c++ - 清除绘制的矩形

Question

如何清除某个矩形？我在窗口中显示圆圈和每个圆圈 (TextOut) 内的文本。我尝试实现，使得在某个圆上按下鼠标左键时，该圆和文字消失，即清除该圆和文字所在的矩形。

#include <windows.h>; 
#include <ctime>
#include <cmath>

struct Cell {
    int x, y;
    struct rgb {
        int r, g, b,z;
    }
    mainColor,
    borderColor,
    circleColor,
    textColor,
    circleSize, 
    circleBorderColor;  
};

HWND hWnd;
HDC hdc;
HPALETTE hPal;
BOOL bForceBkgd;
COLORREF color;
HBRUSH brush;

const int rectSize = 90;
const int circleSize = 40;

int y = 0, x = 0, yCoord, xCoord;
char buf[50];

bool flag = 0;
Cell cells[7][7];
HINSTANCE hInst; //Дескриптор програми
LPCTSTR szWindowClass = "QWERTY";
LPCTSTR szTitle = "  ";
// Попередній опис функцій
ATOM MyRegisterClass(HINSTANCE hInstance);
BOOL InitInstance(HINSTANCE, int);
LRESULT CALLBACK WndProc(HWND, UINT, WPARAM, LPARAM);

bool isInCircle(int x, int y, int x0, int y0, int R) {
    if (pow((x - x0), 2) + pow((y - y0), 2) <= pow(R, 2)) {
        return true;
    }
    return false;
}

// main program
int APIENTRY WinMain(HINSTANCE hInstance, HINSTANCE hPrevInstance, LPSTR lpCmdLine, int nCmdShow)
{
    srand(time(NULL));

    MSG msg;
    // window class register
    MyRegisterClass(hInstance);
    // creating a program window
    if (!InitInstance(hInstance, nCmdShow))
    {
        return FALSE;
    }
    // messages processing cycle
    while (GetMessage(&msg, NULL, 0, 0))
    {
        TranslateMessage(&msg);
        DispatchMessage(&msg);
    }
    return msg.wParam;
}

ATOM MyRegisterClass(HINSTANCE hInstance)
{
    WNDCLASSEX wcex;
    wcex.cbSize = sizeof(WNDCLASSEX);
    wcex.style = CS_HREDRAW | CS_VREDRAW; 
    wcex.lpfnWndProc = (WNDPROC)WndProc; 
    wcex.cbClsExtra = 0;
    wcex.cbWndExtra = 0;
    wcex.hInstance = hInstance; 
    wcex.hIcon = LoadIcon(NULL, IDI_SHIELD); 
    wcex.hCursor = LoadCursor(NULL, IDC_ARROW); 
    wcex.hbrBackground = GetSysColorBrush(COLOR_WINDOW + 3); 
    wcex.lpszMenuName = NULL; 
    wcex.lpszClassName = szWindowClass; 
    wcex.hIconSm = NULL;
    return RegisterClassEx(&wcex); 
}

// FUNCTION: InitInstance (HANDLE, int)

BOOL InitInstance(HINSTANCE hInstance, int nCmdShow)
{
    HWND hWnd;
    hInst = hInstance; 
    hWnd = CreateWindow(szWindowClass, // window class name
        szTitle, // program name
        WS_OVERLAPPED | WS_SYSMENU, 
        400, // position on x
        0, // position on y
        718, 
        790, 
        NULL, 
        NULL,
        hInstance, 
        NULL); 
    if (!hWnd) 
    {
        return FALSE;
    }

    ShowWindow(hWnd, nCmdShow); 
    UpdateWindow(hWnd); 
    return TRUE;
}

// FUNCTION: WndProc (HWND, unsigned, WORD, LONG)

LRESULT CALLBACK WndProc(HWND hWnd, UINT message, WPARAM wParam, LPARAM lParam)
{
    PAINTSTRUCT ps;
    
    RECT rt;
    HPEN pen;
    
    static unsigned short index = 0, index1 = 0, strSize = 257;
    static char* str = new char[strSize];
    static unsigned short const strSize1 = 500;

    switch (message)
    {
    case WM_CREATE: //the message will appear when creating a window
        for (int i = 0; i < 7; i++)
        {
            for (int j = 0; j < 7; j++)
            {
                //serial numberoftheelement
                cells[i][j].x = j;
                cells[i][j].y = i;
                
