From 7db6101aeada8a713cbfea9a8fc1b400eab2939e Mon Sep 17 00:00:00 2001
From: Robbert van der Helm <mail@robbertvanderhelm.nl>
Date: Tue, 29 Mar 2022 17:00:00 +0200
Subject: [PATCH] Only resize when clicking on the triangle part

---
 nih_plug_vizia/src/widgets/resize_handle.rs | 56 +++++++++++++++++----
 1 file changed, 47 insertions(+), 9 deletions(-)

diff --git a/nih_plug_vizia/src/widgets/resize_handle.rs b/nih_plug_vizia/src/widgets/resize_handle.rs
index bffd84a1..fd5123ec 100644
--- a/nih_plug_vizia/src/widgets/resize_handle.rs
+++ b/nih_plug_vizia/src/widgets/resize_handle.rs
@@ -39,15 +39,26 @@ impl View for ResizeHandle {
         if let Some(window_event) = event.message.downcast() {
             match *window_event {
                 WindowEvent::MouseDown(MouseButton::Left) => {
-                    cx.capture();
-                    cx.current.set_active(cx, true);
+                    // The handle is a triangle, so we should also interac twith it as if it was a
+                    // triangle
+                    if intersects_triangle(
+                        cx.cache.get_bounds(cx.current),
+                        (cx.mouse.cursorx, cx.mouse.cursory),
+                    ) {
+                        cx.capture();
+                        cx.current.set_active(cx, true);
 
-                    self.drag_active = true;
-                    self.start_scale_factor = cx.user_scale_factor;
-                    self.start_physical_coordinates = (
-                        cx.mouse.cursorx * cx.style.dpi_factor as f32,
-                        cx.mouse.cursory * cx.style.dpi_factor as f32,
-                    );
+                        self.drag_active = true;
+                        self.start_scale_factor = cx.user_scale_factor;
+                        self.start_physical_coordinates = (
+                            cx.mouse.cursorx * cx.style.dpi_factor as f32,
+                            cx.mouse.cursory * cx.style.dpi_factor as f32,
+                        );
+
+                        event.consume();
+                    } else {
+                        // TODO: The click should be forwarded to the element behind the triangle
+                    }
                 }
                 WindowEvent::MouseUp(MouseButton::Left) => {
                     if self.drag_active {
@@ -58,7 +69,12 @@ impl View for ResizeHandle {
                     }
                 }
                 WindowEvent::MouseMove(x, y) => {
-                    // TODO: Filter the hover color and dragging to the actual triangle
+                    if !intersects_triangle(cx.cache.get_bounds(cx.current), (x, y)) {
+                        cx.current.set_hover(cx, false);
+                    } else {
+                        cx.current.set_hover(cx, true);
+                    }
+
                     if self.drag_active {
                         // We need to convert our measurements into physical pixels relative to the
                         // initial drag to be able to keep a consistent ratio. This 'relative to the
@@ -188,3 +204,25 @@ impl View for ResizeHandle {
         canvas.fill_path(&mut path, paint);
     }
 }
+
+/// Test whether a point intersects with the triangle of this resize handle.
+fn intersects_triangle(bounds: BoundingBox, (x, y): (f32, f32)) -> bool {
+    // We could also compute Barycentric coordinates, but this is simple and I like not having to
+    // think. Just check if (going clockwise), the point is on the right of each of all of the
+    // triangle's edges. We can compute this using the determinant of the 2x2 matrix formed by two
+    // column ve vectors, aka the perp dot product, aka the wedge product.
+    // NOTE: Since this element is positioned in the bottom right corner we would technically only
+    //       have to calculate this for `v1`, checking the other two vectors is redundant but for
+    //       now we'll do it anyways
+    let (p1x, p1y) = bounds.bottom_left();
+    let (p2x, p2y) = bounds.top_right();
+    let (p3x, p3y) = bounds.bottom_right();
+
+    let (v1x, v1y) = (p2x - p1x, p2y - p1y);
+    let (v2x, v2y) = (p3x - p2x, p3y - p2y);
+    let (v3x, v3y) = (p1x - p3x, p1y - p3y);
+
+    ((x - p1x) * v1y) - ((y - p1y) * v1x) <= 0.0
+        && ((x - p2x) * v2y) - ((y - p2y) * v2x) <= 0.0
+        && ((x - p3x) * v3y) - ((y - p3y) * v3x) <= 0.0
+}