Merge pull request #77 from notgull/early-div-zero

bugfix: Panic if a line height of zero is passed into Buffer

src/buffer.rs

@@ -306,6 +306,8 @@ pub struct Buffer<'a> {
 impl<'a> Buffer<'a> {
     /// Create a new [`Buffer`] with the provided [`FontSystem`] and [`Metrics`]
     pub fn new(font_system: &'a FontSystem, metrics: Metrics) -> Self {
+        assert_ne!(metrics.line_height, 0, "line height cannot be 0");
+
         let mut buffer = Self {
             font_system,
             lines: Vec::new(),
@@ -491,6 +493,7 @@ impl<'a> Buffer<'a> {
     /// Set the current [`Metrics`]
     pub fn set_metrics(&mut self, metrics: Metrics) {
         if metrics != self.metrics {
+            assert_ne!(metrics.font_size, 0, "font size cannot be 0");
             self.metrics = metrics;
             self.relayout();
             self.shape_until_scroll();