Mouse API makes it way too hard to track button pressed

[tig]

To illustrate what I think is wrong with the current Terminal.Gui (and v1) API in this regard, consider this class.

    public class MouseDemo : View
    {
        public MouseDemo ()
        {
            CanFocus = true;
            MouseEvent += (s, e) =>
                          {
                              if (e.MouseEvent.Flags.HasFlag (MouseFlags.Button1Pressed))
                              {
                                  ColorScheme = Colors.ColorSchemes ["Toplevel"];
                              }
                              if (e.MouseEvent.Flags.HasFlag (MouseFlags.Button1Released))
                              {
                                  ColorScheme = Colors.ColorSchemes ["Dialog"];
                              }
                          };
            MouseLeave += (s, e) => { ColorScheme = Colors.ColorSchemes ["Dialog"]; };
        }
    }

I want this view to show the "TopLevel" colorscheme while button1 is pressed; when button1 is released, or the mouse leaves the view, the color should go back to "Dialog".

Here's how it behaves now. Note that if I press button1 outside of the view and drag into the view, the color changes to "Toplevel". This is not what I want. The current API provides me no way of knowing that the Button1Pressed flag was set while the mouse was outsdie of my view.

Now, I can work around this like this, but this is awful.

    public class MouseDemo : View
    {
        private bool _button1PressedOnEnter = false;
        public MouseDemo ()
        {
            CanFocus = true;
            MouseEvent += (s, e) =>
                          {
                              if (e.MouseEvent.Flags.HasFlag (MouseFlags.Button1Pressed))
                              {
                                  if (!_button1PressedOnEnter)
                                  {
                                      ColorScheme = Colors.ColorSchemes ["Toplevel"];
                                  }
                              }
                              if (e.MouseEvent.Flags.HasFlag (MouseFlags.Button1Released))
                              {
                                  ColorScheme = Colors.ColorSchemes ["Dialog"];
                                  _button1PressedOnEnter = false;
                              }
                          };
            MouseLeave += (s, e) =>
                          {
                              ColorScheme = Colors.ColorSchemes ["Dialog"];
                              _button1PressedOnEnter = false;
                          };
            MouseEnter += (s, e) =>
                          {
                              _button1PressedOnEnter = e.MouseEvent.Flags.HasFlag (MouseFlags.Button1Pressed);
                          };
        }
    }

FWIW, the impact of this behavior can be seen (in v1 and v2) in theWindows & FrameViews scenario.

Press button1 while in the Bounds of 1 - Windows Loop... and drag up.

I think there should be a View.MouseButton1Pressed and View.MouseButton1Released event.

Originally posted by @tig in #3290 (comment)

[BDisp]

How about only using the MouseEnter and MouseLeave events and dealing with the buttons that are pressed when they are invoked?

[tig]

That's what the code above does. I think having to do that is cumbersome.

[BDisp]

I think there should be a View.MouseButton1Pressed and View.MouseButton1Released event.

I recommend to create 3 events as MouseDown, MouseUp and MouseMove, passing the sender and the MouseEventEventArgs which can handle any button. The MouseMove can have button pressed or not, since there are report mouse position.

[dodexahedron]

That's what the code above does. I think having to do that is cumbersome.

Agreed it's cumbersome and even a little odd for that function.

One thing though: For any new or modified code: Please use actual named private methods (not lambdas) when subscribing to public events in library code. Additionally, making those methods static will both perform better (both CPU and heap memory impact) and force or encourage better and more testable code for the event and whatever code caused it to be raised.

And remember that any single instance of any delegate can target 0 to n methods, so don't assume that your subscriber is the only one, the first one, nor that it will even get called at all or exactly once, if part of a public event.

For code that doesn't do those things when I get to events, it will be done at that time, so don't worry about it for existing code if you don't feel like it (though it will make those diffs easier to grok when they come). But please do for new work. 🙏

[BDisp]

Here's how it behaves now. Note that if I press button1 outside of the view and drag into the view, the color changes to "Toplevel". This is not what I want. The current API provides me no way of knowing that the Button1Pressed flag was set while the mouse was outsdie of my view.

