Add a Paintbrush like example

A widget where user can draw on a canvas with different color.
It is possible to save and load the canvas into a PNG file.
This example teaches the user how to use QPainter outside the paintEvent
using a QPixmap.

Pick-to: 6.0
Task-number: PYSIDE-841
Change-Id: I8bbab68193894f4f5a6e101fa23fc65e6cb30864
Reviewed-by: Cristian Maureira-Fredes <cristian.maureira-fredes@qt.io>

2 files changed, 241 insertions, 0 deletions

diff --git a/examples/widgets/painting/painter/painter.py b/examples/widgets/painting/painter/painter.py
new file mode 100644
index 000000000..c9e2e4a10
--- /dev/null
+++ b/examples/widgets/painting/painter/painter.py
@@ -0,0 +1,238 @@
+#############################################################################
+##
+## Copyright (C) 2021 The Qt Company Ltd.
+## Contact: https://www.qt.io/licensing/
+##
+## This file is part of the Qt for Python examples of the Qt Toolkit.
+##
+## $QT_BEGIN_LICENSE:BSD$
+## You may use this file under the terms of the BSD license as follows:
+##
+## "Redistribution and use in source and binary forms, with or without
+## modification, are permitted provided that the following conditions are
+## met:
+##   * Redistributions of source code must retain the above copyright
+##     notice, this list of conditions and the following disclaimer.
+##   * Redistributions in binary form must reproduce the above copyright
+##     notice, this list of conditions and the following disclaimer in
+##     the documentation and/or other materials provided with the
+##     distribution.
+##   * Neither the name of The Qt Company Ltd nor the names of its
+##     contributors may be used to endorse or promote products derived
+##     from this software without specific prior written permission.
+##
+##
+## THIS SOFTWARE IS PROVIDED BY THE COPYRIGHT HOLDERS AND CONTRIBUTORS
+## "AS IS" AND ANY EXPRESS OR IMPLIED WARRANTIES, INCLUDING, BUT NOT
+## LIMITED TO, THE IMPLIED WARRANTIES OF MERCHANTABILITY AND FITNESS FOR
+## A PARTICULAR PURPOSE ARE DISCLAIMED. IN NO EVENT SHALL THE COPYRIGHT
+## OWNER OR CONTRIBUTORS BE LIABLE FOR ANY DIRECT, INDIRECT, INCIDENTAL,
+## SPECIAL, EXEMPLARY, OR CONSEQUENTIAL DAMAGES (INCLUDING, BUT NOT
+## LIMITED TO, PROCUREMENT OF SUBSTITUTE GOODS OR SERVICES; LOSS OF USE,
+## DATA, OR PROFITS; OR BUSINESS INTERRUPTION) HOWEVER CAUSED AND ON ANY
+## THEORY OF LIABILITY, WHETHER IN CONTRACT, STRICT LIABILITY, OR TORT
+## (INCLUDING NEGLIGENCE OR OTHERWISE) ARISING IN ANY WAY OUT OF THE USE
+## OF THIS SOFTWARE, EVEN IF ADVISED OF THE POSSIBILITY OF SUCH DAMAGE."
+##
+## $QT_END_LICENSE$
+##
+#############################################################################
+
+from PySide6.QtWidgets import (
+    QWidget,
+    QMainWindow,
+    QApplication,
+    QFileDialog,
+    QStyle,
+    QColorDialog,
+)
+from PySide6.QtCore import QPoint, Qt, QDir, Slot, QStandardPaths
+from PySide6.QtGui import (
+    QMouseEvent,
+    QPaintEvent,
+    QPen,
+    QAction,
+    QPainter,
+    QColor,
+    QPixmap,
+    QIcon,
+    QKeySequence,
+)
+import sys
+
+
+class PainterWidget(QWidget):
+    """A widget where user can draw with their mouse
+
+    The user draws on a QPixmap which is itself paint from paintEvent()
+
+    """
+
+    def __init__(self, parent=None):
+        super().__init__(parent)
+
+        self.setFixedSize(680, 480)
+        self.pixmap = QPixmap(self.size())
+        self.pixmap.fill(Qt.white)
+
+        self.previous_pos = None
+        self.painter = QPainter()
+        self.pen = QPen()
+        self.pen.setWidth(10)
+        self.pen.setCapStyle(Qt.RoundCap)
+        self.pen.setJoinStyle(Qt.RoundJoin)
+
+    def paintEvent(self, event: QPaintEvent):
+        """Override method from QWidget
+
+        Paint the Pixmap into the widget
+
+        """
+        painter = QPainter()
+        painter.begin(self)
+        painter.drawPixmap(0, 0, self.pixmap)
+        painter.end()
+
+    def mousePressEvent(self, event: QMouseEvent):
+        """Override from QWidget
+
+        Called when user clicks on the mouse
+
+        """
+        self.previous_pos = event.position().toPoint()
+        QWidget.mousePressEvent(self, event)
+
+    def mouseMoveEvent(self, event: QMouseEvent):
+        """Override method from QWidget
+
+        Called when user moves and clicks on the mouse
+
+        """
