Prevent font_size_modifier from sinking too low (#994)

This replaces the `font_size_modifier` stored on the `Term` struct with a `font_size` field.

With this change it is not necessary anymore to calculate the new font size from a delta but the current font size is always stored directly on the `Term` struct.

As a result of this it is now possible to increase the font size by more than 127 steps at runtime. It also limits the minimum font size to 1, so issues with the `font_size_modifier` dropping far below font size 1 are resolved with this change.

This fixes #955.

5 files changed, 29 insertions, 32 deletions

diff --git a/font/src/lib.rs b/font/src/lib.rs
index ad1f4f80..330ed362 100644
--- a/font/src/lib.rs
+++ b/font/src/lib.rs
@@ -166,7 +166,7 @@ impl Hash for GlyphKey {
 }
 
 /// Font size stored as integer
-#[derive(Debug, Copy, Clone, Hash, PartialEq, Eq)]
+#[derive(Debug, Copy, Clone, Hash, PartialEq, Eq, PartialOrd, Ord)]
 pub struct Size(i16);
 
 impl Size {
diff --git a/src/config.rs b/src/config.rs
index e7ab3403..2a2ba6db 100644
--- a/src/config.rs
+++ b/src/config.rs
@@ -1467,13 +1467,9 @@ impl Font {
     }
 
     /// Get a font clone with a size modification
-    pub fn with_size_delta(self, delta: f32) -> Font {
-        let mut new_size = self.size.as_f32_pts() + delta;
-        if new_size < 1.0 {
-            new_size = 1.0;
-        }
+    pub fn with_size(self, size: Size) -> Font {
         Font {
-            size : Size::new(new_size),
+            size,
             .. self
         }
     }
diff --git a/src/display.rs b/src/display.rs
index 89403194..5ca2abb5 100644
--- a/src/display.rs
+++ b/src/display.rs
@@ -96,7 +96,7 @@ pub struct Display {
     rx: mpsc::Receiver<(u32, u32)>,
     tx: mpsc::Sender<(u32, u32)>,
     meter: Meter,
-    font_size_modifier: i8,
+    font_size: font::Size,
     size_info: SizeInfo,
     last_background_color: Rgb,
 }
@@ -150,7 +150,7 @@ impl Display {
         let mut renderer = QuadRenderer::new(config, viewport_size)?;
 
         let (glyph_cache, cell_width, cell_height) =
-            Self::new_glyph_cache(&window, &mut renderer, config, 0)?;
+            Self::new_glyph_cache(&window, &mut renderer, config)?;
 
 
         let dimensions = options.dimensions()
@@ -205,17 +205,16 @@ impl Display {
             tx: tx,
             rx: rx,
             meter: Meter::new(),
-            font_size_modifier: 0,
+            font_size: font::Size::new(0.),
             size_info: size_info,
             last_background_color: background_color,
         })
     }
 
-    fn new_glyph_cache(window : &Window, renderer : &mut QuadRenderer,
-                       config: &Config, font_size_delta: i8)
+    fn new_glyph_cache(window : &Window, renderer : &mut QuadRenderer, config: &Config)
         -> Result<(GlyphCache, f32, f32), Error>
     {
-        let font = config.font().clone().with_size_delta(font_size_delta as f32);
+        let font = config.font().clone();
         let dpr = window.hidpi_factor();
         let rasterizer = font::Rasterizer::new(dpr, config.use_thin_strokes())?;
 
@@ -245,10 +244,11 @@ impl Display {
         Ok((glyph_cache, cell_width as f32, cell_height as f32))
     }
 
-    pub fn update_glyph_cache(&mut self, config: &Config, font_size_delta: i8) {
+    pub fn update_glyph_cache(&mut self, config: &Config) {
         let cache = &mut self.glyph_cache;
+        let size = self.font_size;
         self.renderer.with_loader(|mut api| {
-            let _ = cache.update_font_size(config.font(), font_size_delta, &mut api);
+            let _ = cache.update_font_size(config.font(), size, &mut api);
         });
 
         let metrics = cache.font_metrics();
@@ -282,11 +282,10 @@ impl Display {
             new_size = Some(sz);
         }
 
