Kernel: Implement fast scrolling for TTY

kernel/include/kernel/Device/FramebufferDevice.h

@@ -17,6 +17,10 @@ namespace Kernel
 
 		void set_pixel(uint32_t x, uint32_t y, uint32_t rgb);
 
+		// positive rows -> empty pixels on bottom
+		// negative rows -> empty pixels on top
+		void scroll(int32_t rows, uint32_t rgb);
+
 		void sync_pixels_full();
 		void sync_pixels_linear(uint32_t first_pixel, uint32_t pixel_count);
 		void sync_pixels_rectangle(uint32_t top_right_x, uint32_t top_right_y, uint32_t width, uint32_t height);

kernel/include/kernel/Terminal/FramebufferTerminal.h

@@ -15,6 +15,7 @@ namespace Kernel
 		virtual uint32_t height() const override { return m_framebuffer_device->height() / font().height(); }
 
 		virtual void putchar_at(uint16_t, uint32_t, uint32_t, Color, Color) override;
+		virtual bool scroll(Color) override;
 		virtual void clear(Color) override;
 
 		virtual void set_cursor_position(uint32_t, uint32_t) override;

kernel/include/kernel/Terminal/TerminalDriver.h

@@ -31,6 +31,7 @@ namespace Kernel
 		virtual uint32_t height() const = 0;
 
 		virtual void putchar_at(uint16_t, uint32_t, uint32_t, Color, Color) = 0;
+		virtual bool scroll(Color) { return false; }
 		virtual void clear(Color) = 0;
 
 		virtual void set_cursor_position(uint32_t, uint32_t) = 0;

kernel/kernel/Device/FramebufferDevice.cpp

@@ -135,6 +135,25 @@ namespace Kernel
 			video_buffer_u8[(y * m_width + x) * (BANAN_FB_BPP / 8) + 3] = rgb >> 24;
 	}
 
+	void FramebufferDevice::scroll(int32_t rows, uint32_t rgb)
+	{
+		if (rows == 0)
+			return;
+		rows = BAN::Math::clamp<int32_t>(rows, -m_height, m_height);
+		const uint32_t abs_rows = BAN::Math::abs(rows);
+
+		auto* video_buffer_u8 = reinterpret_cast<uint8_t*>(m_video_buffer->vaddr());
+		uint8_t* src = (rows < 0) ? video_buffer_u8 : &video_buffer_u8[(abs_rows * m_width) * (BANAN_FB_BPP / 8)];
+		uint8_t* dst = (rows > 0) ? video_buffer_u8 : &video_buffer_u8[(abs_rows * m_width) * (BANAN_FB_BPP / 8)];
+		memmove(dst, src, (m_height - abs_rows) * m_width * (BANAN_FB_BPP / 8));
+
+		uint32_t start_y = (rows < 0) ? 0 : m_height - abs_rows;
+		uint32_t stop_y  = (rows < 0) ? abs_rows : m_height;
+		for (uint32_t y = start_y; y < stop_y; y++)
+			for (uint32_t x = 0; x < m_width; x++)
+				set_pixel(x, y, rgb);
+	}
+
 	void FramebufferDevice::sync_pixels_full()
 	{
 		auto* video_memory_u8 = reinterpret_cast<uint8_t*>(m_video_memory_vaddr);

kernel/kernel/Terminal/FramebufferTerminal.cpp

@@ -33,6 +33,13 @@ namespace Kernel
 		m_framebuffer_device->sync_pixels_rectangle(x, y, font().width(), font().height());
 	}
 
+	bool FramebufferTerminalDriver::scroll(Color color)
+	{
+		m_framebuffer_device->scroll(font().height(), color.rgb);
+		m_framebuffer_device->sync_pixels_full();
+		return true;
+	}
+
 	void FramebufferTerminalDriver::clear(Color color)
 	{
 		for (uint32_t y = 0; y < m_framebuffer_device->height(); y++)

kernel/kernel/Terminal/VirtualTTY.cpp

@@ -99,8 +99,8 @@ namespace Kernel
 			render_from_buffer(last_x, last_y);
 		if (m_show_cursor)
 			m_terminal_driver->set_cursor_position(x, y);
-		last_x = m_column = x;
-		last_y = m_row = y;
+		last_x = x;
+		last_y = y;
 	}
 
 	void VirtualTTY::reset_ansi()
@@ -410,10 +410,18 @@ namespace Kernel
 			for (uint32_t x = 0; x < m_width; x++)
 				m_buffer[(m_height - 1) * m_width + x] = { .foreground = m_foreground, .background = m_background, .codepoint = ' ' };
 
-			// Render the whole buffer to the screen
-			for (uint32_t y = 0; y < m_height; y++)
-				for (uint32_t x = 0; x < m_width; x++)
-					render_from_buffer(x, y);
+			// hide cursor during scrolling
+			bool old_show_cursor = m_show_cursor;
+			m_show_cursor = false;
+			set_cursor_position(0, 0);
+			if (!m_terminal_driver->scroll(m_background))
+			{
+				// No fast scrolling, render the whole buffer to the screen
+				for (uint32_t y = 0; y < m_height; y++)
+					for (uint32_t x = 0; x < m_width; x++)
+						render_from_buffer(x, y);
+			}
+			m_show_cursor = old_show_cursor;
 
 			m_column = 0;
 			m_row--;