Window won't update while changing its shape

Question

I have successfully created a window but it wont update the window to change its shape and color. I have tried to solve this for days an appreciate any help.

The program is meant to show an orange window that can be reshaped. It would also help, if you could check the code by compiling it in Visual Studios.

Here is the code:

#include <Windows.h>
#include "Header.h"

bool running = true;

void *buffer_memory;
int buffer_width;
int buffer_hight;
BITMAPINFO buffer_bitmap_info;

LRESULT CALLBACK windows_callback(HWND hwnd, UINT uMsg, WPARAM wParam, LPARAM lParam)
{
    LRESULT result = 0;
    switch (uMsg)
    {
        case WM_CLOSE:
        case WM_DESTROY:
            {
                running = false;
            }
            break;

        case WM_SIZE:
            {
                RECT rect;
                GetClientRect(hwnd, &rect);
                buffer_width = rect.left - rect.right;
                buffer_hight = rect.bottom - rect.top;
                int buffer_size = buffer_width *buffer_hight* sizeof(unsigned int);
                if (buffer_memory) VirtualFree(buffer_memory, 0, MEM_RELEASE);
                buffer_memory = VirtualAlloc(0, buffer_size, MEM_COMMIT | MEM_RESERVE, PAGE_READWRITE);
                buffer_bitmap_info.bmiHeader.biSize = sizeof(buffer_bitmap_info.bmiHeader);
                buffer_bitmap_info.bmiHeader.biWidth = buffer_width;
                buffer_bitmap_info.bmiHeader.biHeight = buffer_hight;
                buffer_bitmap_info.bmiHeader.biPlanes = 1;
                buffer_bitmap_info.bmiHeader.biBitCount = 32;
                buffer_bitmap_info.bmiHeader.biCompression = BI_RGB;
            }
            break;

        default:
            {
                result = DefWindowProc(hwnd, uMsg, wParam, lParam);
            }
    }
    return result;
}

int WinMain(HINSTANCE hInstance, HINSTANCE hPrevInstance, LPSTR lpCmdLine, int nShowCmd)
{
    //compile window
    CHAR clsName[] = "test";
    WNDCLASSA window_class = {};
    window_class.style = CS_HREDRAW | CS_VREDRAW;
    window_class.lpszClassName = clsName;
    window_class.lpfnWndProc = windows_callback;
    //register clases
    ATOM atom = RegisterClassA(&window_class);
    if (0 == atom)
    {
        DWORD err = GetLastError();
        return 1;
    }

    // create window
    HWND window = CreateWindow(clsName, "game", WS_OVERLAPPEDWINDOW | WS_VISIBLE, CW_USEDEFAULT,
        CW_USEDEFAULT, 720, 360, 0, 0, hInstance, 0);
    if (NULL == window)
    {

        DWORD err = GetLastError();
        return 1;
    }
    while (running)
    {
        HDC hdc = GetDC(window);
        // input

        // simulate
        MSG mesage;
        while (PeekMessage(&mesage, window, 0, 0, PM_REMOVE))
        {
            TranslateMessage(&mesage);
            DispatchMessage(&mesage);
        }
        unsigned int *pixel = (unsigned int *) buffer_memory;
        for (int y = 0; y < buffer_hight; y++)
        {
            for (int x = 0; x < buffer_width; x++)
            {

                *pixel++ = 0xff5500;
            }
        }
        // render
        StretchDIBits(hdc, 0, 0, buffer_width, buffer_hight, 0, 0, buffer_width, buffer_hight,
            buffer_memory, &buffer_bitmap_info, DIB_RGB_COLORS, SRCCOPY); {}
    }
};

Answer 1

The line: buffer_width = rect.left - rect.right;

=> buffer_width = rect.right- rect.left ;

You should draw in the WM_PAINT message,

case WM_PAINT:
    {
        PAINTSTRUCT ps;
        HDC hdc = BeginPaint(hwnd, &ps);
        unsigned int* pixel = (unsigned int*)buffer_memory;
        for (int y = 0; y < buffer_hight; y++)
        {
            for (int x = 0; x < buffer_width; x++)
            {

