Qt syntax

If your hands already know Qt, blenderui.qtsyntax lets them keep typing: QApplication, QWidget, QVBoxLayout, clicked.connect(...). BUI runs that code on its own C runtime and draws it with Blender’s widgets. Neither Qt nor PySide is needed.

A first example

import sys
from blenderui.qtsyntax import (QApplication, QWidget, QVBoxLayout, QSlider,
                                QProgressBar, QPushButton, Qt)

app = QApplication(sys.argv)
window = QWidget()
window.setWindowTitle("Hello, Qt syntax")

layout = QVBoxLayout(window)
slider = QSlider(Qt.Horizontal)
slider.setRange(0, 100)
bar = QProgressBar()
slider.valueChanged.connect(bar.setValue)     # signals connect to any callable
quit_button = QPushButton("Quit")
quit_button.clicked.connect(app.quit)
layout.addWidget(slider)
layout.addWidget(bar)
layout.addWidget(quit_button)

window.resize(320, 140)
window.show()
sys.exit(app.exec())

The only line that differs from PySide is the import. For a step-by-step build of a fuller form, follow the Qt tutorial.

How it maps

There’s no Qt underneath. Each piece of Qt maps onto something in BUI:

Supported classes

The member-by-member list is in SYNTAX_COVERAGE.md.

Signals

Signals work as in Qt: declare them on a class, connect any callable, emit to call them.

from blenderui.qtsyntax import QWidget, Signal

class Thermostat(QWidget):
    changed = Signal(float)           # pyqtSignal and Signal_ are the same thing

t = Thermostat()
t.changed.connect(lambda v: print("now", v))
t.changed.connect(print)
t.changed.emit(21.5)

• Slots can take fewer arguments than the signal sends: QPushButton.clicked sends a bool, but a slot with no parameters is called with none.
• disconnect(slot) removes one slot; disconnect() removes them all.
• Programmatic changes go through the kit, so in our testing a setValue made before the window opens doesn’t emit valueChanged. Set dependent widgets yourself at startup, or make the change after show().

Layouts

Layouts behave like Qt’s, including the parts people rely on without thinking:

• addWidget(widget, stretch) and addStretch() share spare space by stretch factor.
• Spacing goes between items only, and margins apply to top-level layouts only.
• Line edits, sliders, combo boxes and progress bars expand horizontally; text edits, lists, trees, tabs and custom-painted widgets expand vertically.
• QGridLayout.addWidget(w, row, column, rowspan, colspan, alignment) and setRowStretch / setColumnStretch work.

Custom painting

Override paintEvent and draw with QPainter. On BUI, your drawing is recorded into a display list that BUI redraws for you; call update() when your data changes.

import sys
from blenderui.qtsyntax import (QApplication, QWidget, QVBoxLayout, QLabel,
                                QPainter, QColor, QPen)

class Gauge(QWidget):
    def __init__(self):
        super().__init__()
        self.value = 0.6

    def paintEvent(self, event):
        p = QPainter(self)
        p.setBrush(QColor("#282828"))
        p.drawRoundedRect(0, 0, self.width(), 24, 6, 6)
        p.setBrush(QColor("#4772b3"))
        p.drawRoundedRect(0, 0, int(self.width() * self.value), 24, 6, 6)
        p.setPen(QPen(QColor("white")))
        p.drawText(8, 17, "%d%%" % (self.value * 100))
        p.end()

    def mousePressEvent(self, e):
        self.value = e.x() / max(1, self.width())
        self.update()                  # repaint

app = QApplication(sys.argv)
window = QWidget()
window.setWindowTitle("Gauge")
layout = QVBoxLayout(window)
layout.addWidget(QLabel("Click the gauge:"))
layout.addWidget(Gauge())
window.resize(300, 120)
window.show()
sys.exit(app.exec())

QPainter supports fillRect, drawRect, drawRoundedRect, drawEllipse, drawLine, drawPolyline, drawPolygon, drawPoint, drawArc, drawPie, drawText and drawPixmap, plus setPen, setBrush, setFont, setOpacity, translate, save and restore.

Style sheets

setStyleSheet understands three things: color, background (or background-color) on containers, and font-weight: bold. Everything else is Blender’s theme. Qt style sheet selectors, pseudo-states and QPalette aren’t supported.

What’s missing

Being upfront, so you don’t find out the hard way:

• Model/view: QAbstractItemModel, QListView, QTreeView, QTableView and delegates. Use the *Widget classes instead.
• Classes: QSplitter, QDockWidget, QToolBar, QStackedWidget (as a real class), QToolBox, QDateEdit and friends, QCalendarWidget, QGraphicsScene, OpenGL widgets.
• Most of QWidget’s surface: focus-policy details, setWindowFlags, geometry helpers, grab.
• Infrastructure: QSettings, QThread, QClipboard, drag and drop, QShortcut, rich text.
• Drawn dialogs: QMessageBox and QInputDialog aren’t drawn yet. QMessageBox.information, warning, critical and about return Ok at once, and question returns Yes at once, without showing anything.

Next steps