-        if terminal.font_size_modifier != self.font_size_modifier {
-            // Font size modification detected
-
-            self.font_size_modifier = terminal.font_size_modifier;
-            self.update_glyph_cache(config, terminal.font_size_modifier);
+        // Font size modification detected
+        if terminal.font_size != self.font_size {
+            self.font_size = terminal.font_size;
+            self.update_glyph_cache(config);
 
             if new_size == None {
                 // Force a resize to refresh things
diff --git a/src/renderer/mod.rs b/src/renderer/mod.rs
index 318a1835..9d52b024 100644
--- a/src/renderer/mod.rs
+++ b/src/renderer/mod.rs
@@ -295,7 +295,7 @@ impl GlyphCache {
     pub fn update_font_size<L: LoadGlyph>(
         &mut self,
         font: &config::Font,
-        delta: i8,
+        size: font::Size,
         loader: &mut L
     ) -> Result<(), font::Error> {
         // Clear currently cached data in both GL and the registry
@@ -303,8 +303,8 @@ impl GlyphCache {
         self.cache = HashMap::default();
 
         // Recompute font keys
-        let font = font.to_owned().with_size_delta(delta as _);
-        println!("{:?}", font.size);
+        let font = font.to_owned().with_size(size);
+        info!("Font size changed: {:?}", font.size);
         let (regular, bold, italic) = Self::compute_font_keys(&font, &mut self.rasterizer)?;
         self.rasterizer.get_glyph(&GlyphKey { font_key: regular, c: 'm', size: font.size() })?;
         let metrics = self.rasterizer.metrics(regular)?;
diff --git a/src/term/mod.rs b/src/term/mod.rs
index e43ea7b6..7e6ff1e0 100644
--- a/src/term/mod.rs
+++ b/src/term/mod.rs
@@ -22,7 +22,7 @@ use std::time::{Duration, Instant};
 use arraydeque::ArrayDeque;
 use unicode_width::UnicodeWidthChar;
 
-use font;
+use font::{self, Size};
 use ansi::{self, Color, NamedColor, Attr, Handler, CharsetIndex, StandardCharset, CursorStyle};
 use grid::{BidirectionalIterator, Grid, ClearRegion, ToRange, Indexed};
 use index::{self, Point, Column, Line, Linear, IndexRange, Contains, RangeInclusive};
@@ -685,8 +685,9 @@ pub struct Term {
     /// Scroll region
     scroll_region: Range<Line>,
 
-    /// Font size modifier
-    pub font_size_modifier: i8,
+    /// Font size
+    pub font_size: Size,
+    original_font_size: Size,
 
     /// Size
     size_info: SizeInfo,
@@ -814,7 +815,8 @@ impl Term {
             grid: grid,
             alt_grid: alt,
             alt: false,
-            font_size_modifier: 0,
+            font_size: config.font().size(),
+            original_font_size: config.font().size(),
             active_charset: Default::default(),
             cursor: Default::default(),
             cursor_save: Default::default(),
@@ -834,14 +836,14 @@ impl Term {
     }
 
     pub fn change_font_size(&mut self, delta: i8) {
-        if let Some(sum) = self.font_size_modifier.checked_add(delta) {
-            self.font_size_modifier = sum;
-            self.dirty = true;
-        }
+        // Saturating addition with minimum font size 1
+        let new_size = self.font_size + Size::new(delta as f32);
+        self.font_size = max(new_size, Size::new(1.));
+        self.dirty = true;
     }
 
     pub fn reset_font_size(&mut self) {
-        self.font_size_modifier = 0;
+        self.font_size = self.original_font_size;
         self.dirty = true;
     }