Fix sharp corners for rectangles with StrokeKind != Inside

Author: emilk

crates/egui_demo_lib/src/demo/tests/tessellation_test.rs

@@ -93,6 +93,19 @@ impl TessellationTest {
                 )
                 .with_blur_width(5.0),
             ),
+            (
+                "Additive rectangle",
+                RectShape::new(
+                    sized([24.0, 12.0]),
+                    0.0,
+                    egui::Color32::LIGHT_RED.additive().linear_multiply(0.025),
+                    (
+                        1.0,
+                        egui::Color32::LIGHT_BLUE.additive().linear_multiply(0.1),
+                    ),
+                    StrokeKind::Outside,
+                ),
+            ),
         ];
 
         for (_name, shape) in &mut shapes {

crates/egui_demo_lib/tests/snapshots/rendering_test/dpi_1.00.png

@@ -1885,19 +1885,27 @@ impl Tessellator {
 
             let extra_cr_tweak = 0.4; // Otherwise is doesn't _feels_  enough.
 
-            if 0.0 < original_cr.nw {
+            if original_cr.nw == 0.0 {
+                corner_radius.nw = 0.0;
+            } else {
                 corner_radius.nw += extra_cr_tweak;
                 corner_radius.nw = corner_radius.nw.at_least(min_outside_cr);
             }
-            if 0.0 < original_cr.ne {
+            if original_cr.ne == 0.0 {
+                corner_radius.ne = 0.0;
+            } else {
                 corner_radius.ne += extra_cr_tweak;
                 corner_radius.ne = corner_radius.ne.at_least(min_outside_cr);
             }
-            if 0.0 < original_cr.sw {
+            if original_cr.sw == 0.0 {
+                corner_radius.sw = 0.0;
+            } else {
                 corner_radius.sw += extra_cr_tweak;
                 corner_radius.sw = corner_radius.sw.at_least(min_outside_cr);
             }
-            if 0.0 < original_cr.se {
+            if original_cr.se == 0.0 {
+                corner_radius.se = 0.0;
+            } else {
                 corner_radius.se += extra_cr_tweak;
                 corner_radius.se = corner_radius.se.at_least(min_outside_cr);
             }