scrolling now uses the terminal scroll feature when possible

it doesn't redraw the newly blank lines in that case though, so it's broken, but that can come next

Force-Push: yes
Change-Id: I52c90249852331e5f9bbcdee4d645ee33e4c671a

2 files changed, 51 insertions, 9 deletions

diff --git a/src/main.rs b/src/main.rs
index 2f93a2e..b94b274 100644
--- a/src/main.rs
+++ b/src/main.rs
@@ -161,7 +161,8 @@ impl Ivy {
       terminal.stdout.write_all("\n~".as_bytes()).await?;
     }
 
-    terminal.stdout.write_all("\n        status goes here".as_bytes()).await?;
+    terminal.do_cursor_position(0, height).await?;
+    terminal.stdout.write_all("        status goes here".as_bytes()).await?;
 
     let window = self.window.read().await;
     terminal.do_cursor_position(*window.cursor_column.read().await,
@@ -385,9 +386,15 @@ impl Ivy {
     }
 
     let new_scroll_top = *self.window.read().await.scroll_top.read().await;
-    if old_scroll_top != new_scroll_top {
-      self.terminal.write().await.clear().await?;
-      self.draw().await?;
+    let height = *self.terminal.read().await.height.read().await - 1;
+    if new_scroll_top != old_scroll_top {
+      let difference = new_scroll_top as isize - old_scroll_top as isize;
+      if (difference.abs() as usize) < height {
+        self.terminal.write().await.scroll(difference).await?;
+      } else {
+        self.terminal.write().await.clear().await?;
+        self.draw().await?;
+      }
     }
 
     Ok(())
diff --git a/src/terminal.rs b/src/terminal.rs
index 9188c43..1ba2b01 100644
--- a/src/terminal.rs
+++ b/src/terminal.rs
@@ -81,10 +81,18 @@ impl Terminal {
     *self.width.write().await = width.try_into().unwrap();
     *self.height.write().await = height.try_into().unwrap();
 
+    self.set_scroll_region(0, height - 1).await?;
+
     Ok(())
   }
 
   pub async fn zap_full_screen(&mut self) -> Result<()> {
+    let (width, height) = self.do_report_size().await?;
+    *self.width.write().await = width.try_into().unwrap();
+    *self.height.write().await = height.try_into().unwrap();
+
+    self.set_scroll_region(0, height).await?;
+
     self.do_end_alternate_screen().await?;
     self.stdout.flush().await?;
 
@@ -113,7 +121,7 @@ impl Terminal {
   }
 
   pub async fn read_report(&mut self, escape_type: EscapeType)
-      -> Result<(char, Vec<u64>)>
+      -> Result<(char, Vec<usize>)>
   {
     let mut expected = escape_type.intro();
 
@@ -126,7 +134,7 @@ impl Terminal {
 
     let mut values = Vec::new();
 
-    let mut number: u64 = 0;
+    let mut number: usize = 0;
     let mut in_number = false;
     let mut after_semicolon = false;
 
@@ -140,9 +148,11 @@ impl Terminal {
         if c.is_ascii_digit() {
           if in_number {
             number = number * 10
-                     + <u32 as Into<u64>>::into(c.to_digit(10).unwrap());
+                     + <u32 as TryInto<usize>>::try_into(
+                           c.to_digit(10).unwrap()).unwrap();
           } else {
-            number = c.to_digit(10).unwrap().into();
+            number = <u32 as TryInto<usize>>::try_into(
+                         c.to_digit(10).unwrap()).unwrap();
 
             in_number = true;
             after_semicolon = false;
@@ -195,7 +205,7 @@ impl Terminal {
   }
 
   // dtterm? xterm
-  pub async fn do_report_size(&mut self) -> Result<(u64, u64)> {
+  pub async fn do_report_size(&mut self) -> Result<(usize, usize)> {
     self.do_escape(EscapeType::CSI, "t", &[18]).await?;
     self.stdout.flush().await?;
     let (code, values) = self.read_report(EscapeType::CSI).await?;
@@ -210,6 +220,31 @@ impl Terminal {
   pub async fn clear(&mut self) -> Result<()> {
     self.do_escape(EscapeType::CSI, "J", &[2]).await
   }
+
+  // vt420, ECMA-48
+  pub async fn scroll_up(&mut self, distance: usize) -> Result<()> {
+    self.do_escape(EscapeType::CSI, "S", &[distance]).await
+  }
+
+  // vt420, ECMA-48
+  pub async fn scroll_down(&mut self, distance: usize) -> Result<()> {
+    self.do_escape(EscapeType::CSI, "T", &[distance]).await
+  }
+
+  pub async fn scroll(&mut self, distance_up: isize) -> Result<()> {
+    if distance_up >= 0 {
+      self.scroll_up(distance_up as usize).await
+    } else {
+      self.scroll_down(-distance_up as usize).await
+    }
+  }
+
+  // vt100
+  pub async fn set_scroll_region(&mut self, top: usize, bottom: usize)
+      -> Result<()>
+  {
+    self.do_escape(EscapeType::CSI, "r", &[top, bottom]).await
+  }
 }