In otherwords :
- When the destinationmask use (DMU) parame-
ter isset :
- a pel maybe modifiedwhen its mask bit is set
- a pel cannot be modified when its mask bit is
reset.
- When the destinationmask use (DMU) parame-
ter is cleared :
- a pel may be modified, independently of its
maskbit value.
This provides a very flexible clipping mechanism
not restricted to rectangular windows. (See desti-
nation pointer section for destinationmask bit ad-
dressing).
II.3.2 - SOURCE MASK USE (SMU)
APRINTOBJECTcommand may be parametered
for sourcemaskuse.In thiscase, thesourcemask
bit associated with any source pel is read first.
When its mask bit is cleared, a source pel is con-
sideredastransparent.(Seesourcepointersection
for source mask bit addressing).
In otherwords :
- When the SMU parameter is set, the color of a
destination pel, mapped by a given source pel,
may take this source color value only when this
source bit mask is set. The destinationpel keeps
its own color value when the source bit mask is
cleared.
- When the SMU parameter is cleared, a source
pel color may be mapped into destination pel
color independentlyof the sourcebitmask value.
The source bit mask acts as a TRANSPAR-
ENCY/OPACITYflag which is enabled by SMU.A
PRINT OBJECTcommand may be independently
parameteredbybothSMUandDMU.Thisprovides
a very powerfultiling, printobject or move mecha-
nism.
II.4 - DrawingAttributes
01234567
ODD
BANK EVEN
BANK
68483-08.EPS
Figure6 : Color Register
The general drawing attributesare the colors, the
drawing mode, and the scaling factor.
II.4.1. COLORS : Registers R1 andR2
Two 8-bit color values, C0 and C1, may be speci-
fied in registers R1 and R2. The low order 4-bit
nibble of a color value is drawn in an even bank.
Thehighordercolornibbleisdrawninanoddbank.
When long pels are used, banks 0 and 1 are
generally addressed as the frame buffer. When
short pels are used, any bank may hold a frame
buffer.In thiscase, thebankparityselectsthe color
nibble used. (See destination pointer section for
bankaddressing).
II.4.2.DRAWING MODE : RegisterR0
The drawing mode defines the transforms to be
applied to the pels designated by the drawing
commands. Thereare threedrawing modes.
II.4.3.MONOCHROME MODE
Any AREA drawing command, RECTANGLE for
instance, definesthrough its geometricarguments
an active set ofdestinationpels, thatis to saya set
ofpels to be modified.
When DMU = 1, this active set is further reduced
by the masking mechanism to only these destina-
tion pels with a bit mask set.
The active destination pels are then modified ac-
cordingto two elementarytransforms coded in R0.
COLORTRANSFORM :
The color value C of each active pel is modified
according to one color transform selected out of
four :
- 00 - printedin C0 : C ← C0
- 01 - printedin C1 : C ← C1
- 10 - printedin ”transparent” : C← C
- 11- complemented : C← C
This yields to a reversible markermode.
MASK BIT TRANSFORM :
The destination mask bit of each active pel is
modifiedaccordingtoonemask transformselected
out of four :
- 00 - reset bit mask : M ← 0
- 01 - set bit mask : M ← 1
- 10 - no modification: M ← M
- 11- complementbit mask : M ← M
This scheme allows the color bits and the mask bit
ofanypelbelongingtotheactiveset tobemodified
independently. The color transform is performed
first.
II.4.4 - BICHROMEMODE
APRINT CHARACTER commandismore complex
because it involves two different active sets :
FOREGROUND and BACK GROUND.
TheFOREGROUNDis that set of destinationpels
printedfrom set elements in the charactercell.The
BACKGROUND is made of all theremaining pels
belongingto the destinationwindow.
When DMU = 1, the FOREGROUND and BACK
GROUND are further reduced by the destination
masking mechanism(see Figure 8).
A bichromedrawingmodeis definedby 4elemen-
tary and independent transforms (see Fig-
ure 7) :
- a color transform and a mask transform for the
FOREGROUND PELS
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