+        current_pos = event.position().toPoint()
+        self.painter.begin(self.pixmap)
+        self.painter.setRenderHints(QPainter.Antialiasing, True)
+        self.painter.setPen(self.pen)
+        self.painter.drawLine(self.previous_pos, current_pos)
+        self.painter.end()
+
+        self.previous_pos = current_pos
+        self.update()
+
+        QWidget.mouseMoveEvent(self, event)
+
+    def mouseReleaseEvent(self, event: QMouseEvent):
+        """Override method from QWidget
+
+        Called when user releases the mouse
+
+        """
+        self.previous_pos = None
+        QWidget.mouseReleaseEvent(self, event)
+
+    def save(self, filename: str):
+        """ save pixmap to filename """
+        self.pixmap.save(filename)
+
+    def load(self, filename: str):
+        """ load pixmap from filename """
+        self.pixmap.load(filename)
+        self.pixmap = self.pixmap.scaled(self.size(), Qt.KeepAspectRatio)
+        self.update()
+
+    def clear(self):
+        """ Clear the pixmap """
+        self.pixmap.fill(Qt.white)
+        self.update()
+
+
+class MainWindow(QMainWindow):
+    """An Application example to draw using a pen """
+
+    def __init__(self, parent=None):
+        QMainWindow.__init__(self, parent)
+
+        self.painter_widget = PainterWidget()
+        self.bar = self.addToolBar("Menu")
+        self.bar.setToolButtonStyle(Qt.ToolButtonTextBesideIcon)
+        self._save_action = self.bar.addAction(
+            qApp.style().standardIcon(QStyle.SP_DialogSaveButton), "Save", self.on_save
+        )
+        self._save_action.setShortcut(QKeySequence.Save)
+        self._open_action = self.bar.addAction(
+            qApp.style().standardIcon(QStyle.SP_DialogOpenButton), "Open", self.on_open
+        )
+        self._open_action.setShortcut(QKeySequence.Open)
+        self.bar.addAction(
+            qApp.style().standardIcon(QStyle.SP_DialogResetButton),
+            "Clear",
+            self.painter_widget.clear,
+        )
+        self.bar.addSeparator()
+
+        self.color_action = QAction(self)
+        self.color_action.triggered.connect(self.on_color_clicked)
+        self.bar.addAction(self.color_action)
+
+        self.setCentralWidget(self.painter_widget)
+
+        self.set_color(Qt.black)
+
+        self.mime_type_filters = ["image/png", "image/jpeg"]
+
+    @Slot()
+    def on_save(self):
+
+        dialog = QFileDialog(self, "Save File")
+        dialog.setMimeTypeFilters(self.mime_type_filters)
+        dialog.setFileMode(QFileDialog.AnyFile)
+        dialog.setAcceptMode(QFileDialog.AcceptSave)
+        dialog.setDefaultSuffix("png")
+        dialog.setDirectory(
+            QStandardPaths.writableLocation(QStandardPaths.PicturesLocation)
+        )
+
+        if dialog.exec_() == QFileDialog.Accepted:
+            if dialog.selectedFiles():
+                self.painter_widget.save(dialog.selectedFiles()[0])
+
+    @Slot()
+    def on_open(self):
+
+        dialog = QFileDialog(self, "Save File")
+        dialog.setMimeTypeFilters(self.mime_type_filters)
+        dialog.setFileMode(QFileDialog.ExistingFile)
+        dialog.setAcceptMode(QFileDialog.AcceptOpen)
+        dialog.setDefaultSuffix("png")
+        dialog.setDirectory(
+            QStandardPaths.writableLocation(QStandardPaths.PicturesLocation)
+        )
+
+        if dialog.exec_() == QFileDialog.Accepted:
+            if dialog.selectedFiles():
+                self.painter_widget.load(dialog.selectedFiles()[0])
+
+    @Slot()
+    def on_color_clicked(self):
+
+        color = QColorDialog.getColor(Qt.black, self)
+        if color:
+            self.set_color(color)
+
+    def set_color(self, color: QColor = Qt.black):
+
+        # Create color icon
+        pix_icon = QPixmap(32, 32)
+        pix_icon.fill(color)
+
+        self.color_action.setIcon(QIcon(pix_icon))
+        self.painter_widget.pen.setColor(color)
+        self.color_action.setText(QColor(color).name())
+
+
+if __name__ == "__main__":
+
+    app = QApplication(sys.argv)
+
+    w = MainWindow()
+    w.show()
+    sys.exit(app.exec_())
diff --git a/examples/widgets/painting/painter/painter.pyproject b/examples/widgets/painting/painter/painter.pyproject
new file mode 100644
index 000000000..f47831696
--- /dev/null
+++ b/examples/widgets/painting/painter/painter.pyproject
@@ -0,0 +1,3 @@
+{
+    "files": ["painter.py"]
+}