public Class Interpreter

ABSolute value

ADD

USES: loop

logical AND

CALL function

CEILING

Copy the INDEXed element to the top of the stack

CLEAR the entire stack

DELTA exception C1

DELTA exception C2

DELTA exception C3

DELTA exception P1

DELTA exception P2

DELTA exception P3

Returns the DEPTH of the stack

DIVide

DUPlicate top stack element

ELSE

EQual

Function DEFinition

Set the auto_FLIP boolean to OFF

Set the auto_FLIP boolean to ON

FLIP PoinT USES: loop

FLIP RanGe OFF

FLIP RanGe ON

FLOOR

Get Freedom_Vector

Get Projection_Vector

Greater Than

Greater Than or EQual

Instruction DEFinition

IF test

INSTruction Execution ConTRol INSTCTRL[] Code Range 0x8E Pops s: selector flag (int32) value: USHORT (padded to 32 bits) used to set value of instruction_control. Pushes - Sets instruction_control Sets the instruction control state variable making it possible to turn on or off the execution of instructions and to regulate use of parameters set in the CVT program. INSTCTRL[ ] can only be executed in the CVT program. This instruction clears and sets various control flags in the rasterizer. The selector flag determines valid values for the value argument. The value determines the new setting of the raterizer control flag. In version 1.0 there are only two flags in use: Selector flag 1 is used to inhibit grid-fitting. If s=1, valid values for the value argument are 0 (FALSE) and 1 (TRUE). If the value argument is set to TRUE (v=1), any instructions associated with glyphs will not be executed. For example, to inhibit grid-fitting when a glyph is being rotated or stretched, use the following sequence on the preprogram: PUSHB[000] 6 ; ask GETINFO to check for stretching or rotation GETINFO[] ; will push TRUE if glyph is stretched or rotated IF[] ; tests value at top of stack PUSHB[000] 1 ; value for INSTCTRL PUSHB[000] 1 ; selector for INSTCTRL INSTRCTRL[] ; based on selector and value will turn grid-fitting off EIF[] Selector flag 2 is used to establish that any parameters set in the CVT program should be ignored when instructions associated with glyphs are executed. These include, for example, the values for scantype and the CVT cut-in. If s=1, valid values for the value argument are 0 (FALSE) and 2 (TRUE). If the value argument is set to TRUE (v=2), the default values of those parameters will be used regardless of any changes that may have been made in those values by the preprogram. If the value argument is set to FALSE (v=0), parameter values changed by the CVT program will be used in glyph instructions.

JuMP Relative

Jump Relative On False

Jump Relative On True

LOOP and CALL function

Less Than

Less Than or EQual

MAXimum of top two stack elements

MINimum of top two stack elements

Move the INDEXed element to the top of the stack

MULtiply

NEGate

Not EQual

logical NOT

logical OR

PUSH N Bytes PUSH N Words PUSH Bytes PUSH Words

Read Control Value Table

Round Down To Grid

Round OFF

ROLL the top three stack elements

Read Store

Round To Double Grid

Round To Grid

Round To Half Grid

Round Up To Grid

SCAN conversion ConTRoL SCANCTRL[ ] Code Range 0x85 Pops n: flags indicating when to turn on dropout control mode (16 bit word padded to 32 bits) Pushes - Sets scan_control SCANCTRL is used to set the value of the Graphics State variable scan_control which in turn determines whether the scan converter will activate dropout control for this glyph. Use of the dropout control mode is determined by three conditions: Is the glyph rotated? Is the glyph stretched? Is the current setting for ppem less than a specified threshold? The interpreter pops a word from the stack and looks at the lower 16 bits. Bits 0-7 represent the threshold value for ppem. A value of FF in bits 0-7 means invoke dropout_control for all sizes. A value of 0 in bits 0-7 means never invoke dropout_control. Bits 8-13 are used to turn on dropout_control in cases where the specified conditions are met. Bits 8, 9 and 10 are used to turn on the dropout_control mode (assuming other conditions do not block it). Bits 11, 12, and 13 are used to turn off the dropout mode unless other conditions force it. Bits 14 and 15 are reserved for future use. Bit Meaning if set --- -------------- 8 Set dropout_control to TRUE if other conditions do not block and ppem is less than or equal to the threshold value. 9 Set dropout_control to TRUE if other conditions do not block and the glyph is rotated. 10 Set dropout_control to TRUE if other conditions do not block and the glyph is stretched. 11 Set dropout_control to FALSE unless ppem is less than or equal to the threshold value. 12 Set dropout_control to FALSE unless the glyph is rotated. 13 Set dropout_control to FALSE unless the glyph is stretched. 14 Reserved for future use. 15 Reserved for future use. For example 0x0000 No dropout control is invoked 0x01FF Always do dropout control 0x0A10 Do dropout control if the glyph is rotated and has less than 16 pixels per-em The scan converter can operate in either a "normal" mode or in a "fix dropout" mode depending on the value of a set of enabling and disabling flags.

