How to force screen-snip size ratio. PyQt5

Question

I want to modify Screen-Snip code from GitHub/harupy/snipping-tool so that every screen-snip has a ratio of 3 x 2. (I will save as 600 x 400 px image later)

I'm not sure how to modify self.end dynamically so that the user clicks and drags with a 3 x 2 ratio. The mouse position will define the x coordinate, and the y coordinate will be int(x * 2/3)

Any suggestions on how to do this? I promise I've been researching this, and I just can't seem to "crack the code" of modifying only the y coordinate of self.end

Here is the code:

import sys
import PyQt5
from PyQt5 import QtWidgets, QtCore, QtGui
import tkinter as tk
from PIL import ImageGrab
import numpy as np
import cv2 # package is officially called opencv-python


class MyWidget(QtWidgets.QWidget):
    def __init__(self):
        super().__init__()
        root = tk.Tk()
        screen_width = root.winfo_screenwidth()
        screen_height = root.winfo_screenheight()
        self.setGeometry(0, 0, screen_width, screen_height)
        self.setWindowTitle(' ')
        self.begin = QtCore.QPoint()
        self.end = QtCore.QPoint()
        self.setWindowOpacity(0.3)
        QtWidgets.QApplication.setOverrideCursor(
            QtGui.QCursor(QtCore.Qt.CrossCursor)
        )
        self.setWindowFlags(QtCore.Qt.FramelessWindowHint)
        print('Capture the screen...')
        self.show()

    def paintEvent(self, event):
        qp = QtGui.QPainter(self)
        qp.setPen(QtGui.QPen(QtGui.QColor('black'), 3))
        qp.setBrush(QtGui.QColor(128, 128, 255, 128))
        qp.drawRect(QtCore.QRect(self.begin, self.end)) ##### This seems like the place I should modify. #########

    def mousePressEvent(self, event):
        self.begin = event.pos()
        self.end = self.begin
        self.update()

    def mouseMoveEvent(self, event):
        self.end = event.pos()
        self.update()

    def mouseReleaseEvent(self, event):
        self.close()

        x1 = min(self.begin.x(), self.end.x())
        y1 = min(self.begin.y(), self.end.y())
        x2 = max(self.begin.x(), self.end.x())
        y2 = max(self.begin.y(), self.end.y())

        img = ImageGrab.grab(bbox=(x1, y1, x2, y2))
        img.save('capture.png')
        img = cv2.cvtColor(np.array(img), cv2.COLOR_BGR2RGB)

        cv2.imshow('Captured Image', img)
        cv2.waitKey(0)
        cv2.destroyAllWindows()


if __name__ == '__main__':
    app = QtWidgets.QApplication(sys.argv)
    window = MyWidget()
    window.show()
    app.aboutToQuit.connect(app.deleteLater)
    sys.exit(app.exec_())

musicamante · Accepted Answer · 2020-07-31T16:41:46.657

You don't need to "change the y coordinate", you just need to use the correct arguments to create the rectangle. There are various ways to initialize a QRect, you are using the two points, another one (and more common) is to use the coordinates of the origin and the size of the rectangle.

Once you know the width, you can compute the height, and make it negative if the y of the end point is above the begin.

Note that in this way you could get a "negative" rectangle (negative width, with the "right" edge actually at the left, the same for the height/bottom), so it's usually better to use normalized, which also allows you to get the correct coordinates of the rectangle for screen grabbing.

class MyWidget(QtWidgets.QWidget):
    # ...

    def getRect(self):
        # a commodity function that always return a correctly sized
        # rectangle, with normalized coordinates
        width = self.end.x() - self.begin.x()
        height = abs(width * 2 / 3)
        if self.end.y() < self.begin.y():
            height *= -1
        return QtCore.QRect(self.begin.x(), self.begin.y(), 
            width, height).normalized()

    def paintEvent(self, event):
        qp = QtGui.QPainter(self)
        qp.setPen(QtGui.QPen(QtGui.QColor('black'), 3))
        qp.setBrush(QtGui.QColor(128, 128, 255, 128))
        qp.drawRect(self.getRect())

    def mouseReleaseEvent(self, event):
        self.close()

        rect = self.getRect()
        img = ImageGrab.grab(bbox=(
            rect.topLeft().x(), 
            rect.topLeft().y(), 
            rect.bottomRight().x(), 
            rect.bottomRight().y()
        ))

        # ...

I suggest you to use a delayed setGeometry as in some systems (specifically Linux), the "final" geometry is actually applied only as soon as the window is correctly mapped from the window manager, especially if the window manager tends to apply a geometry on its own when the window is shown the first time. For example, I have two screens, and your window got "centered" on my main screen, making it shifted by half width of the other screen. Also consider that importing Tk just for the screen size doesn't make much sense, since Qt already provides all necessary tools.

You can use something like that:

class MyWidget(QtWidgets.QWidget):
    # ...

    def showEvent(self, event):
        if not event.spontaneous():
            # delay the geometry on the "next" cycle of the Qt event loop;
            # this should take care of positioning issues for systems that
            # try to move newly created windows on their own
            QtCore.QTimer.singleShot(0, self.resetPos)

    def resetPos(self):
        rect = QtCore.QRect()
        # create a rectangle that is the sum of the geometries of all available
        # screens; the |= operator acts as `rect = rect.united(screen.geometry())`
        for screen in QtWidgets.QApplication.screens():
            rect |= screen.geometry()
        self.setGeometry(rect)

How to force screen-snip size ratio. PyQt5

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