It seems that for italic angle x = 0 is at half the xHeight?!
I get that the editor only shows this as arbitrary value and the hmtx and LSB there that gets compiled are based on the outlines/bounds, which would be tedious to work with in when drawing glyphs. But why is italic x 0 not at the baseline or somewhere more… I don’t know… sensible? How does half xHeight make sense? Am I missing something entirely here?
The idea to have the same horizontal position when having upright and italic next to each other.
You can define your own slant position but I not seen a case that was needed.
My use case was drawing a (skewed) box around the glyph that matches it’s horizontal metrics and vertical extrema (I want to visually compare metrics changes). Maybe it’s useful to someone in the future, the x position origin offset is there in the transformation matrix:
# Create a new path
rectangle_path = GSPath()
# Create nodes for the rectangle (clockwise from bottom-left)
rectangle_path.nodes = [
GSNode((x, y), GSLINE), # Bottom-left
GSNode((x + width, y), GSLINE), # Bottom-right
GSNode((x + width, y + height), GSLINE), # Top-right
GSNode((x, y + height), GSLINE) # Top-left
]
# Close the path
rectangle_path.closed = True
# Skew the rectangle, offset to the left to match 0,0 origin
rectangle_path.applyTransform([
1, # x scale factor
0, # x skew factor
math.tan(math.radians(italicAngle)), # y skew factor
1, # y scale factor
-math.tan(math.radians(italicAngle))*xHeight/2, # x position
0 # y position
])
