在c++中使用GDI绘制抛物线，并通过事件监听实现抛物线的放大、缩小、移动

在C++中使用GDI（Graphics Device Interface）绘制抛物线可以通过以下步骤实现：

1. 首先需要包含Windows.h头文件和链接Gdi32.lib库文件。

2. 创建窗口和设备上下文。

3. 在设备上下文中使用GDI绘制抛物线，可以使用MoveToEx和LineTo函数绘制直线，使用Arc函数绘制圆弧。

4. 创建事件处理函数来处理放大、缩小、移动事件，可以使用SetWindowPos函数来重新定位和调整窗口大小。

下面是一个简单的示例代码：

#include <Windows.h>
#include <iostream>

using namespace std;

LRESULT CALLBACK WndProc(HWND, UINT, WPARAM, LPARAM);

int WINAPI WinMain(HINSTANCE hInstance, HINSTANCE hPrevInstance, LPSTR lpCmdLine, int nCmdShow)
{
    WNDCLASS wc;
    HWND hwnd;
    MSG msg;

    // Registering the Window Class
    wc.style = CS_HREDRAW | CS_VREDRAW;
    wc.lpfnWndProc = WndProc;
    wc.cbClsExtra = 0;
    wc.cbWndExtra = 0;
    wc.hInstance = hInstance;
    wc.hIcon = LoadIcon(NULL, IDI_APPLICATION);
    wc.hCursor = LoadCursor(NULL, IDC_ARROW);
    wc.hbrBackground = (HBRUSH)GetStockObject(WHITE_BRUSH);
    wc.lpszMenuName = NULL;
    wc.lpszClassName = "WindowClass";
    RegisterClass(&wc);

    // Creating the Window
    hwnd = CreateWindow("WindowClass", "Parabola",
        WS_OVERLAPPEDWINDOW, CW_USEDEFAULT, CW_USEDEFAULT,
        800, 600, NULL, NULL, hInstance, NULL);

    ShowWindow(hwnd, nCmdShow);
    UpdateWindow(hwnd);

    // Message Loop
    while (GetMessage(&msg, NULL, 0, 0))
    {
        TranslateMessage(&msg);
        DispatchMessage(&msg);
    }

    return msg.wParam;
}

LRESULT CALLBACK WndProc(HWND hwnd, UINT msg, WPARAM wParam, LPARAM lParam)
{
    static int scale = 1;
    static int x = 0;
    static int y = 0;
    static int xSpeed = 5;

    switch (msg)
    {
    case WM_PAINT:
    {
        // Drawing the Parabola
        PAINTSTRUCT ps;
        HDC hdc = BeginPaint(hwnd, &ps);

        HPEN hPen = CreatePen(PS_SOLID, 2, RGB(255, 0, 0));
        SelectObject(hdc, hPen);

        int a = 10 * scale;
        int b = 20 * scale;

        for (int i = -400; i <= 400; i++)
        {
            int x1 = i;
            int y1 = ((x1 - x) * (x1 - x)) / (4 * a) + y;

            if (y1 < 600)
            {
                SetPixel(hdc, x1 + 400, 600 - y1, RGB(255, 0, 0));
            }
        }

        EndPaint(hwnd, &ps);
        break;
    }
    case WM_KEYDOWN:
    {
        // Handling the Key Events
        switch (wParam)
        {
        case VK_UP:
            scale++;
            InvalidateRect(hwnd, NULL, TRUE);
            break;
        case VK_DOWN:
            scale--;
            if (scale < 1) scale = 1;
            InvalidateRect(hwnd, NULL, TRUE);
            break;
        case VK_LEFT:
            x -= 10;
            InvalidateRect(hwnd, NULL, TRUE);
            break;
        case VK_RIGHT:
            x += 10;
            InvalidateRect(hwnd, NULL, TRUE);
            break;
        }
        break;
    }
    case WM_TIMER:
    {
        // Handling the Timer Events
        x += xSpeed;
        if (x > 400) xSpeed = -5;
        if (x < -400) xSpeed = 5;
        InvalidateRect(hwnd, NULL, TRUE);
        break;
    }
    case WM_DESTROY:
        PostQuitMessage(0);
        break;
    default:
        return DefWindowProc(hwnd, msg, wParam, lParam);
    }

    return 0;
}

这个示例程序可以通过上下左右键和定时器事件来控制抛物线的放大、缩小、移动和动画效果。你可以根据自己的需要修改代码来实现更多功能。