Tesselator: ignore zero-sized clip rects

Improves https://github.com/emilk/egui/issues/328

egui/src/layout.rs

@@ -333,7 +333,7 @@ impl Layout {
 impl Layout {
     pub fn align_size_within_rect(&self, size: Vec2, outer: Rect) -> Rect {
         debug_assert!(size.x >= 0.0 && size.y >= 0.0);
-        debug_assert!(outer.is_non_negative());
+        debug_assert!(!outer.is_negative());
         self.align2().align_size_within_rect(size, outer)
     }
 
@@ -571,7 +571,7 @@ impl Layout {
     /// Apply justify (fill width/height) and/or alignment after calling `next_space`.
     pub(crate) fn justify_and_align(&self, frame: Rect, mut child_size: Vec2) -> Rect {
         debug_assert!(child_size.x >= 0.0 && child_size.y >= 0.0);
-        debug_assert!(frame.is_non_negative());
+        debug_assert!(!frame.is_negative());
 
         if self.horizontal_justify() {
             child_size.x = child_size.x.at_least(frame.width()); // fill full width

emath/src/rect.rs

@@ -297,16 +297,21 @@ impl Rect {
         self.max.x < self.min.x || self.max.y < self.min.y
     }
 
-    /// `max.x < min.x` or `max.y < min.y`.
+    /// `width < 0 || height < 0`
     #[inline(always)]
     pub fn is_negative(&self) -> bool {
         self.max.x < self.min.x || self.max.y < self.min.y
     }
 
-    /// `min.x <= max.x && min.y <= max.y`.
-    #[inline(always)]
+    #[deprecated = "Use !is_negative() instead"]
     pub fn is_non_negative(&self) -> bool {
-        self.min.x <= self.max.x && self.min.y <= self.max.y
+        !self.is_negative()
+    }
+
+    /// `width > 0 && height > 0`
+    #[inline(always)]
+    pub fn is_positive(&self) -> bool {
+        self.min.x < self.max.x && self.min.y < self.max.y
     }
 
     /// True if all members are also finite.

epaint/src/tessellator.rs

@@ -742,7 +742,7 @@ pub fn tessellate_shapes(
     let mut clipped_meshes: Vec<ClippedMesh> = Vec::default();
 
     for ClippedShape(clip_rect, shape) in shapes {
-        if !clip_rect.is_non_negative() {
+        if !clip_rect.is_positive() {
             continue; // skip empty clip rectangles
         }