Kernel: Optimize VTTY cursor rendering

cursor is now only updated once after all consecutive `putchar`s are
handled.

kernel/include/kernel/Terminal/TTY.h

@@ -41,7 +41,6 @@ namespace Kernel
 
 		virtual uint32_t height() const = 0;
 		virtual uint32_t width() const = 0;
-		void putchar(uint8_t ch);
 
 		virtual dev_t rdev() const final override { return m_rdev; }
 
@@ -60,10 +59,13 @@ namespace Kernel
 		TTY(mode_t mode, uid_t uid, gid_t gid);
 
 		virtual void putchar_impl(uint8_t ch) = 0;
+		virtual void update_cursor() {}
+
 		virtual BAN::ErrorOr<size_t> read_impl(off_t, BAN::ByteSpan) override;
 		virtual BAN::ErrorOr<size_t> write_impl(off_t, BAN::ConstByteSpan) override;
 
 	private:
+		void putchar(uint8_t ch);
 		void do_backspace();
 
 	protected:

kernel/include/kernel/Terminal/VirtualTTY.h

@@ -24,6 +24,7 @@ namespace Kernel
 	protected:
 		virtual BAN::StringView name() const override { return m_name; }
 		virtual void putchar_impl(uint8_t ch) override;
+		void update_cursor() override;
 
 	private:
 		VirtualTTY(BAN::RefPtr<TerminalDriver>);
@@ -78,6 +79,7 @@ namespace Kernel
 		uint32_t m_saved_row { 0 };
 		uint32_t m_saved_column { 0 };
 
+		bool m_cursor_shown { true };
 		uint32_t m_row { 0 };
 		uint32_t m_column { 0 };
 		Cell* m_buffer { nullptr };

kernel/kernel/Terminal/TTY.cpp

@@ -215,6 +215,7 @@ namespace Kernel
 			auto* ptr = reinterpret_cast<const uint8_t*>(ansi_c_str);
 			while (*ptr)
 				handle_input_byte(*ptr++);
+			update_cursor();
 		}
 	}
 
@@ -358,6 +359,7 @@ namespace Kernel
 		SpinLockGuard _(m_write_lock);
 		for (size_t i = 0; i < buffer.size(); i++)
 			putchar(buffer[i]);
+		update_cursor();
 		return buffer.size();
 	}
 
@@ -366,6 +368,7 @@ namespace Kernel
 		ASSERT(s_tty);
 		SpinLockGuard _(s_tty->m_write_lock);
 		s_tty->putchar(ch);
+		s_tty->update_cursor();
 	}
 
 	bool TTY::is_initialized()

kernel/kernel/Terminal/VirtualTTY.cpp

@@ -357,7 +357,7 @@ namespace Kernel
 			case 'l':
 				if (m_ansi_state.question && m_ansi_state.nums[0] == 25)
 				{
-					m_terminal_driver->set_cursor_shown(ch == 'h');
+					m_cursor_shown = (ch == 'h');
 					return reset_ansi();
 				}
 				reset_ansi();
@@ -518,8 +518,21 @@ namespace Kernel
 		}
 
 		putcodepoint(codepoint);
+	}
 
+	void VirtualTTY::update_cursor()
+	{
+		static bool last_shown = !m_cursor_shown;
+		if (m_cursor_shown != last_shown)
+			m_terminal_driver->set_cursor_shown(m_cursor_shown);
+		last_shown = m_cursor_shown;
+
+		static uint32_t last_column = -1;
+		static uint32_t last_row = -1;
+		if (last_column != m_column || last_row != m_row)
 			m_terminal_driver->set_cursor_position(m_column, m_row);
+		last_column = m_column;
+		last_row = m_row;
 	}
 
 }