From 055c41adb342599cdffbb002b6f285f60f817320 Mon Sep 17 00:00:00 2001
From: =?UTF-8?q?Thomas=20Lov=C3=A9n?= <thomasloven@gmail.com>
Date: Mon, 4 Dec 2017 01:30:18 +0100
Subject: [PATCH] Scrolling screen when necessary

---
 src/kernel/drivers/vga.c  | 31 +++++++++++++++++++++------
 src/kernel/drivers/vga.tt | 44 +++++++++++++++++++++++++++++++++++++--
 2 files changed, 67 insertions(+), 8 deletions(-)

diff --git a/src/kernel/drivers/vga.c b/src/kernel/drivers/vga.c
index c1c3924..c28e7ef 100644
--- a/src/kernel/drivers/vga.c
+++ b/src/kernel/drivers/vga.c
@@ -2,17 +2,22 @@
 #include <memory.h>
 
 void *vidmem;
-struct {
-  uint8_t character;
-  uint8_t format;
-}__attribute__((packed)) buffer[VGA_SIZE];
+struct vga_cell{
+  uint8_t c;
+  uint8_t f;
+}__attribute__((packed));
+
+struct vga_cell buffer[VGA_SIZE];
 
 uint64_t cursor;
+uint8_t format;
 
 void vga_init()
 {
   vidmem = VGA_MEMORY;
   memset(vidmem, 0, VGA_SIZE*2);
+
+  format = 0x7;
 }
 
 void flush()
@@ -20,6 +25,20 @@ void flush()
   memcpy(vidmem, buffer, sizeof(buffer));
 }
 
+void scroll()
+{
+  while(cursor >= VGA_SIZE)
+  {
+    for(int i = 0; i < VGA_ROWS-1; i++)
+      for(int j = 0; j < VGA_COLS; j++)
+        buffer[VGA_POS(i, j)] = buffer[VGA_POS(i+1, j)];
+    for(int i = 0; i < VGA_COLS; i++)
+      buffer[VGA_POS(VGA_ROWS-1, i)] = (struct vga_cell){.c='\0', .f=format};
+  cursor -= VGA_COLS;
+  }
+
+}
+
 void vga_write(char c)
 {
   switch(c)
@@ -29,9 +48,9 @@ void vga_write(char c)
       cursor -= VGA_COL(cursor);
       break;
     default:
-      buffer[cursor].character = c;
-      buffer[cursor].format = 0x7;
+      buffer[cursor] = (struct vga_cell){.c = c, .f=format};
       cursor++;
   }
+  scroll();
   flush();
 }
diff --git a/src/kernel/drivers/vga.tt b/src/kernel/drivers/vga.tt
index 3e0971e..dab92f8 100644
--- a/src/kernel/drivers/vga.tt
+++ b/src/kernel/drivers/vga.tt
@@ -52,10 +52,10 @@ TEST(vga_write_adds_multiple_characters_to_vidmem)
 
 TEST(vga_writes_entire_screen_full)
 {
-  for(int i = 0; i < VGA_COLS*VGA_ROWS; i++)
+  for(int i = 0; i < (VGA_COLS*VGA_ROWS-1); i++)
     vga_write('x');
 
-  VGA_ASSERT_EQ(VGA_POS(VGA_ROWS-1, VGA_COLS-1), 'x');
+  VGA_ASSERT_EQ(VGA_POS(VGA_ROWS-1, VGA_COLS-2), 'x');
 }
 TEST(vga_does_not_overflow_memory_area)
 {
@@ -77,3 +77,43 @@ TEST(newline_moves_to_beginning_of_line)
   vga_write('b');
   VGA_ASSERT_EQ(VGA_POS(1,0), 'b');
 }
+
+void vga_write_str(char *str)
+{
+  while(*str) vga_write(*str++);
+}
+
+TEST(writing_past_end_of_screen_scrolls_screen_one_line)
+{
+  vga_write_str("1\n2\n3\n4\n5\n6\n7\n8\n9\n10\n");
+  vga_write_str("11\n12\n13\n14\n15\n16\n17\n18\n19\n20\n");
+  vga_write_str("21\n22\n23\n24\n");
+
+  vga_write_str("abcde");
+  VGA_ASSERT_EQ(0, '2');
+}
+TEST(screen_does_not_scroll_until_write)
+{
+  vga_write_str("1\n2\n3\n4\n5\n6\n7\n8\n9\n10\n");
+  vga_write_str("11\n12\n13\n14\n15\n16\n17\n18\n19\n20\n");
+  vga_write_str("21\n22\n23\n24");
+  vga_write_str("34567890123456789012345678901234567890123456789012345678901234567890123456789");
+
+  VGA_ASSERT_EQ(0, '1');
+}
+TEST(writing_past_end_of_screen_clears_last_line)
+{
+  vga_write_str("1\n2\n3\n4\n5\n6\n7\n8\n9\n10\n");
+  vga_write_str("11\n12\n13\n14\n15\n16\n17\n18\n19\n20\n");
+  vga_write_str("21\n22\n23\n24\n");
+  vga_write('a');
+  VGA_ASSERT_EQ(VGA_POS(VGA_ROWS-1, 1), '\0');
+}
+TEST(first_character_of_new_line_is_not_cleared)
+{
+  vga_write_str("1\n2\n3\n4\n5\n6\n7\n8\n9\n10\n");
+  vga_write_str("11\n12\n13\n14\n15\n16\n17\n18\n19\n20\n");
+  vga_write_str("21\n22\n23\n24\n");
+  vga_write('a');
+  VGA_ASSERT_EQ(VGA_POS(VGA_ROWS-1, 0), 'a');
+}