Better handle additive colors in plots (#3387)

emilk · Sep 25, 2023 · 8bf0055 · 8bf0055
1 parent fdd493d
commit 8bf0055
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Showing 3 changed files with 23 additions and 3 deletions.
diff --git a/crates/ecolor/src/color32.rs b/crates/ecolor/src/color32.rs
@@ -155,6 +155,12 @@ impl Color32 {
         Self([r, g, b, 0])
     }
 
+    /// Is the alpha=0 ?
+    #[inline(always)]
+    pub fn is_additive(self) -> bool {
+        self.a() == 0
+    }
+
     /// Premultiplied RGBA
     #[inline(always)]
     pub const fn to_array(&self) -> [u8; 4] {

diff --git a/crates/ecolor/src/rgba.rs b/crates/ecolor/src/rgba.rs
@@ -122,6 +122,12 @@ impl Rgba {
         Self([r, g, b, 0.0])
     }
 
+    /// Is the alpha=0 ?
+    #[inline(always)]
+    pub fn is_additive(self) -> bool {
+        self.a() == 0.0
+    }
+
     /// Multiply with e.g. 0.5 to make us half transparent
     #[inline(always)]
     pub fn multiply(self, alpha: f32) -> Self {

diff --git a/crates/egui_plot/src/items/rect_elem.rs b/crates/egui_plot/src/items/rect_elem.rs
@@ -58,8 +58,16 @@ pub(super) trait RectElement {
 
 pub(super) fn highlighted_color(mut stroke: Stroke, fill: Color32) -> (Stroke, Color32) {
     stroke.width *= 2.0;
-    let fill = Rgba::from(fill);
-    let fill_alpha = (2.0 * fill.a()).at_most(1.0);
-    let fill = fill.to_opaque().multiply(fill_alpha);
+
+    let mut fill = Rgba::from(fill);
+    if fill.is_additive() {
+        // Make slightly brighter
+        fill = 1.3 * fill;
+    } else {
+        // Make more opaque:
+        let fill_alpha = (2.0 * fill.a()).at_most(1.0);
+        fill = fill.to_opaque().multiply(fill_alpha);
+    }
+
     (stroke, fill.into())
 }