From 65a4b94be100d795528202464b7d6f4b72e53734 Mon Sep 17 00:00:00 2001
From: Nathan Cannon <neviynhd@gmail.com>
Date: Sun, 22 Oct 2017 01:54:51 +0100
Subject: [PATCH] Scrolling now works. Simplified access to VGA memory.

---
 kernel/arch/i386/tty.nim | 36 ++++++++++++++++++++----------------
 kernel/arch/i386/vga.nim |  6 ++++--
 kernel/kernel.nim        |  3 +++
 3 files changed, 27 insertions(+), 18 deletions(-)

diff --git a/kernel/arch/i386/tty.nim b/kernel/arch/i386/tty.nim
index 90aee3f..baf7c3f 100644
--- a/kernel/arch/i386/tty.nim
+++ b/kernel/arch/i386/tty.nim
@@ -1,18 +1,21 @@
 import vga
 
+type
+  VGAMemory = ptr array[0..2000, VGADoubleByte]
+
 const
   vgaWidth = 80
   vgaHeight = 25
   terminalBufferBaseAddress = 0xB8000
-  bufferWidthSkip = vgaWidth * 2
+  vgaMem = cast[VGAMemory](terminalBufferBaseAddress)
 
 var
   terminalRow, terminalColumn = 0
   terminalColour: int
 
 proc terminalWriteAtPoint(writeChar: char, colour: int, xPos: int, yPos: int) =
-  let index = terminalBufferBaseAddress + (yPos * bufferWidthSkip + (xPos * 2))
-  cast[ptr int16](index)[] = vga.vgaEntry(writeChar, terminalColour)
+  let index = yPos * vgaWidth + xPos
+  vgaMem[index] = vga.vgaEntry(writeChar, terminalColour)
 
 proc terminalClear*() =
   for x in 0..<vgaWidth:
@@ -29,28 +32,29 @@ proc terminalScroll() =
   for y in 0..< (vgaHeight - 1):
     for x in 0..<vgaWidth:
       let xval = x * 2
-      let index1 = terminalBufferBaseAddress + (y * bufferWidthSkip + xval)
-      let index2 = terminalBufferBaseAddress +
-        ((y + 1) * bufferWidthSkip + xval)
-      cast[ptr int16](index1)[] = cast[ptr int16](index2)[]
+      let index1 = y * vgaWidth + x
+      let index2 = (y + 1) * vgaWidth + x
+      vgaMem[index1] = vgaMem[index2]
+  for x in 0..<vgaWidth: # Blank the "new" bottom line
+    terminalWriteAtPoint(' ', terminalColour, x, vgaHeight - 1)
 
 proc setTerminalColour(newColour: int) =
   terminalColour = newColour
 
 proc terminalWriteChar(writeChar: char) =
   if(writeChar == '\L'):
-    if(terminalRow < vgaHeight): inc(terminalRow)
-    #else: # If we are at the bottom of the screen then scroll the screen.
-      #terminalScroll()
+    if(terminalRow < vgaHeight - 1): inc(terminalRow)
+    else: # If we are at the bottom of the screen then scroll the screen.
+      terminalScroll()
     terminalColumn = 0
     return
   terminalWriteAtPoint(writeChar, terminalColour, terminalColumn, terminalRow)
   inc(terminalColumn)
   if(terminalColumn == vgaWidth):
     terminalColumn = 0
-    if(terminalRow < vgaHeight): inc(terminalRow)
-    #else: # If we are at the bottom of the screen then scroll the screen.
-      #terminalScroll()
+    if(terminalRow < vgaHeight - 1): inc(terminalRow)
+    else: # If we are at the bottom of the screen then scroll the screen.
+      terminalScroll()
 
 proc terminalWrite*(data: string) =
   for character in data:
@@ -62,11 +66,11 @@ proc terminalWrite*(data: char) =
 var parsedData = ['0','0','0','0','0','0','0','0','0','0']
 
 proc terminalWrite*(data: int) =
-  var input = data
-  var i = 0
-  if(input == 0):
+  if(data == 0):
     terminalWrite('0')
     return
+  var input = data
+  var i = 0
   if(input < 0):
     terminalWrite('-')
     input = input * -1
diff --git a/kernel/arch/i386/vga.nim b/kernel/arch/i386/vga.nim
index 3e062ab..13593cf 100644
--- a/kernel/arch/i386/vga.nim
+++ b/kernel/arch/i386/vga.nim
@@ -17,8 +17,10 @@ type
     lightBrown = 14,
     white = 15
 
+  VGADoubleByte* = distinct uint16
+
 proc vgaEntryColour*(fg: VGA_Colour, bg: VGA_Colour): int =
   result = ord(fg) or (ord(bg) shl 4)
 
-proc vgaEntry*(c: char, colour: int): int16 =
-  result = int16(int(c) or (colour shl 8))
+proc vgaEntry*(c: char, colour: int): VGADoubleByte =
+  result = (uint16(int(c) or (colour shl 8))).VGADoubleByte
diff --git a/kernel/kernel.nim b/kernel/kernel.nim
index 248c666..1f54d52 100644
--- a/kernel/kernel.nim
+++ b/kernel/kernel.nim
@@ -7,3 +7,6 @@ proc kernelMain() {.exportc: "kernel_main"}=
   terminalWrite(high(int))
   terminalWrite("\LMIN_INT:")
   terminalWrite(low(int32)+1)
+  for i in 0..22:
+    terminalWrite(i)
+    terminalWrite('\L')