该代码在硬件级别或更高级别上究竟做了什么？

Question

我正在阅读绘制圆的数学知识，它是有道理的，但将其翻译成 C++ 也是荒谬的。使用时似乎缺少一些基础数学或计算机功能 SetPixel(hdc, x, y , COLOREF bg); 在 Win32 API GDI 中。

但是，我设法找到了绘制圆的代码，但除了半径浮点值之外，我真的不明白它在任何级别上的作用 而*运算符与画圆有关。

谁能解释一下 这是做什么的，你是怎么想出来的？

//THIS CODE:
     float radius = 120.0;
                    for(int y =-radius; y<=radius; y++)
                    for(int x =-radius; x<=radius; x++)
                    if(x*x+y*y <= radius*radius)
                    SetPixel(DCWindowHandle, 200+x, 200+y, red);



//SCROLL DOWN HERE TO SEE IT IN USE:

#include <windows.h>
LRESULT CALLBACK WndProc(HWND , UINT , WPARAM , LPARAM);
int WINAPI WinMain(HINSTANCE hInstance, HINSTANCE hPrevInstance, PSTR szCmdLine, int iCmdShow)
{
    static TCHAR szAppName[] = TEXT ("Marble Engine");
    HWND WindowHandle;
    MSG Message;
    WNDCLASS WindowClass;
    WindowClass.style = CS_HREDRAW | CS_VREDRAW;
    WindowClass.lpfnWndProc = WndProc;
    WindowClass.cbClsExtra = 0;
    WindowClass.cbWndExtra = 0;
    WindowClass.hInstance = hInstance;
    WindowClass.hIcon = LoadIcon(NULL, IDI_APPLICATION);
    WindowClass.hCursor = LoadCursor(NULL, IDC_ARROW);
    WindowClass.hbrBackground = (HBRUSH) GetStockObject (WHITE_BRUSH);
    WindowClass.lpszMenuName = NULL;
    WindowClass.lpszClassName = szAppName;
    if(!RegisterClass (&WindowClass))
    {
        MessageBox(NULL, TEXT("This Program Requires Nothing!"),
        szAppName, MB_ICONERROR);
        return 0;
    }
    WindowHandle = CreateWindow(szAppName,
    TEXT ("The Shit Program!"),
    WS_OVERLAPPEDWINDOW,
    CW_USEDEFAULT,
    CW_USEDEFAULT,
    CW_USEDEFAULT,
    CW_USEDEFAULT,
    NULL,
    NULL,
    hInstance,
    NULL);
    ShowWindow(WindowHandle, iCmdShow);
    UpdateWindow(WindowHandle);
    while(GetMessage(&Message, NULL, 0, 0))
    {
        TranslateMessage(&Message);
        DispatchMessage(&Message);
    }
    return Message.wParam;
}
LRESULT CALLBACK WndProc(HWND WindowHandle, UINT Message, WPARAM wParam, LPARAM lParam)
{
    HDC DCWindowHandle;
    PAINTSTRUCT PaintStruct;
    RECT rect;
    TCHAR * text = TEXT("Hello there this is test!");
    COLORREF red = RGB(255, 0, 0);
    switch(Message)
    {
        case WM_CREATE:
        DCWindowHandle = GetDC(WindowHandle);
        ReleaseDC(WindowHandle, DCWindowHandle);
        return 0;
        case WM_PAINT:
        {
            DCWindowHandle = BeginPaint(WindowHandle, &PaintStruct);
            GetClientRect(WindowHandle, &rect);
            DrawText(DCWindowHandle, TEXT("Bother!"), -1, &rect, DT_SINGLELINE | DT_CENTER | DT_VCENTER);


            float radius = 120.0;

            for(int y =-radius; y<=radius; y++)
            for(int x =-radius; x<=radius; x++)
            if(x*x+y*y <= radius*radius)
            SetPixel(DCWindowHandle, 200+x, 200+y, red);

            EndPaint( WindowHandle, &PaintStruct);
            return 0;
        }
        case WM_DESTROY:
        PostQuitMessage(0);
        return 0;
    }
    return DefWindowProc(WindowHandle, Message, wParam , lParam);
}

Answer 1

这是画圆的效率较低的方法之一。它所做的是一个一个地遍历正方形中所有边长与圆的直径相同的像素。如果从像素到正方形中心的距离小于或等于圆的半径，则将该像素着色为红色。正方形中的所有其他像素保持不变。