Question

How to use the SetPixel function to draw a diagonal line using the Win32 API in C

Answer 1

#include <windows.h>
#include <stdio.h>

LRESULT CALLBACK WndProc(HWND hWnd, UINT msg, WPARAM wParam, LPARAM lParam)
{
    switch (msg)
    {
        case WM_PAINT:
        {
            PAINTSTRUCT ps;
            HDC hdc = BeginPaint(hWnd, &ps);

            // Draw a red pixel
            SetPixel(hdc, 50, 50, RGB(255, 0, 0));

            // Read the pixel back
            COLORREF c = GetPixel(hdc, 50, 50);

            if (c != CLR_INVALID) {
                int r = GetRValue(c);
                int g = GetGValue(c);
                int b = GetBValue(c);

                wchar_t title[128];
                swprintf(title, 128, L"GetPixel Example - R=%d G=%d B=%d", r, g, b);

                SetWindowText(hWnd, title);
            }

            EndPaint(hWnd, &ps);
            return 0;
        }

        case WM_DESTROY:
            PostQuitMessage(0);
            return 0;
    }

    return DefWindowProc(hWnd, msg, wParam, lParam);
}

int WINAPI wWinMain(HINSTANCE hInstance, HINSTANCE hPrevInstance,
    PWSTR pCmdLine, int nCmdShow)
{
    const wchar_t CLASS_NAME[] = L"GetPixelDemo";

    WNDCLASS wc = { 0 };
    wc.lpfnWndProc = WndProc;
    wc.hInstance = hInstance;
    wc.lpszClassName = CLASS_NAME;

    RegisterClass(&wc);

    HWND hWnd = CreateWindowEx(
        0,
        CLASS_NAME,
        L"GetPixel Example",
        WS_OVERLAPPEDWINDOW,
        CW_USEDEFAULT, CW_USEDEFAULT,
        640, 480,
        NULL,
        NULL,
        hInstance,
        NULL
    );

    ShowWindow(hWnd, nCmdShow);

    MSG msg = { 0 };
    while (GetMessage(&msg, NULL, 0, 0))
    {
        TranslateMessage(&msg);
        DispatchMessage(&msg);
    }

    return 0;
}




/*
run:

GetPixel Example - R=255 G=0 B=0

*/

 

70+ SQL courses for beginners and professionals