From 66a80baeed5ad02cfde0091031ab6b6d76944d46 Mon Sep 17 00:00:00 2001
From: Nathan Vegdahl <cessen@cessen.com>
Date: Sun, 31 Dec 2017 18:51:02 -0800
Subject: [PATCH] Doing screen buffering to eliminate flicker.

At the moment, it's brain-dead and really slow.
---
 src/term_ui/mod.rs    |  1 +
 src/term_ui/screen.rs | 90 +++++++++++++++++++++++++++++++++++--------
 2 files changed, 76 insertions(+), 15 deletions(-)

diff --git a/src/term_ui/mod.rs b/src/term_ui/mod.rs
index d74c1d7..7a988a7 100644
--- a/src/term_ui/mod.rs
+++ b/src/term_ui/mod.rs
@@ -52,6 +52,7 @@ macro_rules! ui_loop {
                 $term_ui.width = w as usize;
                 $term_ui.height = h as usize;
                 $term_ui.editor.update_dim($term_ui.height - 1, $term_ui.width);
+                $term_ui.screen.resize(w as usize, h as usize);
             }
 
             if stop || $term_ui.quit {
diff --git a/src/term_ui/screen.rs b/src/term_ui/screen.rs
index 0d36b6e..c4ccf62 100644
--- a/src/term_ui/screen.rs
+++ b/src/term_ui/screen.rs
@@ -1,7 +1,10 @@
+use std;
 use std::cell::RefCell;
 use std::io;
 use std::io::Write;
 
+use unicode_width::UnicodeWidthStr;
+use unicode_segmentation::UnicodeSegmentation;
 use termion;
 use termion::screen::AlternateScreen;
 use termion::color;
@@ -9,29 +12,81 @@ use termion::raw::{IntoRawMode, RawTerminal};
 
 pub(crate) struct Screen {
     out: RefCell<AlternateScreen<RawTerminal<io::Stdout>>>,
+    buf: RefCell<Vec<Option<String>>>,
+    w: usize,
+    h: usize,
 }
 
 impl Screen {
     pub(crate) fn new() -> Self {
+        let (w, h) = termion::terminal_size().unwrap();
+        let buf = std::iter::repeat(Some(format!(
+            "{}{} ",
+            color::Fg(color::Black),
+            color::Bg(color::Black)
+        ))).take(w as usize * h as usize)
+            .collect();
         Screen {
             out: RefCell::new(AlternateScreen::from(io::stdout().into_raw_mode().unwrap())),
+            buf: RefCell::new(buf),
+            w: w as usize,
+            h: h as usize,
         }
     }
 
     pub(crate) fn clear(&self) {
-        write!(
-            self.out.borrow_mut(),
-            "{}{}",
-            color::Bg(color::Black),
-            termion::clear::All
-        ).unwrap();
+        for cell in self.buf.borrow_mut().iter_mut() {
+            match *cell {
+                Some(ref mut text) => {
+                    text.clear();
+                    text.push_str(&format!(
+                        "{}{} ",
+                        color::Fg(color::Black),
+                        color::Bg(color::Black)
+                    ));
+                }
+                _ => {
+                    *cell = Some(format!(
+                        "{}{} ",
+                        color::Fg(color::Black),
+                        color::Bg(color::Black)
+                    ));
+                }
+            }
+        }
+    }
+
+    pub(crate) fn resize(&mut self, w: usize, h: usize) {
+        self.w = w;
+        self.h = h;
+        self.buf.borrow_mut().resize(
+            w * h,
+            Some(format!(
+                "{}{} ",
+                color::Fg(color::Black),
+                color::Bg(color::Black)
+            )),
+        );
     }
 
     pub(crate) fn present(&self) {
+        let buf = self.buf.borrow();
+        for y in 0..self.h {
+            for x in 0..self.w {
+                if let Some(ref cell) = buf[y * self.w + x] {
+                    write!(
+                        self.out.borrow_mut(),
+                        "{}{}",
+                        termion::cursor::Goto((x + 1) as u16, (y + 1) as u16),
+                        cell
+                    ).unwrap();
+                }
+            }
+        }
         self.out.borrow_mut().flush().unwrap();
     }
 
-    pub(crate) fn draw<C1: color::Color, C2: color::Color>(
+    pub(crate) fn draw<C1: color::Color + Copy, C2: color::Color + Copy>(
         &self,
         x: usize,
         y: usize,
@@ -39,14 +94,19 @@ impl Screen {
         fg: C1,
         bg: C2,
     ) {
-        write!(
-            self.out.borrow_mut(),
-            "{}{}{}{}",
-            termion::cursor::Goto((x + 1) as u16, (y + 1) as u16),
-            color::Fg(fg),
-            color::Bg(bg),
-            text
-        ).unwrap();
+        let mut buf = self.buf.borrow_mut();
+        let mut x = x;
+        for g in UnicodeSegmentation::graphemes(text, true) {
+            let width = UnicodeWidthStr::width(g);
+            if width > 0 {
+                buf[y * self.w + x] = Some(format!("{}{}{}", color::Fg(fg), color::Bg(bg), g));
+                x += 1;
+                for _ in 0..(width - 1) {
+                    buf[y * self.w + x] = None;
+                    x += 1;
+                }
+            }
+        }
     }
 
     pub(crate) fn hide_cursor(&self) {