在Monogame中用鼠标实现拖放

Question

I'm trying to implement some windows in my test app, and now I'm trying to make these windows able to be dragged.

Check that awesome illustration to see what I'm trying to do, and what actually happens:

First, I check if the mouse position is on top of the window and if the left mouse button is pressed and held, here:

if (mouseOver && LastLeftPressed && MouseLeftPressed)
{
     onHoldClick(Events);
}

This is what I've tried:

private static void onHold(object sender, EventArgs e)
{
    var LastMouse = mousePosition;
    mousePosition = Mouse.GetState().Position;
    var window = sender as Window;
    if (LastMouse != mousePosition)
    {
        var deltaX = mousePosition.X - LastMouse.X;
        var deltaY = mousePosition.Y - LastMouse.Y;
        window.Rectangle = new Rectangle(mousePosition.X - deltaX, mousePosition.Y - deltaY, Width, Height);
    }
}

Sometimes the results are really weird, such as the window jumps to random positions, but usually the results are as the illustration above. When I click'n'hold and move the mouse really slowly, the window will be instantly moved to the mouse's position.

I can't figure this out.

Answer 1

I would have done something like that...

Class fields:

private object grabbedObject;
private Vector2 grabOffset;
private MouseState mouseState; // update each Update() call

When mouse button down:

Vector2 mousePosition = new Vector2(this.mouseState.X, this.mouseState.Y);
Vector2 objectPosition = Vector2.Zero;
this.grabbedObject = GetClickedObject(mousePosition, out objectPosition);
if (this.grabbedObject != null)
{
    this.grabOffset = new Vector2(
        mousePosition.X - objectPosition.X,
        mousePosition.Y - objectPosition.Y);
}

private object GetClickedObject(Vector2 pMousePosition, out Vector2 pObjectPosition)
{
    Object clickedObject = null;
    // search first object you clicked on and set to clickedObject  
    pObjectPosition = clickedObject == null ? Vector2.Zero : clickedObject.Position;

    return clickedObject;
}

When mouse button up:

if (this.grabbedObject != null)
{
    // process drop action

    this.grabbedObject == null;
    this.grabOffset = Vector2.Zero;
}

When drawing:

if (this.grabbedObject != null)
{
    Vector2 position = new Vector2(
        this.mouseState.X - this.grabOffset.X,
        this.mouseState.Y - this.grabOffset.Y);
    // and so on...
}

Answer 2

I found where my problem was. I was mistakenly moving the window to mousePosition.X - deltaX but instead I should have done window.Rectangle.X - deltaX .

Basically, I was offsetting the window based on the mouse's position; however, the correct way was to offset the window based on its own position.

Here is the fixed line.

window.Rectangle = new Rectangle(window.Rectangle.X + deltaX, window.Rectangle.Y + deltaY, Width, Height);