feaLib.py

from fontTools.feaLib.error import FeatureLibError
import traceback

font = CurrentFont()

try:
    font.getRepresentation("defconQt.TTFont")
except FeatureLibError as e:
    traceback.print_exc()
    print(e.location)
else:
    print("C'est OKAY!")

layoutEngine.py

from defcon import LayoutEngine
from PyQt5.QtCore import pyqtSignal, Qt
from PyQt5.QtWidgets import QComboBox, QGridLayout, QGroupBox, QLineEdit, QRadioButton, QVBoxLayout, QWidget

class OpenTypeControls(QWidget):
    controlsChanged = pyqtSignal()

    def __init__(self, parent=None):
        super().__init__(parent)

        # writing direction
        ltrBox = QRadioButton("LTR", self)
        ltrBox.toggled.connect(self.controlsChanged)
        rtlBox = QRadioButton("RTL", self)
        directionGroupBox = QGroupBox("Writing direction", self)
        directionLayout = QVBoxLayout(self)
        directionLayout.addWidget(ltrBox)
        directionLayout.addWidget(rtlBox)
        directionGroupBox.setLayout(directionLayout)
        directionGroupBox.toggled.connect(self.controlsChanged)
        # script & language
        self.scriptBox = QComboBox(self)
        self.scriptBox.currentTextChanged.connect(self.controlsChanged)
        self.languageBox = QComboBox(self)
        self.languageBox.currentTextChanged.connect(self.controlsChanged)
        # feature list
        featGroupBox = QGroupBox("Feature list", self)
        featGroupBox.setFlat(True)
        self.groupBoxLayout = QVBoxLayout(self)
        featGroupBox.setLayout(self.groupBoxLayout)
        featGroupBox.toggled.connect(self.controlsChanged)
        
        layout = QVBoxLayout(self)
        layout.addWidget(directionGroupBox)
        layout.addWidget(self.scriptBox)
        layout.addWidget(self.languageBox)
        layout.addWidget(featGroupBox)
        self.setLayout(layout)
    
    def updateFromEngine(self, engine):
        # script & language
        currentText = self.scriptBox.currentText()
        self.scriptBox.clear()
        self.scriptBox.addItems(engine.getScriptList())
        self.scriptBox.setCurrentText(currentText)
        currentText = self.languageBox.currentText()
        self.languageBox.clear()
        self.languageBox.addItems(engine.getLanguageList())
        self.languageBox.setCurrentText(currentText)
        # destroy current checkboxes
        for checkBox in self.groupBoxLayout.children():
            checkBox.setParent(None)
        # populate features
        for feature in engine.getFeatureList():
            box = QCheckBox(feature, self.groupBoxLayout)
            box.setChecked(engine.getFeatureState(feature))
            #self.groupBoxLayout.addWidget(box)
        
        

class PreviewWindow(QWidget):
    def __init__(self, parent=None):
        super().__init__(parent, Qt.Window)
        self._font = CurrentFont()
        self._layoutEngine = LayoutEngine(self._font)

        otControls = OpenTypeControls(self)
        inputLine = QLineEdit(self)
        inputLine.textChanged.connect(self.updateView)
        canvas = QWidget(self)
        
        layout = QGridLayout()
        layout.addWidget(inputLine, 0, 0, 1, 2)
        layout.addWidget(otControls, 1, 0)
        layout.addWidget(canvas, 1, 1)
        self.setLayout(layout)
    
    def updateView(self, text):
        rec = self._layoutEngine.process(text)
        print(rec)

window = PreviewWindow()
window.show()

quad.py

from io import BytesIO
import traceback

font = CurrentFont()

try:
    ttf = font.getRepresentation("defconQt.QuadraticTTFont")
    stream = BytesIO()
    ttf.save(stream)
except:
    traceback.print_exc()

webView.py

from cu2qu.defcon import font_to_quadratic
from fontTools.feaLib.error import FeatureLibError
from io import BytesIO
from PyQt5.QtGui import QFontDatabase
try:
    # Chromium
    from PyQt5.QtWebEngineWidgets import QWebEngineView
except ImportError:
    # WebKit
    from PyQt5.QtWebKit import QWebView
    QWebEngineView = QWebView

class WebEngineFontView(QWebEngineView):
    def __init__(self, parent=None):
        super().__init__(parent)
        self._font = CurrentFont()
        self._font.addObserver(
            self, "_fontChanged", "Font.Changed")
        self._fontId = None
        self.updateFont()
    
    def closeEvent(self, event):
        self._font.removeObserver(self, "Font.Changed")
        event.accept()
    
    # drawbot, edited
    def _extractPSName(self, font):
        psName = font["name"].getName(6, 1, 0)
        if psName is None:
            psName = font["name"].getName(6, 3, 1)
        return psName
    
    def _fontChanged(self, notification):
        self.updateFont()
    
    def updateFont(self):
        font_to_quadratic(self._font)
        try:
            otf = self._font.getRepresentation(
                "defconQt.QuadraticTTFont")
        except FeatureLibError as e:
            traceback.print_exc()
            print(e.location)
            return
        stream = BytesIO()
        otf.save(stream)
        id = QFontDatabase.addApplicationFontFromData(
            stream.getvalue())
        if id == -1:
            return
        if self._fontId is not None:
            QFontDatabase.removeApplicationFont(
                self._fontId)
        psName = self._extractPSName(otf)
        if psName is None:
            return
        self._fontId = id
        self.updateHtml(psName)
    
    def updateHtml(self, psName):
        html = """
<head>
    <style>
        html {
            font-family: %s;
        }
    <style>
</head>
<body>
   Grumpy wizards make toxic brew for the evil Queen and Jack. A quick movement of the enemy will jeopardize six gunboats. The job of waxing linoleum frequently peeves chintzy kids. My girl wove six dozen plaid jackets before she quit. Twelve ziggurats quickly jumped a finch box.
</body>
        """ % psName
        self.setHtml(html)

webView = WebEngineFontView()
webView.show()