c++ - 我想让 setmousecallback 函数在仍然按下鼠标左键时连续传递坐标

Question

我的代码工作正常，但当鼠标左键仍被按下时，它不会连续传递坐标。它确实在鼠标移动时传递坐标。

抱歉，我没有添加 mouse_callback 函数，我现在添加了它。任何帮助都会有所帮助。代码:

#include <stdio.h>
#include <opencv2/opencv.hpp>
#include <opencv2/highgui.hpp>
#include <opencv2/imgproc.hpp>
#include <iostream>

using namespace cv;
using namespace std;

Point pt(-1, -1);
bool newCoords = false;
void mouse_callback(int  event, int  x, int  y, int  flag, void *param)
{
if (event == EVENT_LBUTTONDOWN)
{
    pt.x = x;
    pt.y = y;
    newCoords = true;
}
else if (flag == EVENT_FLAG_LBUTTON && event == EVENT_MOUSEMOVE) {
    pt.x = x;
    pt.y = y;
    newCoords = true;
}
}

int main(int argc, char** argv)
{
    String WindowName = "Original Feed";
    namedWindow(WindowName, CV_WINDOW_AUTOSIZE);
    Mat oriImg;
    int Frame_Width = 720;
    int Frame_Height = 540;

    VideoCapture cap(0);
    setMouseCallback(WindowName, mouse_callback);

    cap.set(CV_CAP_PROP_FRAME_WIDTH, Frame_Width);
    cap.set(CV_CAP_PROP_FRAME_HEIGHT, Frame_Height);

    while (waitKey(30) != 27) {
        cap.read(oriImg);
        if (pt.x != -1 && pt.y != -1)
        {
            circle(oriImg, pt, 3, Scalar(0, 0, 255));

            if (newCoords)
            {
                std::cout << "Clicked coordinates: " << pt << std::endl;
                newCoords = false;
            }
        }

        imshow(WindowName, oriImg);
    }
    return 0;
}

Answer 1

只要 OS/GUI 生成鼠标事件，就会调用回调。只要鼠标的状态(按钮、滚轮、位置等)发生变化，就会生成此类事件——如果没有任何变化，则您已经知道(可以知道)当前状态。

如果您想在多次迭代中以某种方式响应鼠标的稳定状态(例如，在静止时按住按钮)，您必须自己处理。

---

我对你的问题的理解是这样的:只要按住左键，在显示的每一帧光标最近的位置画一个圆。

由于我们以合适的帧速率运行，我们可以让事情变得简单，并且仅根据前一帧的点击/位置信息更新当前帧。用户将无法观察到这种轻微的延迟。

仅供后代使用:图像正在显示，鼠标回调仅在 cv::waitKey 函数运行时调用。

---

下面列举了我们在每次迭代中可能遇到的情况，以及我们应该在下面的框架中如何应对:

1. waitKey 的入口和导出处未持有 LMB
   • LMB 从未被释放(因此从未按下)-> 无事可做
   • LMB 至少被按住和释放一次(因此被按下了很多次)-> 在最后一次按下的位置画圆
2. LMB 未在入口处保留，但在 waitKey 的导出处保留
   • 按住 LMB -> 在最后报告的鼠标位置画圆
3. LMB 在入口处持有，但在 waitKey 导出处未持有
   • LMB 至少被按住和释放一次(并且少按一次)-> 在最后一次按下的位置画圆
4. LMB 在 waitKey 的入口和导出处举行
   • 按住 LMB -> 在最后报告的鼠标位置画圆

基于此，我们需要跟踪:

• 最后一次按下或释放 LMB 的位置。
• LMB 当前是否被按住
• LMB 是否在上一次迭代中被释放(即它被按住，即使它不再是)

我们可以使用 struct 来保存此信息(由于用户数据参数，我们让回调使用它):

struct mouse_state
{
    mouse_state()
        : position(-1, -1)
        , left_button_held(false)
        , left_button_clicked(false)
    {}

    void new_iteration()
    {
        left_button_clicked = false;
    }

    cv::Point2i position; // Last position where the LMB was down
    bool left_button_held; // Is the LMB down right now?
    bool left_button_clicked; // Was the LMB down in the last iteration?
};

鼠标回调将负责更新上述struct。

• 当用户按下 LMB 时，记录位置并按住设置按钮
• 当用户释放 LMB 时，记录位置，点击设置按钮，不按住设置按钮
• 当鼠标移动并按住 LMB 时，记录位置

