Implement need_fullpath support

This makes it much less painful to specify disk images (as well as reduces memory consumption when loading!)

crates/retro_frontend/src/frontend.rs

@@ -68,6 +68,7 @@ pub struct Frontend {
 	pub(crate) game_loaded: bool,
 
 	pub(crate) av_info: Option<SystemAvInfo>,
+	pub(crate) sys_info: Option<SystemInfo>,
 
 	/// The core's requested pixel format.
 	/// TODO: HW accel. (or just not care)
@@ -114,6 +115,7 @@ impl Frontend {
 			game_loaded: false,
 
 			av_info: None,
+			sys_info: None,
 
 			pixel_format: PixelFormat::RGB565,
 			converted_pixel_buffer: Vec::new(),
@@ -374,32 +376,46 @@ impl Frontend {
 			return Err(Error::CoreNotLoaded);
 		}
 
-		// For now I'm only implementing the gameinfo garbage that
-		// makes you read the whole file in. Later on I'll look into VFS
-		// support; but for now, it seems more cores will probably
-		// play ball with this.. which sucks :(
-
 		// I'm aware this is nasty but bleh
 		let slice = path.as_ref().as_os_str().as_bytes();
 		let path_string = CString::new(slice).expect("shouldn't fail");
-		let contents = fs::read(path)?;
 
-		let gameinfo = GameInfo {
+		let system_info = self.get_system_info()?;
-			path: path_string.as_ptr(),
-			data: contents.as_ptr() as *const ffi::c_void,
-			size: contents.len(),
-			meta: std::ptr::null(),
-		};
 
 		let core_api = self.core_api.as_ref().unwrap();
 
-		unsafe {
+		let mut gameinfo = GameInfo {
-			if !(core_api.retro_load_game)(&gameinfo) {
+			path: path_string.as_ptr(),
-				return Err(Error::RomLoadFailed);
+			data: std::ptr::null(),
-			}
+			size: 0,
+			meta: std::ptr::null(),
+		};
 
-			self.game_loaded = true;
+		// If the core does not need fullpath, then
-			Ok(())
+		// read the file data into a buffer we give to the core.
+		// This is pretty wasteful but works.
+		if !system_info.need_fullpath {
+			let contents = fs::read(path)?;
+			gameinfo.data = contents.as_ptr() as *const ffi::c_void;
+			gameinfo.size = contents.len();
+
+			unsafe {
+				if !(core_api.retro_load_game)(&gameinfo) {
+					return Err(Error::RomLoadFailed);
+				}
+
+				self.game_loaded = true;
+				Ok(())
+			}
+		} else {
+			unsafe {
+				if !(core_api.retro_load_game)(&gameinfo) {
+					return Err(Error::RomLoadFailed);
+				}
+
+				self.game_loaded = true;
+				Ok(())
+			}
 		}
 	}
 
@@ -443,6 +459,28 @@ impl Frontend {
 		}
 	}
 
+	pub fn get_system_info(&mut self) -> Result<SystemInfo> {
+		if !self.core_loaded() {
+			return Err(Error::CoreNotLoaded);
+		}
+
+		if let Some(sys) = self.sys_info.as_ref() {
+			Ok(sys.clone())
+		} else {
+			let mut sys_info: MaybeUninit<SystemInfo> = MaybeUninit::uninit();
+
+			// Actually get the system info
+			unsafe {
+				let core_api = self.core_api.as_ref().unwrap();
+				(core_api.retro_get_system_info)(sys_info.as_mut_ptr());
+
+				self.sys_info = Some(sys_info.assume_init());
+			}
+
+			Ok(self.sys_info.as_ref().unwrap().clone())
+		}
+	}
+
 	pub fn get_size(&mut self) -> (u32, u32) {
 		(self.fb_width, self.fb_height)
 	}