From 760884de78377935896272237b1300d721da3654 Mon Sep 17 00:00:00 2001
From: Eryn Wells <eryn@erynwells.me>
Date: Sat, 27 Feb 2016 15:07:52 -0500
Subject: [PATCH] Console can scroll now!

---
 src/Console.cc | 49 +++++++++++++++++++++++++++++++++++++++++--------
 src/Console.hh |  4 +++-
 src/Main.cc    | 19 +++++++++++++++++--
 3 files changed, 61 insertions(+), 11 deletions(-)

diff --git a/src/Console.cc b/src/Console.cc
index 9966386..c24292f 100644
--- a/src/Console.cc
+++ b/src/Console.cc
@@ -38,9 +38,8 @@ Console::Console()
 
 
 void
-Console::clear(Console::Color color)
+Console::clear()
 {
-    setColor(Color::LightGray, color);
     for (size_t y = 0; y < Console::Height; y++) {
         for (size_t x = 0; x < Console::Width; x++) {
             putEntryAt(x, y, ' ', mColor);
@@ -49,21 +48,31 @@ Console::clear(Console::Color color)
 }
 
 
+void
+Console::clear(Console::Color color)
+{
+    setColor(Color::LightGray, color);
+    clear();
+}
+
+
 void
 Console::writeChar(char c)
 {
     switch (c) {
         case '\n':
             mCursor.col = 0;
-            if (++mCursor.row == Console::Height) {
-                mCursor.row = 0;
+            if (++mCursor.row >= Console::Height) {
+                scroll();
+                mCursor.row = Console::Height - 1;
             }
             break;
         case '\t':
             mCursor.col += 8;
             if (mCursor.col >= Console::Width) {
-                if (++mCursor.row == Console::Height) {
-                    mCursor.row = 0;
+                if (++mCursor.row >= Console::Height) {
+                    scroll();
+                    mCursor.row = Console::Height - 1;
                 }
                 mCursor.col %= Console::Width;
             }
@@ -72,8 +81,9 @@ Console::writeChar(char c)
             putEntryAt(mCursor.col, mCursor.row, c, mColor);
             if (++mCursor.col == Console::Width) {
                 mCursor.col = 0;
-                if (++mCursor.row == Console::Height) {
-                    mCursor.row = 0;
+                if (++mCursor.row >= Console::Height) {
+                    scroll();
+                    mCursor.row = Console::Height - 1;
                 }
             }
             break;
@@ -111,4 +121,27 @@ Console::putEntryAt(size_t x,
     mBase[index] = makeVGAEntry(c, color);
 }
 
+void
+Console::scroll(size_t lines)
+{
+    if (lines == 0) {
+        return;
+    }
+
+    if (lines > Console::Height) {
+        clear();
+        return;
+    }
+
+    uint16_t *dst = mBase;
+    uint16_t *src = mBase + lines * Console::Width;
+    uint16_t *const end = mBase + Console::Width * Console::Height;
+    while (src < end) {
+        *dst++ = *src++;
+    }
+    while (dst < end) {
+        *dst++ = makeVGAEntry(' ', mColor);
+    }
+}
+
 } /* namespace kernel */
diff --git a/src/Console.hh b/src/Console.hh
index b205d5f..dcc0537 100644
--- a/src/Console.hh
+++ b/src/Console.hh
@@ -44,7 +44,8 @@ struct Console
     Console();
 
     /** Clear the console to the provided color. */
-    void clear(Color color = Color::Black);
+    void clear();
+    void clear(Color color);
 
     /** Write a character to the terminal at the current cursor position. */
     void writeChar(char c);
@@ -60,6 +61,7 @@ private:
     uint8_t mColor;
 
     void putEntryAt(size_t x, size_t y, char c, uint8_t color);
+    void scroll(size_t lines = 1);
 };
 
 } /* namespace kernel */
diff --git a/src/Main.cc b/src/Main.cc
index 77d0270..ebdab01 100644
--- a/src/Main.cc
+++ b/src/Main.cc
@@ -18,8 +18,23 @@ kearly()
     kernel::Console console;
     console.clear(kernel::Console::Color::Blue);
     console.writeString("Hello world!\n");
-    console.writeString("a\nb\nc\n");
-    console.writeString("abc\tdef\tghi\tjkl\tmno\n");
+
+    volatile int foo = 0;
+    int j = 0;
+    int i = 0;
+    for (;;) {
+        if (j == 0) {
+            console.writeString("--- MARK ---\n");
+        }
+        console.writeChar('a' + i);
+        console.writeChar('\n');
+        i = (i + 1) % 26;
+        j = (j + 1) % 500;
+
+        for (uint32_t k = 0; k < (2u << 27) - 1; k++) {
+            foo /= 2;
+        }
+    }
 }