`cv::setWindowProperty`

High-level GUI
#include <opencv2/highgui.hpp>

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1. `setWindowProperty()`

void cv::setWindowProperty(const String &winname, int prop_id, double prop_value) - C++
None = cv.setWindowProperty(winname, prop_id, prop_value) - Python

Changes parameters of a window dynamically.
动态更改窗口的参数。

The function setWindowProperty enables changing properties of a window.
函数 setWindowProperty 启用更改窗口的属性。

1.1 Parameters

winname - Name of the window.
prop_id - Window property to edit. The supported operation flags are: (cv::WindowPropertyFlags)
prop_value - New value of the window property. The supported flags are: (cv::WindowFlags)

2. WindowPropertyFlags

enum cv::WindowPropertyFlags

Flags for cv::setWindowProperty / cv::getWindowProperty.

2.1 Enumerator

C++: WND_PROP_FULLSCREEN
Python: cv.WND_PROP_FULLSCREEN
fullscreen property (can be WINDOW_NORMAL or WINDOW_FULLSCREEN).

C++: WND_PROP_AUTOSIZE
Python: cv.WND_PROP_AUTOSIZE
autosize property (can be WINDOW_NORMAL or WINDOW_AUTOSIZE).

C++: WND_PROP_ASPECT_RATIO
Python: cv.WND_PROP_ASPECT_RATIO
window’s aspect ration (can be set to WINDOW_FREERATIO or WINDOW_KEEPRATIO).

C++: WND_PROP_OPENGL
Python: cv.WND_PROP_OPENGL
opengl support.

C++: WND_PROP_VISIBLE
Python: cv.WND_PROP_VISIBLE
checks whether the window exists and is visible
检查窗口是否存在并可见

C++: WND_PROP_TOPMOST
Python: cv.WND_PROP_TOPMOST
property to toggle normal window being topmost or not
属性以切换正常窗口是否位于最顶部

3. WindowFlags

enum cv::WindowFlags

Flags for cv::namedWindow.

3.1 Enumerator

C++: WINDOW_NORMAL
Python: cv.WINDOW_NORMAL
the user can resize the window (no constraint) / also use to switch a fullscreen window to a normal size.
用户可以调整窗口大小（无限制），也可以将全屏窗口切换为正常大小。

C++: WINDOW_AUTOSIZE
Python: cv.WINDOW_AUTOSIZE
the user cannot resize the window, the size is constrainted by the image displayed.
用户无法调整窗口大小，该大小受所显示图像的限制。

C++: WINDOW_OPENGL
Python: cv.WINDOW_OPENGL
window with opengl support.

C++: WINDOW_FULLSCREEN
Python: cv.WINDOW_FULLSCREEN
change the window to fullscreen.

C++: WINDOW_FREERATIO
Python: cv.WINDOW_FREERATIO
the image expends as much as it can (no ratio constraint).

C++: WINDOW_KEEPRATIO
Python: cv.WINDOW_KEEPRATIO
the ratio of the image is respected.

C++: `WINDOW_GUI_EXPANDED
Python: cv.WINDOW_GUI_EXPANDED
status bar and tool bar

C++: `WINDOW_GUI_NORMAL
Python: cv.WINDOW_GUI_NORMAL
old fashious way

4. Example

//============================================================================
// Name        : X11/Xlib.h
// Author      : Yongqiang Cheng
// Version     : Feb 22, 2020
// Copyright   : Copyright (c) 2019 Yongqiang Cheng
// Description : Hello World in C++, Ansi-style
//============================================================================

#include <opencv2/core.hpp>
#include <opencv2/videoio.hpp>
#include <opencv2/highgui.hpp>

#include <iostream>
#include <stdio.h>

using namespace cv;
using namespace std;

int main(int, char**)
{
	Mat frame;
	const char MAIN_WINDOW_NAME[] = "yongqiang";
	const bool SCREEN_FULL = true;

	//--- INITIALIZE VIDEOCAPTURE
	VideoCapture cap;
	// open the default camera using default API
	// cap.open(0);
	// OR advance usage: select any API backend
	int deviceID = 0;             // 0 = open default camera
	int apiID = cv::CAP_ANY;      // 0 = autodetect default API
	// open selected camera using selected API
	cap.open(deviceID + apiID);
	// check if we succeeded
	if (!cap.isOpened())
	{
		cerr << "ERROR! Unable to open camera\n";
		return -1;
	}

	namedWindow(MAIN_WINDOW_NAME, WINDOW_NORMAL);
	setWindowProperty(MAIN_WINDOW_NAME, WND_PROP_FULLSCREEN, WINDOW_FULLSCREEN);

	//--- GRAB AND WRITE LOOP
	cout << "Start grabbing" << endl << "Press any key to terminate" << endl;
	for (;;)
	{
		// wait for a new frame from camera and store it into 'frame'
		cap.read(frame);
		// check if we succeeded
		if (frame.empty())
		{
			cerr << "ERROR! blank frame grabbed\n";
			break;
		}

		// show live and wait for a key with timeout long enough to show images
		imshow(MAIN_WINDOW_NAME, frame);
		if (waitKey(5) >= 0)
		{
			break;
		}
	}

	// the camera will be deinitialized automatically in VideoCapture destructor
	return 0;
}

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