Question

How to draw a rectangle on a window in C Win32 API

Answer 1

#define WIN32_LEAN_AND_MEAN
#define NOMINMAX

#include <windows.h>
#include <stdint.h>
#include <stdbool.h>

typedef uint32_t u32;

unsigned int client_width = 600;
unsigned int client_height = 600;

void* memory;
BITMAPINFO bitmap_info;

void ClearScreen(u32 color);
void DrawRectangle(int rec_x, int rec_y, int rec_width, int rec_height, u32 color);

LRESULT CALLBACK WndProc(HWND hwnd, UINT msg, WPARAM wparam, LPARAM lparam);

int CALLBACK WinMain(HINSTANCE hInstance, HINSTANCE hPrevInstance, LPSTR lpCmdLine, int nCmdShow) {
    WNDCLASS window_class = { 0 };

    wchar_t class_name[] = L"WindowClassName";

    window_class.lpfnWndProc = WndProc;
    window_class.hInstance = hInstance;
    window_class.lpszClassName = class_name;
    window_class.hCursor = LoadCursor(0, IDC_CROSS);

    RECT window_rect;
    window_rect.left = 0;
    window_rect.top = 0;
    window_rect.right = client_width;
    window_rect.bottom = client_height;

    AdjustWindowRectEx(&window_rect,
        WS_OVERLAPPEDWINDOW,
        0, 0
    );

    int window_width = window_rect.right - window_rect.left;
    int window_height = window_rect.bottom - window_rect.top;

    int screen_width = GetSystemMetrics(SM_CXSCREEN);
    int screen_height = GetSystemMetrics(SM_CYSCREEN);

    int window_x = (screen_width / 2) - (window_width / 2);
    int window_y = (screen_height / 2) - (window_height / 2);

    RegisterClass(&window_class);

    HWND window = CreateWindowEx(0,
        class_name,
        L"Draw Rectangle",
        WS_OVERLAPPEDWINDOW | WS_VISIBLE,
        window_x,
        window_y,
        window_width,
        window_height,
        0,
        0,
        hInstance,
        0);

    memory = VirtualAlloc(0,
        client_width * client_height * 4,
        MEM_RESERVE | MEM_COMMIT,
        PAGE_READWRITE
    );

    bitmap_info.bmiHeader.biSize = sizeof(bitmap_info.bmiHeader);
    bitmap_info.bmiHeader.biWidth = client_width;
    bitmap_info.bmiHeader.biHeight = client_height;
    bitmap_info.bmiHeader.biPlanes = 1;
    bitmap_info.bmiHeader.biBitCount = 32;
    bitmap_info.bmiHeader.biCompression = BI_RGB;

    HDC hdc = GetDC(window);

    bool running = true;
    while (running)
    {
        MSG msg;
        while (PeekMessageW(&msg, 0, 0, 0, PM_REMOVE))
        {
            if (msg.message == WM_QUIT) {
                running = false;
            }
            TranslateMessage(&msg);
            DispatchMessageW(&msg);
        }

        ClearScreen(0x999999);

        DrawRectangle(200, 300, 100, 100, 0x3389E2); // from bottom left

        // The StretchDIBits function copies the color data for a rectangle of pixels 
        // in a DIB, JPEG, or PNG image to the specified destination rectangle.

        StretchDIBits(hdc,
            0,
            0,
            client_width,
            client_height,
            0,
            0,
            client_width,
            client_height,
            memory,
            &bitmap_info,
            DIB_RGB_COLORS,
            SRCCOPY
        );
    }

    return 0;
}

LRESULT CALLBACK WndProc(HWND hwnd, UINT msg, WPARAM wparam, LPARAM lparam) {
    LRESULT result = 0;

    switch (msg)
    {
        case WM_KEYDOWN:
        {
            if (wparam == VK_ESCAPE) {
                DestroyWindow(hwnd);
            }
            break;
        }
        case WM_DESTROY:
        {
            PostQuitMessage(0);
            break;
        }
        default:
            result = DefWindowProcW(hwnd, msg, wparam, lparam);
        }

    return result;
}

void ClearScreen(u32 color) {
    u32* pixel = (u32*)memory;

    for (u32 i = 0; i < client_width * client_height; i++) {
        *pixel++ = color;
    }
}

void DrawRectangle(int rec_x, int rec_y, int rec_width, int rec_height, u32 color) {
    u32* pixel = (u32*)memory;
    pixel += rec_y * client_width + rec_x;

    for (int y = 0; y < rec_height; y++) {
        for (int x = 0; x < rec_width; x++) {
            *pixel++ = color;
        }

        pixel += client_width - rec_width;
    }
}



/*
run:



*/

 

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