensure only operand values that are
contained in the graphic operation transfer are used. For example, the halftone value should
not be used when specifying the Boolean code for a transfer involving a source/destination
graphic order. If this constraint is violated, the MC68322 treats the extra parameter(s) as
zero. Thus, if the Boolean code for dest = (source
Λ halftone) V dest is used to specify a
transfer involving a source/destination graphic order, the MC68322 treats the halftone
parameter as zero. The resulting operation becomes dest = (source
Λ 0) V dest or simply,
dest = dest.
12.5 BIT BLOCK TRANSFERS
A bit block transfer (bitBLT) is an operation that combines up to three rectangular bit maps
(source, halftone, and destination) in some Boolean combination and places the result in the
original destination bitmap. An expanded bitBLT operation is similar to a standard bitBLT
operation, except that each pixel of the source bitmap is replicated in one or both
dimensions by scaling factors from 1 to 16. An expanded bitBLT graphic order reads an
unexpanded source bitmap directly from memory and expands it to match the resolution of
the destination bitmap. Then it is combined with the destination and/or halftone bitmap to
complete the transfer.
For normal or expanded bitBLT operations, if the destination bitmap is a banded bitmap, the
transfer terminates prematurely if the transfer frame extends below the bottom of the band.
This is considered a band fault. The remainder of the display list is processed in the event
of a band fault, but the transfer operation that caused the band fault will resume when the
display list is rerun to render the next band of the page image.
12.6 SCANLINE TRANSFERS
Scanline transfers are used to operate on nonrectangular regions of bit maps. In their
simplest form, they are used to fill arbitrary polygons and draw vectors. A scanline transfer
involves operating on a specified set of scanline runs on one or more bit maps. The set of
scanline runs is defined by a scanline table, which contains a series of bit string specifiers.
Each bit string specifier is a compressed run-length encoding of a scanline run. The
compressed format of scanline tables not only saves memory, but also improves
performance since fewer memory fetches must be performed.
[(NOT SOURCE)
Λ
DESTINATION]
V
(SOURCE
Λ HALFTONE)
=
BOOLEAN CODE
[(NOT 11001100)
Λ
10101010]
V
(11001100
Λ 11110000)
=
11100010 = E216
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Freescale Semiconductor, Inc.
For More Information On This Product,
Go to: www.freescale.com
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