带有一些原始调试跟踪的回调实现示例如下所示:

void mouse_callback(int event, int x, int y, int flag, void* param)
{
    mouse_state* state(static_cast<mouse_state*>(param));

    if (event == cv::EVENT_LBUTTONDOWN) {
        std::cout << "LMB down @ (" << x << "," << y << ")\n";
        state->position = cv::Point2i(x, y);
        state->left_button_held = true;
    } else if (event == cv::EVENT_LBUTTONUP) {
        std::cout << "LMB up @(" << x << "," << y << ")\n";
        state->position = cv::Point2i(x, y);
        state->left_button_held = false;
        state->left_button_clicked = true;
    } else if ((flag == cv::EVENT_FLAG_LBUTTON) && (event == cv::EVENT_MOUSEMOVE)) {
        std::cout << "LMB held, mouse moved to (" << x << "," << y << ")\n";
        state->position = cv::Point2i(x, y);
    }
}

然后可以通过以下方式注册回调:

mouse_state ms;
cv::setMouseCallback(WINDOW_NAME, mouse_callback, &ms);

处理循环将非常简单:

1. 读取新帧，失败退出循环
2. 检查鼠标的最后状态。如果按住或单击 LMB，则在记录的位置画圈。
3. 重置每次迭代鼠标状态标志
4. 显示图片，更新鼠标状态信息

这可能如下所示:

for (;;) {
    // We can have `image` here, since `cap.read` always gives us
    // a reference to its internal buffer
    cv::Mat image;
    if (!cap.read(image)) {
        std::cerr << "Failed to read image, exiting...\n";
        break; // Failed to read image, nothing else to do
    }

    if (ms.left_button_clicked || ms.left_button_held) {
        std::cout << "Current position: " << ms.position << "\n";
        cv::circle(image, ms.position, 3, cv::Scalar(0, 0, 255));
        cv::circle(image, ms.position, 10, cv::Scalar(0, 0, 255), 2);
    }

    ms.new_iteration();

    cv::imshow(WINDOW_NAME, image);
    if (cv::waitKey(30) == 27) {
        std::cout << "Esc pressed, exiting...\n";
        break;
    }
}

---

示例程序

#include <opencv2/opencv.hpp>
#include <iostream>

struct mouse_state
{
    mouse_state()
        : position(-1, -1)
        , left_button_held(false)
        , left_button_clicked(false)
    {}

    void new_iteration()
    {
        left_button_clicked = false;
    }

    cv::Point2i position; // Last position where the LMB was down
    bool left_button_held; // Is the LMB down right now?
    bool left_button_clicked; // Was the LMB down in the last iteration?
};

void mouse_callback(int event, int x, int y, int flag, void* param)
{
    mouse_state* state(static_cast<mouse_state*>(param));

    if (event == cv::EVENT_LBUTTONDOWN) {
        std::cout << "LMB down @ (" << x << "," << y << ")\n";
        state->position = cv::Point2i(x, y);
        state->left_button_held = true;
    } else if (event == cv::EVENT_LBUTTONUP) {
        std::cout << "LMB up @(" << x << "," << y << ")\n";
        state->position = cv::Point2i(x, y);
        state->left_button_held = false;
        state->left_button_clicked = true;
    } else if ((flag == cv::EVENT_FLAG_LBUTTON) && (event == cv::EVENT_MOUSEMOVE)) {
        std::cout << "LMB held, mouse moved to (" << x << "," << y << ")\n";
        state->position = cv::Point2i(x, y);
    }
}

int main(int argc, char** argv)
{
    cv::String const WINDOW_NAME("Original Feed");
    cv::namedWindow(WINDOW_NAME, CV_WINDOW_AUTOSIZE);

    mouse_state ms;
    cv::setMouseCallback(WINDOW_NAME, mouse_callback, &ms);

    int const FRAME_WIDTH(720);
    int const FRAME_HEIGHT(540);

    cv::VideoCapture cap(0);
    if (!cap.isOpened()) {
        std::cerr << "Unable to open camera, exiting...\n";
        return -1;
    }

    cap.set(CV_CAP_PROP_FRAME_WIDTH, FRAME_WIDTH);
    cap.set(CV_CAP_PROP_FRAME_HEIGHT, FRAME_HEIGHT);

    for (;;) {
        // We can have `image` here, since `cap.read` always gives us
        // a reference to its internal buffer
        cv::Mat image;
        if (!cap.read(image)) {
            std::cerr << "Failed to read image, exiting...\n";
            break; // Failed to read image, nothing else to do
        }

        if (ms.left_button_clicked || ms.left_button_held) {
            std::cout << "Current position: " << ms.position << "\n";
            cv::circle(image, ms.position, 3, cv::Scalar(0, 0, 255));
            cv::circle(image, ms.position, 10, cv::Scalar(0, 0, 255), 2);
        }

        ms.new_iteration();

        cv::imshow(WINDOW_NAME, image);
        if (cv::waitKey(30) == 27) {
            std::cout << "Esc pressed, exiting...\n";
            break;
        }
    }
    return 0;
}