Reading and writing data

The following instructions make it possible to get and to set a point coordinate, to measure the distance between two points, and to determine the current settings for pixels per em and point size.

Get Coordinate projected onto the projection_vector

GC[a]

Code Range	0x46 - 0x47
a	0: use current position of point p
	1: use the position of point p in the original outline
Pops	p: point number (ULONG)
Pushes	value: coordinate location (F26Dot6)
Uses	zp2, projection_vector

Measures the coordinate value of point p on the current projection_vector and pushes the value onto the stack.

Example

The following example shows that the value returned by GC is dependent upon the current position of the projection_vector. Note that point p is at the position (300,420) in the coordinate grid.

GC[1] 9

The projection_vector is parallel to the line from (0,0) to (300,420)

Sets Coordinate From the Stack using projection_vector and freedom_vector

SCFS[ ]

Code Range	0x48
Pops	value: distance from origin to move point (F26Dot6)
	p: point number (ULONG)
Pushes	–
Uses	zp2, freedom_vector, projection_vector

Moves point p from its current position along the freedom_vector so that its component along the projection_vector becomes the value popped off the stack.

Measure Distance

MD[a]

Code Range	0x49 - 0x4A
a	0: measure distance in grid-fitted outline
	1: measure distance in original outline
Pops	p1: point number (ULONG)
	p2: point number (ULONG)
Pushes	distance (F26Dot6)
Uses	zp1 with point p1, zp0 with point p2, projection_vector

Measures the distance between outline point p1 and outline point p2. The value returned is in pixels (F26Dot6) If distance is negative, it was measured against the projection vector. Reversing the order in which the points are listed will change the sign of the result.

Example:

In the illustration below MD[1] between points 25 and 31 will return a smaller value than MD[0] at 10 pixels per em on a 72 dpi device. The difference is due to the effects of grid-fitting which, at this size, stretches out the counter.

Measure Pixels Per EM

MPPEM[ ]

Code Range	0x4B
Pops	–
Pushes	ppem: pixels per em (ULONG)

This instruction pushes the number of pixels per em onto the stack. Pixels per em is a function of the resolution of the rendering device and the current point size and the current transformation matrix. This instruction looks at the projection_vector and returns the number of pixels per em in that direction.

Measure Point Size

MPS[ ]

Code Range	0x4C
Pops	–
Pushes	pointSize: the size in points of the current glyph (F26Dot6)

Pushes the current point size onto the stack.

Measure point size can be used to obtain a value which serves as the basis for choosing whether to branch to an alternative path through the instruction stream. It makes it possible to treat point sizes below or above a certain threshold differently.

12, 18, and 36 point Helvetica g at 72 dpi