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[question] position of first baseline? #105

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frankrolf opened this issue May 23, 2017 · 15 comments
Closed

[question] position of first baseline? #105

frankrolf opened this issue May 23, 2017 · 15 comments
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@frankrolf
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In a text box, how does DrawBot specify the position of the first baseline for a given font?
I am currently working on a script that layers different fonts, and need to calculate the baseline offset – unfortunately that’s trickier than expected.

A common assumption is just subtracting the hhea.ascent value from the top of the text frame, but it’s not that simple – especially in fonts where hhea.ascent + |hhea.descent| != 1000.

Here is my test data (for simplicity’s sake, font size = UPM = 1000):

    # SourceSansPro-Bold
    # head.yMax: 1009
    # hhea.ascent: 984
    # hhea.descent: -273
    # hhea.lineGap: 0
    # baseline is 855 below top of text frame

    # SourceSerifPro-Light
    # head.yMax: 976
    # hhea.ascent: 1036
    # hhea.descent: -335
    # hhea.lineGap: 0
    # baseline is 850 below top of text frame

    # MyriadPro-Light
    # head.yMax: 935
    # hhea.ascent: 750
    # hhea.descent: -250
    # hhea.lineGap: 200
    # baseline is 750 below top of text frame

This may have been solved by @petrvanblokland – I assume pageBot can deal with baselines?
@frankrolf
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This may or may not be related with #52

@frankrolf
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frankrolf commented May 23, 2017 •
edited

I stumbled upon textBoxBaselines, but something seems to be broken:

box = (0, 0, 1000, 1000)
print textBoxBaselines('whatever', box)

Traceback (most recent call last):
  File "<untitled>", line 8, in <module>
  File "drawBot/drawBotDrawingTools.pyc", line 1716, in textBoxBaselines
AttributeError: 'DrawBotDrawingTool' object has no attribute '_getPathForFrameSetter'

@petrvanblokland
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petrvanblokland commented May 23, 2017 via email

@frankrolf
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Thanks Petr – the sample was filtered out (by Github I assume), but maybe you can email it privately? (or post here?)

@petrvanblokland
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Here it is.
testFSBaselineCalculation2.py.zip

@frankrolf
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frankrolf commented May 24, 2017 •
edited

Unfortunately that trick only works for a very small subset of fonts, Times among them.

import random as rnd

height = width = 1000
t = "hello world "
point_size = 100
line_height = point_size * 1.2
y_value = 500

font_names = ['Times']
font_names.extend(rnd.sample(installedFonts(), 9))

for font_name in font_names:
    newPage(width, height)

    fs_font_name_label = FormattedString(
        font_name,
        font=font_name,
        fontSize=point_size/2,
        lineHeight=line_height
    )

    fs_single = FormattedString(
        t,
        font=font_name,
        fontSize=point_size,
        lineHeight=line_height
    )

    font(font_name)
    fontSize(point_size)
    lineHeight(line_height)

    print font_name
    print fs_single.fontLineHeight()
    print fs_single.fontDescender()
    print

    text(fs_single, (0, y_value))

    r = (100, 0, 1000, y_value + fontLineHeight() + fontDescender())
    label_rect = (100, height-200, width-200, 200)

    fs_multiline = FormattedString(
        t * 10,
        font=font_name,
    fontSize=point_size)

    textBox(fs_font_name_label, label_rect)
    textBox(fs_multiline, r)

    strokeWidth(.2)
    stroke(0, 0 ,1)

    line((0, y_value), (1000, y_value))

    stroke(1, 0, 0)
    fill(None)
    rect(*r)

baseline.pdf

@petrvanblokland
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petrvanblokland commented May 24, 2017 via email

@typemytype
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DrawBot does not do any calculations to retrieve the position of the first line. That's all CoreText. DrawBot just draws glyph runs at a specific position.

This document should describe how CoreText is using the different 'typographical' terms: https://developer.apple.com/library/content/documentation/StringsTextFonts/Conceptual/TextAndWebiPhoneOS/TypoFeatures/TextSystemFeatures.html

the textBoxBaselines bug should be already solved. What version did you test in?

@typemytype
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but you can calculate the pos super precise :)

(but textBoxBaselines has to work :)

import random as rnd

point_size = 100
line_height = 50

t = "Hello World"
x, y = 68, 672

font_names = ['Times']
font_names.extend(rnd.sample(installedFonts(), 9))

boxWidth, boxHeight = 800, 500

for font_name in font_names:
    newPage(1000, 1000)
    
    single = FormattedString()
    single.font(font_name, point_size)
    single.lineHeight(line_height)
    single += font_name
    text(single, (x, y))
    
    
    multi = FormattedString()
    multi.font(font_name, point_size)
    multi.lineHeight(line_height)
    multi += t * 100
    
    box = (x+ 100, 
        y-boxHeight, 
        boxWidth, 
        boxHeight)
    
    # get the pos of the first line
    startX, startY = textBoxBaselines(multi, box)[0]
    # move the box back towards that first line
    save()
    translate(0, y-startY)
    textBox(multi, box)
    restore()
    
    save()
    stroke(1, 0, 0)
    fill(None)
    rect(*box)
    restore()

@frankrolf
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Thank you Frederik. So what’s needed to make textBoxBaselines work?

Traceback (most recent call last):
  File "<untitled>", line 35, in <module>
  File "drawBot/drawBotDrawingTools.pyc", line 1716, in textBoxBaselines
AttributeError: 'DrawBotDrawingTool' object has no attribute '_getPathForFrameSetter'

@typemytype
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Maybe I have to push a new update... will check

@frankrolf
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Does not work in 3.97 yet.
This reminder comment was encouraged by Frederik sitting next to me.

@typemytype
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this should work in the latest versions...

@justvanrossum
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@frankrolf, can this be closed?

@frankrolf
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This can indeed be closed.
Thanks for making textBoxBaselines work!

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@petrvanblokland @typemytype @frankrolf @justvanrossum