Skip to content

Mouse Input

Handle mouse input using the Input framework property (IInputContext).

Quick Start

protected override void OnUpdate(GameTime gameTime)
{
    // Position (Vector2 in screen coordinates)
    var mousePos = Input.MousePosition;

    // Click detection
    if (Input.IsMouseButtonPressed(MouseButton.Left))
    {
        SpawnAt(mousePos);
    }

    // Scroll wheel (float — positive = up)
    if (Input.ScrollWheelDelta != 0)
    {
        _zoom += Input.ScrollWheelDelta * 0.1f;
    }
}

Mouse Position

// Absolute position in screen coordinates
var pos = Input.MousePosition;  // Vector2
Logger.LogDebug(""Mouse at {X}, {Y}"", pos.X, pos.Y);

// Movement delta since last frame (for camera/look control)
var delta = Input.MouseDelta;  // Vector2
_cameraAngle += delta.X * _sensitivity;

Mouse Buttons

// Button held down
if (Input.IsMouseButtonDown(MouseButton.Left))
{
    DrawBrush(Input.MousePosition);
}

// Button just clicked this frame
if (Input.IsMouseButtonPressed(MouseButton.Left))
{
    SelectUnit(Input.MousePosition);
}

// Button just released
if (Input.IsMouseButtonReleased(MouseButton.Left))
{
    DropItem();
}

Available buttons: Left, Right, Middle, X1, X2

Scroll Wheel

var scroll = Input.ScrollWheelDelta;  // float
if (scroll > 0) ZoomIn();
if (scroll < 0) ZoomOut();

Common Patterns

Click Detection with Bounds

if (Input.IsMouseButtonPressed(MouseButton.Left))
{
    var pos = Input.MousePosition;
    if (pos.X >= _buttonX && pos.X <= _buttonX + _buttonWidth &&
        pos.Y >= _buttonY && pos.Y <= _buttonY + _buttonHeight)
    {
        OnButtonClicked();
    }
}

Drag and Drop

if (Input.IsMouseButtonPressed(MouseButton.Left))
{
    _dragStart = Input.MousePosition;
    _isDragging = true;
}

if (_isDragging)
{
    var current = Input.MousePosition;
    _dragOffset = current - _dragStart;
}

if (Input.IsMouseButtonReleased(MouseButton.Left))
{
    _isDragging = false;
}

Camera Pan with Middle Mouse

if (Input.IsMouseButtonDown(MouseButton.Middle))
{
    var delta = Input.MouseDelta;
    _cameraPosition -= delta;
}

Zoom with Scroll Wheel

var scroll = Input.ScrollWheelDelta;
if (scroll != 0)
{
    _zoom = Math.Clamp(_zoom + scroll * 0.1f, 0.5f, 3.0f);
}

Troubleshooting

Mouse position seems wrong

  • MousePosition returns screen coordinates (top-left origin)
  • If using a camera, convert with camera.ScreenToWorld(pos)

Scroll wheel not working

  • ScrollWheelDelta is a float, not a Vector2
  • Check in OnUpdate, not OnRender
  • Value resets each frame — check != 0, don't accumulate

Mouse delta always zero

  • MouseDelta reports frame-to-frame movement
  • Verify the mouse is actually moving over the window

Summary

Property/Method Returns Usage
MousePosition Vector2 Absolute screen position
MouseDelta Vector2 Frame-to-frame movement
ScrollWheelDelta float Scroll amount (positive = up)
IsMouseButtonDown() bool Button held
IsMouseButtonPressed() bool Button just clicked
IsMouseButtonReleased() bool Button just released

Next Steps