Add drag threshold to improve click experience

CHANGELOG.md

@@ -4,6 +4,7 @@
 
 - Fixed issue with CairoMakie rendering scene backgrounds at the wrong position [#4425](https://github.com/MakieOrg/Makie.jl/pull/4425)
 - Fix incorrect inverse transformation in `position_on_plot` for lines, causing incorrect tooltip placement in DataInspector [#4402](https://github.com/MakieOrg/Makie.jl/pull/4402)
+- Added threshold before a drag starts which improves false negative rates for clicks. `Button` can now trigger on click and not mouse-down which is the canonical behavior in other GUI systems [#4336](https://github.com/MakieOrg/Makie.jl/pull/4336).
 
 ## [0.21.12] - 2024-09-28
 

src/makielayout/blocks/button.jl

@@ -65,6 +65,10 @@ function initialize_block!(b::Button)
 
     onmouseleftdown(mouseevents) do _
         mousestate[] = :active
+        return Consume(true)
+    end
+
+    onmouseleftclick(mouseevents) do _
         b.clicks[] = b.clicks[] + 1
         return Consume(true)
     end

src/makielayout/mousestatemachine.jl

@@ -199,6 +199,8 @@ function _addmouseevents!(scene, is_mouse_over_relevant_area, priority)
     mouse_downed_inside = Ref(false)
     mouse_downed_button = Ref{Optional{Mouse.Button}}(nothing)
     drag_ongoing = Ref(false)
+    mouse_downed_at = Ref(Point2d(0, 0)) # store the position of mouse down so drags only start after some threshold
+    drag_threshold = 2.0 # mouse needs to move this distance before a drag starts, otherwise it's easy to drag instead of click on trackpads
     mouse_was_inside = Ref(false)
     prev_t = Ref(0.0)
     t_last_click = Ref(0.0)
@@ -231,7 +233,7 @@ function _addmouseevents!(scene, is_mouse_over_relevant_area, priority)
             else
                 # mouse was downed inside but no drag is ongoing
                 # that means a drag started
-                if mouse_downed_inside[]
+                if mouse_downed_inside[] && norm(mouse_downed_at[] - px) >= drag_threshold
                     drag_ongoing[] = true
                     event = to_drag_start_event(mouse_downed_button[])
                     x = setindex!(mouseevent,
@@ -294,6 +296,7 @@ function _addmouseevents!(scene, is_mouse_over_relevant_area, priority)
                 mouse_downed_button[] = button
 
                 if mouse_was_inside[]
+                    mouse_downed_at[] = px
                     event = to_down_event(mouse_downed_button[])
                     x = setindex!(mouseevent,
                         MouseEvent(event, t, data, px, prev_t[], prev_data[], prev_px[])