Creating an Overlay Window in SDL
How can I create an overlay window that always stays on top of other windows?
Creating an overlay window in SDL that always stays on top of other SDL windows involves a combination of SDL window flags and platform-specific techniques.
SDL itself doesn't directly support "always on top" windows, but you can achieve this effect with a few tricks.
Creating the Overlay Window
First, create the window with the appropriate SDL flags. Typically, you would want the window to be borderless to give it an overlay-like appearance:
#include <SDL.h>
class OverlayWindow {
public:
OverlayWindow() {
SDLWindow = SDL_CreateWindow(
"Overlay Window",
SDL_WINDOWPOS_CENTERED, SDL_WINDOWPOS_CENTERED,
400, 300,
SDL_WINDOW_BORDERLESS | SDL_WINDOW_ALWAYS_ON_TOP
);
}
~OverlayWindow() {
SDL_DestroyWindow(SDLWindow);
}
SDL_Window* SDLWindow{nullptr};
};
int main(int argc, char** argv) {
SDL_Init(SDL_INIT_VIDEO);
OverlayWindow overlay;
SDL_Event Event;
while (true) {
while (SDL_PollEvent(&Event)) {
if (Event.type == SDL_QUIT) {
return 0;
}
}
}
SDL_Quit();
return 0;
}Platform-Specific Adjustments
To make the window stay on top, you might need to use platform-specific APIs. Here's how you can achieve this on Windows using the Win32 API:
#include <SDL.h>
#include <SDL_syswm.h>
#include <windows.h>
class OverlayWindow {
public:
OverlayWindow() {
SDLWindow = SDL_CreateWindow(
"Overlay Window",
SDL_WINDOWPOS_CENTERED,
SDL_WINDOWPOS_CENTERED,
400, 300,
SDL_WINDOW_BORDERLESS
);
HWND hwnd = GetSDLWindowHandle(SDLWindow);
SetWindowPos(hwnd, HWND_TOPMOST, 0, 0, 0, 0,
SWP_NOMOVE | SWP_NOSIZE);
}
~OverlayWindow() {
SDL_DestroyWindow(SDLWindow);
}
SDL_Window* SDLWindow{nullptr};
private:
HWND GetSDLWindowHandle(SDL_Window* window) {
SDL_SysWMinfo wmInfo;
SDL_VERSION(&wmInfo.version);
SDL_GetWindowWMInfo(window, &wmInfo);
return wmInfo.info.win.window;
}
};
int main(int argc, char** argv) {
SDL_Init(SDL_INIT_VIDEO);
OverlayWindow overlay;
SDL_Event Event;
while (true) {
while (SDL_PollEvent(&Event)) {
if (Event.type == SDL_QUIT) {
return 0;
}
}
}
SDL_Quit();
return 0;
}In this example, SetWindowPos() is used to set the window as always on top (HWND_TOPMOST).
Considerations
- Cross-Platform: For a cross-platform solution, you would need to implement similar logic using respective platform-specific APIs for macOS and Linux.
- User Experience: Always-on-top windows can be intrusive. Ensure this behavior is appropriate for your application's use case.
- Focus Management: Handle focus and input appropriately. Overlay windows should not disrupt the main application's usability.
Creating an overlay window in SDL involves combining SDL's window creation functions with platform-specific code to achieve the desired always-on-top behavior.
Managing Window Input Focus
Learn how to manage and control window input focus in SDL applications, including how to create, detect, and manipulate window focus states.