screen: implement terminal scrolling

src/screen.c

@@ -42,6 +42,23 @@ void terminal_putentryat(char c, uint8_t color, size_t x, size_t y)
         terminal_buffer[index] = vga_entry(c, color);
 }
 
+void terminal_scroll(void)
+{
+        for (size_t y = 0; y < VGA_HEIGHT - 1; y++) {
+                for (size_t x = 0; x < VGA_WIDTH; x++) {
+                        const size_t index_from = (y + 1) * VGA_WIDTH + x;
+                        const size_t index_to = y * VGA_WIDTH + x;
+                        terminal_buffer[index_to] = terminal_buffer[index_from];
+                }
+        }
+        for (size_t x = 0; x < VGA_WIDTH; x++) {
+                const size_t index = (VGA_HEIGHT - 1) * VGA_WIDTH + x;
+                terminal_buffer[index] = vga_entry(' ', terminal_color);
+        }
+        terminal_row = VGA_HEIGHT - 1;
+        terminal_column = 0;
+}
+
 void terminal_putchar(char c)
 {
 	if(c != '\n')
@@ -51,10 +68,10 @@ void terminal_putchar(char c)
                 terminal_column = 0;
 		terminal_initialize();
         	if (++terminal_row >= VGA_HEIGHT)
-                	terminal_row = 0;
+                	terminal_scroll();
 	}
 	if(terminal_row >= VGA_HEIGHT){
-		terminal_row = 0;
+		terminal_scroll();
 	}
 
 	if(c == '\n')