                //setting the grid color
                cells[i][j].borderColor.r = 0 + 12 * (i + j);
                cells[i][j].borderColor.g = 0;
                cells[i][j].borderColor.b = 255 - 12 * (i + j);
                //setting the colorofthe circle
                cells[i][j].circleColor.r = rand() % 256;
                cells[i][j].circleColor.g = rand() % 256;
                cells[i][j].circleColor.b = rand() % 256;
                //setting textcolor
                cells[i][j].textColor.r = rand() % 256;
                cells[i][j].textColor.g = rand() % 256;
                cells[i][j].textColor.b = rand() % 256;
                //setting circleSize                
            }
        }
        break;

    case WM_PAINT: //redraw the widow
        hdc = BeginPaint(hWnd, &ps); //start graphical output
        GetClientRect(hWnd, &rt);
        SetBkMode(hdc, TRANSPARENT);
        
        //cycle of creating a grid with circles
        for (int i = 0; i < 7; i++)
        {
            for (int j = 0; j < 7; j++)
            {
                //Setting a custom pen and fill for the grid
                pen = CreatePen(PS_SOLID, 5, RGB(cells[i][j].borderColor.r, cells[i][j].borderColor.g, cells[i][j].borderColor.b));
                brush = CreateSolidBrush(RGB(cells[i][j].mainColor.r, cells[i][j].mainColor.g, cells[i][j].mainColor.b));
                SelectObject(hdc, brush);
                SelectObject(hdc, pen);

                //Meshing
                Rectangle(hdc, cells[i][j].x * rectSize, cells[i][j].y * rectSize + circleSize, (cells[i][j].x + 1) * rectSize, (cells[i][j].y + 1) * rectSize + circleSize);

                //Remove Penand Mesh Fill
                DeleteObject(pen);
                DeleteObject(brush);

                //Setting a custom pen and fill for circles
                
                if (i < 1 && j < 6) {
                    int z = 1 + rand() % (30 - 1);
                    //int z = 10;
                    pen = CreatePen(PS_SOLID, 5, RGB(cells[i][j].circleBorderColor.r, cells[i][j].circleBorderColor.g, cells[i][j].circleBorderColor.b));
                    brush = CreateSolidBrush(RGB(cells[i][j].circleColor.r, cells[i][j].circleColor.g, cells[i][j].circleColor.b));
                    SelectObject(hdc, brush);
                    SelectObject(hdc, pen);

                    //Making circles
                    Ellipse(hdc, cells[i][j].x * rectSize + z, cells[i][j].y * rectSize + z + circleSize, (cells[i][j].x + 1) * rectSize - z, (cells[i][j].y + 1) * rectSize - z + circleSize);

                    //Remove pen and circle fill
                    DeleteObject(pen);
                    DeleteObject(brush);
                    char arr[strSize1];
                    for (int i = 0; i < strSize1;)
                    {
                        char ch = rand() % 127;
                        if (isalnum(ch))
                        {
                            arr[i] = ch;
                            ++i;
                        }
                    }

                    // text output
                    SetTextColor(hdc, RGB(cells[i][j].textColor.r, cells[i][j].textColor.g, cells[i][j].textColor.b));
                    TextOut(hdc, cells[i][j].x * rectSize + 40, cells[i][j].y * rectSize + circleSize + 39, &arr[index++], 1);
                }
            }
        }
        //Displaying text on the screen
        
        EndPaint(hWnd, &ps);
        break;

    case WM_MOUSEMOVE:

        y = HIWORD(lParam);
        x = LOWORD(lParam);
        rt.top = 7;
        rt.left = 0;
        rt.right = 7 * rectSize;
        rt.bottom = circleSize;
    
        break;

    case WM_LBUTTONDOWN:

        yCoord = y;
        xCoord = x;

        yCoord -= circleSize;
        yCoord /= rectSize;
        xCoord /= rectSize;

        //Checking if coordinates are included in circle coordinates
        if (xCoord < 7 && yCoord < 7 && isInCircle(x, y - circleSize, xCoord * rectSize + rectSize / 2, yCoord * rectSize + rectSize / 2, (rectSize - 20) / 2)) {
            //InvalidateRect(hWnd, NULL, TRUE);
            
            GetPixel(hdc, x, y);
            flag = 1;
            flag = 1;
        }
        break;

    case WM_DESTROY:                //completion of work
        PostQuitMessage(0);
        break;

    default:
        //Processing messages that are not processed by the user
        return DefWindowProc(hWnd, message, wParam, lParam);
    }

    return 0;
}

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