We now store character widths in TextBlocks.

This is the first step towards supporting proportional fonts
and tabs characters.

src/buffer/text_block.rs

@@ -2,31 +2,49 @@
 
 use std::mem;
 use std::fmt;
-use string_utils::char_pos_to_byte_pos;
+use string_utils::{char_pos_to_byte_pos, char_count};
 
 /// A block of text, contiguous in memory
 pub struct TextBlock {
+    // The actual text data, in utf8
     pub data: Vec<u8>,
+    
+    // The visual width of each printable character.
+    // Characters with variable width (e.g. tab characters)
+    // have width None.
+    pub widths: Vec<Option<u8>>,
 }
 
 impl TextBlock {
     /// Create a new empty text block.
     pub fn new() -> TextBlock {
         TextBlock {
-            data: Vec::<u8>::new()
+            data: Vec::<u8>::new(),
+            widths: Vec::<Option<u8>>::new(),
         }
     }
     
     /// Create a new text block with the contents of 'text'.
     pub fn new_from_str(text: &str) -> TextBlock {
         let mut tb = TextBlock {
-            data: Vec::<u8>::with_capacity(text.len())
+            data: Vec::<u8>::with_capacity(text.len()),
+            widths: Vec::<Option<u8>>::with_capacity(text.len()),
         };
         
         for b in text.bytes() {
             tb.data.push(b);
         }
         
+        // TODO: handle fonts
+        for c in text.chars() {
+            if c == '\t' {
+                tb.widths.push(None);
+            }
+            else {
+                tb.widths.push(Some(1));
+            }
+        }
+        
         return tb;
     }
     
@@ -35,8 +53,35 @@ impl TextBlock {
         self.data.len()
     }
     
+    /// Returns the total width of text block sans-variable-width characters
+    pub fn total_non_variable_width(&self) -> uint {
+        let mut width: uint = 0;
+        
+        for w in self.widths.iter() {
+            if let &Some(ww) = w {
+                width += ww as uint;
+            }
+        }
+        
+        return width;
+    }
+    
+    /// Returns the number of variable-width chars in the text block
+    pub fn variable_width_chars(&self) -> uint {
+        let mut count: uint = 0;
+        
+        for w in self.widths.iter() {
+            if let &None = w {
+                count += 1;
+            }
+        }
+        
+        return count;
+    }
+    
     /// Insert 'text' at char position 'pos'.
     pub fn insert_text(&mut self, text: &str, pos: uint) {
+        //====== TEXT DATA ======
         // Find insertion position in bytes
         let byte_pos = char_pos_to_byte_pos(self.as_str(), pos);
 
@@ -59,6 +104,33 @@ impl TextBlock {
             self.data[i] = b;
             i += 1
         }
+        
+        //====== WIDTHS ======
+        // Grow widths size
+        let cc = char_count(text);
+        self.widths.grow(cc, None);
+        
+        // Move old widths forward
+        from = self.widths.len() - cc;
+        to = self.widths.len();
+        while from > pos {
+            from -= 1;
+            to -= 1;
+            
+            self.widths[to] = self.widths[from];
+        }
+        
+        // Copy new widths in
+        i = pos;
+        for c in text.chars() {
+            if c == '\t' {
+                self.widths[i] = None;
+            }
+            else {
+                self.widths[i] = Some(1);
+            }
+            i += 1
+        }
     }
     
     /// Remove the text between char positions 'pos_a' and 'pos_b'.
@@ -68,6 +140,7 @@ impl TextBlock {
             panic!("TextBlock::remove_text(): pos_a must be less than or equal to pos_b.");
         }
         
+        //====== TEXT DATA ======
         // Find removal positions in bytes
         let byte_pos_a = char_pos_to_byte_pos(self.as_str(), pos_a);
         let byte_pos_b = char_pos_to_byte_pos(self.as_str(), pos_b);
@@ -83,8 +156,22 @@ impl TextBlock {
         }
         
         // Remove data from the end
-        let final_size = self.data.len() + byte_pos_a - byte_pos_b;
-        self.data.truncate(final_size);
+        let final_data_size = self.data.len() + byte_pos_a - byte_pos_b;
+        self.data.truncate(final_data_size);
+        
+        //====== WIDTHS ======
+        from = pos_b;
+        to = pos_a;
+        while from < self.widths.len() {
+            self.widths[to] = self.widths[from];
+            
+            from += 1;
+            to += 1;
+        }
+        
+        // Remove data from end
+        let final_widths_size = self.widths.len() + pos_a - pos_b;
+        self.data.truncate(final_widths_size);
     }
     
     /// Returns an immutable string slice into the text block's memory

todo.md

@@ -1,4 +1,6 @@
-- Proper handling of tab characters
+- Proper handling of non-uniform-width characters.  Specifically, this needs
+  to address tabs.  But it should be done to handle the general case anyway,
+  since that's unlikely to be more complex and will future-proof things.
 - Line number display
 - Editor info display (filename, current line/column, indentation style, etc.)
 - File opening by entering path