Only resize when clicking on the triangle part

nih_plug_vizia/src/widgets/resize_handle.rs

@@ -39,6 +39,12 @@ impl View for ResizeHandle {
         if let Some(window_event) = event.message.downcast() {
             match *window_event {
                 WindowEvent::MouseDown(MouseButton::Left) => {
+                    // 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);
 
@@ -48,6 +54,11 @@ impl View for ResizeHandle {
                             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
+}