Handling SDL events inside Win32 window - c

Question

I have difficulty handling SDL events inside a Win32 window. I made a small program to display magenta background. Basically when the user presses 'q' key, the background color should toggle from magenta to red and vice versa.
sdlwin.c
#include <windows.h>
#include <SDL2/SDL.h>
const int win_width = 500;
const int win_height = 450;
int b = 0;
LRESULT CALLBACK WndProc(HWND hWnd, UINT msg, WPARAM wParam, LPARAM lParam)
{
static SDL_Window *sdlWnd;
SDL_Surface *surface;
switch (msg)
{
case WM_CREATE:
if(SDL_Init(SDL_INIT_VIDEO) < 0)
{
MessageBox(hWnd, TEXT("SDL cannot be initialized!"), TEXT("Error!"),
MB_ICONEXCLAMATION | MB_OK);
PostQuitMessage(0);
}
sdlWnd = SDL_CreateWindowFrom(hWnd);
if (sdlWnd == NULL)
{
MessageBox(hWnd, TEXT("SDL window cannot be created!"), TEXT("Error!"),
MB_ICONEXCLAMATION | MB_OK);
SDL_Quit();
PostQuitMessage(0);
}
SDL_SetWindowTitle(sdlWnd, "SDL Window");
break;
case WM_PAINT:
surface = SDL_GetWindowSurface(sdlWnd);
SDL_FillRect(surface, &surface->clip_rect, b ? 0xFFFF00FF : 0xFFFF0000);
SDL_UpdateWindowSurface(sdlWnd);
break;
case WM_CLOSE:
SDL_DestroyWindow(sdlWnd);
SDL_Quit();
DestroyWindow(hWnd);
break;
case WM_DESTROY:
PostQuitMessage(0);
break;
default:
return DefWindowProc(hWnd, msg, wParam, lParam);
}
return 0;
}
int WINAPI WinMain(HINSTANCE hInstance, HINSTANCE hPrevInstance, LPSTR lpCmdLine, int nCmdShow)
{
const TCHAR szClassName[] = TEXT("MyClass");
WNDCLASS wc;
HWND hWnd;
MSG msg;
wc.style = CS_HREDRAW | CS_VREDRAW;
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)(COLOR_WINDOW+1);
wc.lpszMenuName = NULL;
wc.lpszClassName = szClassName;
wc.hIcon = LoadIcon(NULL, IDI_APPLICATION);
if (!RegisterClass(&wc))
{
MessageBox(NULL, TEXT("Window Registration Failed!"), TEXT("Error!"),
MB_ICONEXCLAMATION | MB_OK);
return 0;
}
hWnd = CreateWindow(szClassName,
TEXT("SDLWin"),
WS_OVERLAPPEDWINDOW | WS_VISIBLE,
CW_USEDEFAULT, CW_USEDEFAULT, win_width, win_height,
NULL, NULL, hInstance, NULL);
if (hWnd == NULL)
{
MessageBox(NULL, TEXT("Window Creation Failed!"), TEXT("Error!"),
MB_ICONEXCLAMATION | MB_OK);
return 0;
}
ShowWindow(hWnd, nCmdShow);
UpdateWindow(hWnd);
SDL_Event e;
while (GetMessage(&msg, NULL, 0, 0))
{
while (SDL_PollEvent(&e) != 0)
{
if (e.type == SDL_KEYDOWN && e.key.keysym.sym == SDLK_q)
{
b = !b;
//MessageBox(NULL, TEXT("bar"), TEXT("foo"), MB_ICONEXCLAMATION | MB_OK);
}
}
TranslateMessage(&msg);
DispatchMessage(&msg);
}
return (int) msg.wParam;
}
When I uncomment this line MessageBox(NULL, TEXT("bar"), TEXT("foo"), MB_ICONEXCLAMATION | MB_OK);, the window didn't respond when I press 'q' key but if I add this line, the window background color changed after I close the message box. I'm uncertain why this weird behaviour happens. My question is how to properly handle SDL events inside Win32 window. Any form of help is appreciated.

Answer 1

You need to call InvalidateRect(hWnd, NULL, TRUE/FALSE); after changing b.
That will post a WM_Paint message for your Window to redraw.