@tig you want when press button 1 in the view changes color to Toplevel and when drag outside with the button pressed, changes the color to Dialog and when drag again into the view with the button still pressed, change the color to Toplevel. Right?

[tig]

I don't think asking the question that way makes sense.

As a View, i want to know when the user has pressed a button down.

Then I want to know the user has kept the button pressed (regardless of whether the mouse was moved or not).

The current api only gives me the later.

[BDisp]

I don't think asking the question that way makes sense.

As a View, i want to know when the user has pressed a button down.

Imagine the button was pressed on a view and the MouseGrabView is set to that view with WantContinousButtonPressed as true.

Then I want to know the user has kept the button pressed (regardless of whether the mouse was moved or not).

The task ProcessContinuousButtonPressedAsync or the ButtonPressed+ReportMousePosition will continue raise the MouseEvent. Then we check if the View poroperty is the same as MouseGrabView.

The current api only gives me the later.

With WantContinousButtonPressed as true you will always have mouse events raised.

[tig]

I don't think you're getting what I'm puttin' down.

This has nothing to do with MouseGrabView or WantContinuous.

Today if a user presses the mouse button, moves it a bit, and then releases it, Applicaiton.OnMouseEvent is called with:

MouseButton1Pressed 
MouseButton1Pressed | ReportMousePosition
MouseButton1Pressed | ReportMousePosition
...
MouseButton1Released
MouesButton1Clicked

What I want is:

MouseButton1Pressed 
MouseButton1Down | ReportMousePosition
MouseButton1Down | ReportMousePosition
...
MouseButton1Released
MouseButton1Clicked

[BDisp]

I'm my opinion it isn't the mouse API that have to track those behavior but the View itself. The MouseButton1Pressed or the MouseButton1Down is the same.
When I open the Buttons scenario it still is having the MouseButton1Pressed | ReportMousePosition. I'll try to find why, but I suspect that have to do with Windows Terminal.

[tig]

I'm my opinion it isn't the mouse API that have to track those behavior but the View itself. The MouseButton1Pressed or the MouseButton1Down is the same.

I'd like to undertstand WHY you think this.

I disagree because:

The ideal way to design a UI library API is to have the API match how end-users think. End users, using mice, think in terms of

• I press the mouse button down to start an operation
• I move the mouse with the mouse button already pressed
• I release the mouse button
• I may continue moving the mouse after releasing the button

The current Terminal.Gui API does not follow this at all. It provides no event for the first action.

Other mouse APIs do. For example Windows provides WM_LBUTTONDOWN which is only sent when the mouse button first goes down.

WindowsForms: MouseDown is only fired when the mouse is first pressed.

I propose the View API looks like this.

// Passes all Application mouse events on; lets views have total flexiblity
protected internal virtual bool OnMouseEvent (MouseEvent mouseEvent); 
 // When the user first presses the button down over a view
protected internal virtual bool OnMouseDown (MouseEvent mouseEvent);
// When the user moves the mouse over a view, or if mouse was grabbed by the view. Flags will indicate if a button is down.
protected internal virtual bool OnMouseMove (MouseEvent mouseEvent);
// When the user lets go of the mouse button. Only received i the mouse is over the view or it was grabbed by the view.
protected internal virtual bool OnMouseUp (MouseEvent mouseEvent);
// When the user presses down and then releases the mouse over a view (they could move off in between). 
// If they press and release multiple times in quick succession this event will be called for each up action
protected internal virtual bool OnMouseClick (MouseEvent mouseEvent);
// When the user presses and releases the mouse button twice in quick succession without moving the mouse outside the view
protected internal virtual bool OnMouseDoubleClick (MouseEvent mouseEvent);
// When the user presses and releases the mouse button thrice in quick succession without moving the mouse outside the view
protected internal virtual bool OnMouseTripleClick (MouseEvent mouseEvent);

The logic for determining which of these methods to call could either be in Application.OnMouseEvent or in View.NewMouseEvent.