                *pixel++ = 0xff5500;
            }
        }
        // render
        StretchDIBits(hdc, 0, 0, buffer_width, buffer_hight, 0, 0, buffer_width, buffer_hight,
            buffer_memory, &buffer_bitmap_info, DIB_RGB_COLORS, SRCCOPY); {}
        EndPaint(hwnd, &ps);
    }
    break;

Updated:

#include <Windows.h>
//#include "Header.h"

bool running = true;

void* buffer_memory;
int buffer_width;
int buffer_hight;
BITMAPINFO buffer_bitmap_info;

LRESULT CALLBACK windows_callback(HWND hwnd, UINT uMsg, WPARAM wParam, LPARAM lParam)
{
    LRESULT result = 0;
    switch (uMsg)
    {
    case WM_CLOSE:
    case WM_DESTROY:
    {
        PostQuitMessage(0);
    }
    break;

    case WM_SIZE:
    {
        RECT rect;
        GetClientRect(hwnd, &rect);
        buffer_width = rect.right - rect.left;
        buffer_hight = rect.bottom - rect.top;
        int buffer_size = buffer_width * buffer_hight * sizeof(unsigned int);
        if (buffer_memory) VirtualFree(buffer_memory, 0, MEM_RELEASE);
        buffer_memory = VirtualAlloc(0, buffer_size, MEM_COMMIT | MEM_RESERVE, PAGE_READWRITE);
        buffer_bitmap_info.bmiHeader.biSize = sizeof(buffer_bitmap_info.bmiHeader);
        buffer_bitmap_info.bmiHeader.biWidth = buffer_width;
        buffer_bitmap_info.bmiHeader.biHeight = buffer_hight;
        buffer_bitmap_info.bmiHeader.biPlanes = 1;
        buffer_bitmap_info.bmiHeader.biBitCount = 32;
        buffer_bitmap_info.bmiHeader.biCompression = BI_RGB;
    }
    break;
    case WM_PAINT:
    {
        PAINTSTRUCT ps;
        HDC hdc = BeginPaint(hwnd, &ps);
        unsigned int* pixel = (unsigned int*)buffer_memory;
        for (int y = 0; y < buffer_hight; y++)
        {
            for (int x = 0; x < buffer_width; x++)
            {

                *pixel++ = 0xff5500;
            }
        }
        // render
        StretchDIBits(hdc, 0, 0, buffer_width, buffer_hight, 0, 0, buffer_width, buffer_hight,
            buffer_memory, &buffer_bitmap_info, DIB_RGB_COLORS, SRCCOPY); {}
        EndPaint(hwnd, &ps);
    }
    break;
    default:
    {
        result = DefWindowProc(hwnd, uMsg, wParam, lParam);
    }
    }
    return result;
}

int WinMain(HINSTANCE hInstance, HINSTANCE hPrevInstance, LPSTR lpCmdLine, int nShowCmd)
{
    //compile window
    CHAR clsName[] = "test";
    WNDCLASSA window_class = {};
    window_class.style = CS_HREDRAW | CS_VREDRAW;
    window_class.lpszClassName = clsName;
    window_class.lpfnWndProc = windows_callback;
    //register clases
    ATOM atom = RegisterClassA(&window_class);
    if (0 == atom)
    {
        DWORD err = GetLastError();
        return 1;
    }

    // create window
    HWND window = CreateWindow(clsName, "game", WS_OVERLAPPEDWINDOW | WS_VISIBLE, CW_USEDEFAULT,
        CW_USEDEFAULT, 720, 360, 0, 0, hInstance, 0);
    if (NULL == window)
    {

        DWORD err = GetLastError();
        return 1;
    }
    MSG msg;

    // Main message loop:
    while (GetMessage(&msg, nullptr, 0, 0))
    {     
         TranslateMessage(&msg);
         DispatchMessage(&msg);
    }
}