计算机图形学 中点画线法绘制三条任意斜率的平行直线（相关搜索：计算机图形学）（相关搜索：计算机图形学）

Question

费脑！大学生计算机图形学实验报告！
题目：OpenGL下中点画线法绘制三条任意斜率的平行直线
问题：我一直出不来 但是没有报错
以下是代码

```c++
#include <windows.h>
#include <gl/gl.h>
#include <cstdio>

// 函数声明
LRESULT CALLBACK WndProc(HWND hWnd, UINT message, WPARAM wParam, LPARAM lParam);
void EnableOpenGL(HWND hWnd, HDC *hDC, HGLRC *hRC);
void DisableOpenGL(HWND hWnd, HDC hDC, HGLRC hRC);
void midpointLine(int x0, int y0, int x1, int y1);

// 全局变量
BOOL bQuit = FALSE;
float theta = 0.0f;

int WINAPI WinMain(HINSTANCE hInstance, HINSTANCE hPrevInstance, LPSTR lpCmdLine, int iCmdShow)
{
    WNDCLASS wc;
    HWND hWnd;
    HDC hDC;
    HGLRC hRC;
    MSG msg;

    // 注册窗口类
    wc.style = CS_OWNDC;
    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(BLACK_BRUSH);
    wc.lpszMenuName = NULL;
    wc.lpszClassName = "GLSample";
    RegisterClass(&wc);

    // 创建主窗口
    hWnd = CreateWindow(
        "GLSample", "OpenGL Sample",
        WS_CAPTION | WS_POPUPWINDOW | WS_VISIBLE,
        0, 0, 256, 256,
        NULL, NULL, hInstance, NULL);

    // 启用 OpenGL
    EnableOpenGL(hWnd, &hDC, &hRC);

    // 程序主循环
    while (!bQuit)
    {
        // 检查消息
        if (PeekMessage(&msg, NULL, 0, 0, PM_REMOVE))
        {
            // 处理消息
            if (msg.message == WM_QUIT)
            {
                bQuit = TRUE;
            }
            else
            {
                TranslateMessage(&msg);
                DispatchMessage(&msg);
            }
        }
        else
        {
            std::printf("Inside main loop.\n");
            // OpenGL 绘制
            glClearColor(0.0f, 0.0f, 0.0f, 0.0f);
            glClear(GL_COLOR_BUFFER_BIT);

            // 设置直线颜色为白色
            glColor3f(1.0f, 1.0f, 1.0f);
            std::printf("Set line color to white.\n");
            // 绘制三条平行直线
           
            midpointLine(50, 50, 150, 150);
            midpointLine(50, 55, 150, 155);
            midpoin