Fix rendering of zero-width characters

Instead of rendering zero-width characters as full characters, they are
now properly rendered without advancing the cursor.

Because of performance limitations, this implementation only supports up
to 5 zero-width characters per cell. However, as a result of this
limitation there should not be any performance impact.

This fixes #1317, fixes #696 and closes #1318.

1 files changed, 40 insertions, 5 deletions

diff --git a/src/term/cell.rs b/src/term/cell.rs
index ef8509dc..e6fe980e 100644
--- a/src/term/cell.rs
+++ b/src/term/cell.rs
@@ -15,9 +15,12 @@ use ansi::{NamedColor, Color};
 use grid;
 use index::Column;
 
+// Maximum number of zerowidth characters which will be stored per cell.
+pub const MAX_ZEROWIDTH_CHARS: usize = 5;
+
 bitflags! {
     #[derive(Serialize, Deserialize)]
-    pub struct Flags: u32 {
+    pub struct Flags: u16 {
         const INVERSE           = 0b0_0000_0001;
         const BOLD              = 0b0_0000_0010;
         const ITALIC            = 0b0_0000_0100;
@@ -31,12 +34,18 @@ bitflags! {
     }
 }
 
+const fn default_extra() -> [char; MAX_ZEROWIDTH_CHARS] {
+    [' '; MAX_ZEROWIDTH_CHARS]
+}
+
 #[derive(Copy, Clone, Debug, Serialize, Deserialize, Eq, PartialEq)]
 pub struct Cell {
     pub c: char,
     pub fg: Color,
     pub bg: Color,
     pub flags: Flags,
+    #[serde(default="default_extra")]
+    pub extra: [char; MAX_ZEROWIDTH_CHARS],
 }
 
 impl Default for Cell {
@@ -65,7 +74,7 @@ impl LineLength for grid::Row<Cell> {
         }
 
         for (index, cell) in self[..].iter().rev().enumerate() {
-            if cell.c != ' ' {
+            if cell.c != ' ' || cell.extra[0] != ' ' {
                 length = Column(self.len() - index);
                 break;
             }
@@ -93,6 +102,7 @@ impl Cell {
 
     pub fn new(c: char, fg: Color, bg: Color) -> Cell {
         Cell {
+            extra: [' '; MAX_ZEROWIDTH_CHARS],
             c,
             bg,
             fg,
@@ -102,9 +112,10 @@ impl Cell {
 
     #[inline]
     pub fn is_empty(&self) -> bool {
-        self.c == ' ' &&
-            self.bg == Color::Named(NamedColor::Background) &&
-            !self.flags.intersects(Flags::INVERSE | Flags::UNDERLINE)
+        self.c == ' '
+            && self.extra[0] == ' '
+            && self.bg == Color::Named(NamedColor::Background)
+            && !self.flags.intersects(Flags::INVERSE | Flags::UNDERLINE)
     }
 
     #[inline]
@@ -112,6 +123,30 @@ impl Cell {
         // memcpy template to self
         *self = *template;
     }
+
+    #[inline]
+    pub fn chars(&self) -> [char; MAX_ZEROWIDTH_CHARS + 1] {
+        unsafe {
+            let mut chars = [std::mem::uninitialized(); MAX_ZEROWIDTH_CHARS + 1];
+            std::ptr::write(&mut chars[0], self.c);
+            std::ptr::copy_nonoverlapping(
+                self.extra.as_ptr(),
+                chars.as_mut_ptr().offset(1),
+                self.extra.len(),
+            );
+            chars
+        }
+    }
+
+    #[inline]
+    pub fn push_extra(&mut self, c: char) {
+        for elem in self.extra.iter_mut() {
+            if elem == &' ' {
+                *elem = c;
+                break;
+            }
+        }
+    }
 }
 
 #[cfg(test)]