SCANTYPE SCANTYPE[] Code Range 0x8D Pops n: 16 bit integer Pushes - Sets scan_control Pops a 16-bit integer whose value is used to determine which rules the scan converter will use. If the value of the argument is 0, the fast scan converter will be used. If the value of the integer is 1 or 2, simple dropout control will be used. If the value of the integer is 4 or 5, smart dropout control will be used. More specifically, if n=0 rules 1, 2, and 3 are invoked (simple dropout control scan conversion including stubs) if n=1 rules 1, 2, and 4 are invoked (simple dropout control scan conversion excluding stubs) if n=2 rules 1 and 2 only are invoked (fast scan conversion; dropout control turned off) if n=3 same as n = 2 if n = 4 rules 1, 2, and 5 are invoked (smart dropout control scan conversion including stubs) if n = 5 rules 1, 2, and 6 are invoked (smart dropout control scan conversion excluding stubs) if n = 6 same as n = 2 if n = 7 same as n = 2 The scan conversion rules are shown here: Rule 1 If a pixel's center falls within the glyph outline, that pixel is turned on. Rule 2 If a contour falls exactly on a pixel's center, that pixel is turned on. Rule 3 If a scan line between two adjacent pixel centers (either vertical or horizontal) is intersected by both an on-Transition contour and an off-Transition contour and neither of the pixels was already turned on by rules 1 and 2, turn on the left-most pixel (horizontal scan line) or the bottom-most pixel (vertical scan line). This is "Simple" dropout control. Rule 4 Apply Rule 3 only if the two contours continue to intersect other scan lines in both directions. That is, do not turn on pixels for 'stubs.' The scanline segments that form a square with the intersected scan line segment are examined to verify that they are intersected by two contours. It is possible that these could be different contours than the ones intersecting the dropout scan line segment. This is very unlikely but may have to be controlled with grid-fitting in some exotic glyphs. Rule 5 If a scan line between two adjacent pixel centers (either vertical or horizontal) is intersected by both an on-Transition contour and an off-Transition contour and neither of the pixels was already turned on by rules 1 and 2, turn on the pixel which is closer to the midpoint between the on-Transition contour and off- Transition contour. This is "Smart" dropout control. Rule 6 Apply Rule 5 only if the two contours continue to intersect other scan lines in both directions. That is, do not turn on pixels for 'stubs.' New fonts wishing to use the new modes of the ScanType instruction, but still wishing to work correctly on old rasterizers that don't recognize the new modes should: First execute a ScanType instruction using an old mode which will give the best approximation to the desired new mode (e.g. Simple Stubs for Smart Stubs), and then Immediately execute another ScanType instruction with the desired new mode.

Set Control Value Table Cut In

Set Delta_Base in the graphics state

Set Dual Projection_Vector To Line

Set Delta_Shift in the graphics state

Set Freedom_Vector From Stack

Set Freedom_Vector To Projection Vector

SHift Point by the last point USES: loop

SHift Point by a PIXel amount USES: loop

Set LOOP variable

Set Minimum_Distance

Set Projection_Vector From Stack

Set Projection_Vector To Line

Set Reference Point 0

Set Reference Point 1

Set Reference Point 2

Set Single-Width

Set Single_Width_Cut_In

SUBtract

Set freedom and projection Vectors To Coordinate Axis

SWAP the top two elements on the stack

Set Zone Pointer 0

Set Zone Pointer 1

Set Zone Pointer 2

Set Zone PointerS

Write Control Value Table in FUnits

Write Control Value Table in Pixel units

Write Store