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Justifying Text on the Roman Script System

This section describes several important points about the way text is justified

in the Roman Script System:

• The weight for allocating extra space to each nonspace character is in

the form of a percentage. This percentage is given by the

Script Manager's smgrCharPortion global variable as a 4.12

fixed-point number, which can be read with GetEnvirons and set

with SetEnvirons by using the smCharPortion verb. There is no

threshold for initiating intercharacter spacing, so this is not a highly

sophisticated model.

• Every space in a style run is allocated the same amount of extra width

and thus is the same size, whether or not it is at the beginning or end of

the line or the style run.

• For characters that are neither at the beginning nor at the end of the

line, half of the charExtra width is allocated on each side of the

character. Characters that are at the beginning or end of the line are

only allocated half of the charExtra width, which appears on the side of

the character toward the center of the line.

• The Script Manager text justification routines do not automatically

strip trailing spaces. To strip trailing spaces in the last style run on

the line, call the VisibleLength function for the last style run and

pass its return value to these routines as the length of the last run.

The Figure below illustrates this model for the justification of text.

Justification in Roman text

Here's how the Script Manager computes the spacing factors for Roman

text.

At the beginning of the line layout process, the Script Manager bases its

values on information obtained by examining the text and a global variable that

contains the ratio used to allocate space among intercharacter spacing and

interword spacing.

Note: The elements in the equations used subsequently in this

discussion are defined here.

Value Meaning

NumChars The number of nonspace characters in the style run.

NumSpaces The number of space characters in the style run.

CharPortion The weight for allocating slop to intercharacter spacing

versus interword spacing.

SpacePortion 1.0 - CharPortion; the weight for allocating slop to
interword  spacing.

The number of intercharacter spaces in a given style run is not necessarily

the same as NumChars because characters at the beginning or end of the line

are only allocated half an intercharacter space. The styleRunPosition

parameter for the style run must be used to determine NumInterCharSpaces

for the style run.

NumInterCharSpaces equals

• NumChars - 1.0, if styleRunPosition = smOnlyStyleRun
• NumChars - 0.5, if styleRunPosition = smLeftStyleRun
• NumChars - 0.5, if styleRunPosition = smRightStyleRun
• NumChars, if styleRunPosition = smMiddleStyleRun

A total weighted spacing for the style run can then be computed, as follows:

TotWeightedSpace = (NumInterCharSpaces * CharPortion) + (NumSpaces *

SpacePortion)

For Roman text, the NPortionText function returns a value based on

TotWeightedSpace, the font size, and the scaling factors. It is also adjusted by a

factor of 32 for backward compatibility with PortionText results.

NPortionText = TotWeightedSpace * fontSize * ( numer.h/denom.h) / 32.0

By calling NPortionText for each style run on a line, the slop value for the

line can be allocated among each of the style runs on the line to obtain

StyleRunSlop for each style run.

StyleRunSlop equals the amount of slop value allocated to this style run-that

is, the number of pixels by which the style run should be increased or

decreased in width after numerator-denominator scaling has been applied.

Finally, using TotWeightedSpace and StyleRunSlop, the values

MoreSpaceExtra and MoreCharExtra for the style run can be determined-that

is, the extra width for each space character and nonspace character after

numerator-denominator scaling has been applied.

MoreSpaceExtra = (SpacePortion * StyleRunSlop / TotWeightedSpace)

MoreCharExtra = (CharPortion * StyleRunSlop / TotWeightedSpace)

The Figure below demonstrates the capabilities of the Roman justification

routines, DrawJust and NDrawJust, compared to the QuickDraw routines,

DrawText and StdText.

The effects of the Roman justification routines

Referenced by (11):