Don't force users to load rom from terminal or by dragging and dropping onto executable file. Instead, open a blank window and use SDL's drag&drop feature

include/emulator.hpp

@@ -47,7 +47,7 @@ class Emulator {
 	static constexpr u32 width = 400;
 	static constexpr u32 height = 240 * 2;  // * 2 because 2 screens
 	ROMType romType = ROMType::None;
-	bool running = true;
+	bool running = true, romLoaded = false;
 
 #ifdef PANDA3DS_ENABLE_HTTP_SERVER
 	HttpServer httpServer;

src/emulator.cpp

@@ -90,6 +90,7 @@ void Emulator::run() {
 	httpServer.startHttpServer();
 #endif
 	while (running) {
+		if(romLoaded) {
 #ifdef PANDA3DS_ENABLE_HTTP_SERVER
 			pollHttpServer();
 #endif
@@ -101,7 +102,7 @@ void Emulator::run() {
 			// Send VBlank interrupts
 			srv.sendGPUInterrupt(GPUInterrupt::VBlank0);
 			srv.sendGPUInterrupt(GPUInterrupt::VBlank1);
-
+		}
 		SDL_Event event;
 		while (SDL_PollEvent(&event)) {
 			namespace Keys = HID::Keys;
@@ -113,6 +114,7 @@ void Emulator::run() {
 					return;
 
 				case SDL_KEYDOWN:
+					if(romLoaded) {
 						switch (event.key.keysym.sym) {
 							case SDLK_l: srv.pressKey(Keys::A); break;
 							case SDLK_k: srv.pressKey(Keys::B); break;
@@ -150,9 +152,11 @@ void Emulator::run() {
 							case SDLK_RETURN: srv.pressKey(Keys::Start); break;
 							case SDLK_BACKSPACE: srv.pressKey(Keys::Select); break;
 						}
+					}
 					break;
 
 				case SDL_KEYUP:
+					if(romLoaded) {
 						switch (event.key.keysym.sym) {
 							case SDLK_l: srv.releaseKey(Keys::A); break;
 							case SDLK_k: srv.releaseKey(Keys::B); break;
@@ -183,9 +187,11 @@ void Emulator::run() {
 							case SDLK_RETURN: srv.releaseKey(Keys::Start); break;
 							case SDLK_BACKSPACE: srv.releaseKey(Keys::Select); break;
 						}
+					}
 					break;
 
-				case SDL_MOUSEBUTTONDOWN: {
+				case SDL_MOUSEBUTTONDOWN:
+					if(romLoaded) {
 						if (event.button.button == SDL_BUTTON_LEFT) {
 							const s32 x = event.button.x;
 							const s32 y = event.button.y;
@@ -203,15 +209,17 @@ void Emulator::run() {
 						} else if (event.button.button == SDL_BUTTON_RIGHT) {
 							holdingRightClick = true;
 						}
-					break;
 					}
+					break;
 
 				case SDL_MOUSEBUTTONUP:
+					if(romLoaded) {
 						if (event.button.button == SDL_BUTTON_LEFT) {
 							srv.releaseTouchScreen();
 						} else if (event.button.button == SDL_BUTTON_RIGHT) {
 							holdingRightClick = false;
 						}
+					}
 					break;
 
 				case SDL_CONTROLLERDEVICEADDED:
@@ -230,7 +238,8 @@ void Emulator::run() {
 					break;
 
 				case SDL_CONTROLLERBUTTONUP:
-				case SDL_CONTROLLERBUTTONDOWN: {
+				case SDL_CONTROLLERBUTTONDOWN:
+					if(romLoaded) {
 						u32 key = 0;
 
 						switch (event.cbutton.button) {
@@ -256,9 +265,11 @@ void Emulator::run() {
 							}
 						}
 					}
+					break;
 
 				// Detect mouse motion events for gyroscope emulation
-				case SDL_MOUSEMOTION: {
+				case SDL_MOUSEMOTION:
+					if(romLoaded) {
 						// We use right click to indicate we want to rotate the console. If right click is not held, then this is not a gyroscope rotation
 						if (!holdingRightClick) break;
 
@@ -272,11 +283,21 @@ void Emulator::run() {
 						const s32 pitch = motionY > 0 ? 0x7f : -0x7f;
 						srv.setRoll(roll);
 						srv.setPitch(pitch);
+					}
+					break;
+
+				case SDL_DROPFILE: {
+					char *droppedDir = event.drop.file;
+					if(droppedDir) {
+						loadROM(droppedDir);
+						free(droppedDir);
+					}
+				}
 				break;
 			}
 		}
-		}
 
+		if(romLoaded) {
 			if (gameController != nullptr) {
 				const s16 stickX = SDL_GameControllerGetAxis(gameController, SDL_CONTROLLER_AXIS_LEFTX);
 				const s16 stickY = SDL_GameControllerGetAxis(gameController, SDL_CONTROLLER_AXIS_LEFTY);
@@ -297,9 +318,10 @@ void Emulator::run() {
 					srv.setCirclepadY(-(stickY / div));
 				}
 			}
+			srv.updateInputs(cpu.getTicks());
+		}
 
 		// Update inputs in the HID module
-		srv.updateInputs(cpu.getTicks());
 		SDL_GL_SwapWindow(window);
 	}
 }
@@ -346,6 +368,7 @@ bool Emulator::loadROM(const std::filesystem::path& path) {
 		romType = ROMType::None;
 	}
 
+	romLoaded = success;
 	return success;
 }
 
@@ -390,6 +413,7 @@ bool Emulator::loadELF(std::ifstream& file) {
 	if (entrypoint.value() & 1) {
 		Helpers::panic("Misaligned ELF entrypoint. TODO: Check if ELFs can boot in thumb mode");
 	}
+
 	return true;
 }
 

src/main.cpp

@@ -5,11 +5,13 @@ int main (int argc, char *argv[]) {
 
     emu.initGraphicsContext();
 
-    auto romPath = std::filesystem::current_path() / (argc > 1 ? argv[1] : "teapot.elf");
+	if(argc > 1) {
+		auto romPath = std::filesystem::current_path() / argv[1];
 		if (!emu.loadROM(romPath)) {
 			// For some reason just .c_str() doesn't show the proper path
 			Helpers::panic("Failed to load ROM file: %s", romPath.string().c_str());
 		}
+	}
 
 	emu.run();
 }