From 80cbe0900d773bef1a2022022933f7b7498021eb Mon Sep 17 00:00:00 2001
From: churl <tobi@urpost.de>
Date: Tue, 17 May 2022 18:38:52 +0200
Subject: [PATCH] BufferedCGA refactoring

---
 c_os/devices/BufferedCGA.cc  |  4 ++--
 c_os/lib/ScrollbackBuffer.cc | 18 +++---------------
 c_os/lib/ScrollbackBuffer.h  | 10 +++++-----
 3 files changed, 10 insertions(+), 22 deletions(-)

diff --git a/c_os/devices/BufferedCGA.cc b/c_os/devices/BufferedCGA.cc
index e65f904..b358c9c 100755
--- a/c_os/devices/BufferedCGA.cc
+++ b/c_os/devices/BufferedCGA.cc
@@ -13,7 +13,7 @@ void BufferedCGA::display_scrollback() {
     if (this->initialized) {
         if (this->scrollback == 0) {
             // Use pagebuffer
-            this->scrollback_buffer->copy_from_pagebuffer((cga_page_t*)CGA_START);
+            this->scrollback_buffer->save_screen((cga_page_t*)CGA_START);
         } else {
             // Use scrollback
             this->scrollback_buffer->get((cga_line_t*)CGA_START, this->scrollback - 1);
@@ -60,7 +60,7 @@ void BufferedCGA::scroll_page_backward() {
 
         // If this is the first scrollback we have to save the current screen content
         if (this->scrollback == 0) {
-            this->scrollback_buffer->copy_to_pagebuffer((cga_page_t*)CGA_START);
+            this->scrollback_buffer->restore_screen((cga_page_t*)CGA_START);
         }
 
         // current_page can be equal to scrollback_buffer->pages
diff --git a/c_os/lib/ScrollbackBuffer.cc b/c_os/lib/ScrollbackBuffer.cc
index 90b9492..bddc878 100755
--- a/c_os/lib/ScrollbackBuffer.cc
+++ b/c_os/lib/ScrollbackBuffer.cc
@@ -14,22 +14,10 @@ void ScrollbackBuffer::get(CGA::cga_line_t* destination, unsigned char page) con
         return;
     }
 
-    // We reverse the pagenumber so page 0 is always the current page
-    // (The last written line is always before curent_line
-    //  so we need to take the last page if we want the newest lines)
+    // We reverse the pagenumber so page 0 is always the newest page
     unsigned char rpage = this->pages - page - 1;
 
     // Copy linewise because page may wrap around buffer borders
-
-    // Pageheight: 4, Pages: 2      |  page = 0 => rpage = 2 - 0 - 1 = 1
-    // LINE 0                       |   - line = 0 => wrapline = (5 + 1 * 4 + 0) % 8 = 1
-    // LINE 1                       |   - [...]
-    // LINE 2                       |   - line = 3 => wrapline = (5 + 1 * 4 + 3) % 8 = 4
-    // LINE 3                       |
-    // LINE 4                       |  page = 1 => rpage = 2 - 1 - 1 = 0
-    // LINE 5 - current_linenumber  |   - line = 0 => wrapline = (5 + 0 * 4 + 0) % 8 = 5
-    // LINE 6                       |   - [...]
-    // LINE 7                       |   - line = 3 => wrapline = (5 + 0 * 4 + 3) % 8 = 0
     unsigned int wrapline;
     for (unsigned int line = 0; line < (this->rows / this->pages); ++line) {
         wrapline = (this->pos + rpage * (this->rows / this->pages) + line) % this->rows;
@@ -37,11 +25,11 @@ void ScrollbackBuffer::get(CGA::cga_line_t* destination, unsigned char page) con
     }
 }
 
-void ScrollbackBuffer::copy_from_pagebuffer(CGA::cga_page_t* destination) const {
+void ScrollbackBuffer::save_screen(CGA::cga_page_t* destination) const {
     mmem::memcpy<CGA::cga_page_t>(destination, this->pagebuffer);
 }
 
-void ScrollbackBuffer::copy_to_pagebuffer(CGA::cga_page_t* source) {
+void ScrollbackBuffer::restore_screen(CGA::cga_page_t* source) {
     mmem::memcpy<CGA::cga_page_t>(this->pagebuffer, source);
 }
 
diff --git a/c_os/lib/ScrollbackBuffer.h b/c_os/lib/ScrollbackBuffer.h
index 621a4f4..16810ad 100755
--- a/c_os/lib/ScrollbackBuffer.h
+++ b/c_os/lib/ScrollbackBuffer.h
@@ -23,9 +23,9 @@ public:
 
     ScrollbackBuffer(unsigned char rows, unsigned char pages)
       : pos(0), pages(pages), rows(rows * pages) {
-        this->buffer = new CGA::cga_page_t[pages];
-        this->pagebuffer = new CGA::cga_page_t;
-        this->clear();  // Null out the buffer so no crap gets displayed
+        this->buffer = new CGA::cga_page_t[pages];  // Allocate with new because it's quite large,
+        this->pagebuffer = new CGA::cga_page_t;     // also I wanted to use the new memory manager.
+        this->clear();                              // Null out the buffer so no crap gets displayed.
     }
     ~ScrollbackBuffer() {
         delete[] this->buffer;
@@ -34,8 +34,8 @@ public:
 
     void put(CGA::cga_line_t* line);
     void get(CGA::cga_line_t* destination, unsigned char page) const;
-    void copy_from_pagebuffer(CGA::cga_page_t* destination) const;
-    void copy_to_pagebuffer(CGA::cga_page_t* source);
+    void save_screen(CGA::cga_page_t* destination) const;  // Do not lose video memory when scrolling
+    void restore_screen(CGA::cga_page_t* source);
     void clear();
 };