Event Types Reference: Click, Drag, Key, Focus, and Scroll

Prowl.Paper dispatches strongly typed event objects to element callbacks. Every callback receives a concrete event class whose fields describe what happened — mouse position, key pressed, drag delta, and so on. All pointer-based events derive from ElementEvent, which provides common spatial data. This page documents every event type, the callback that delivers it, and every public field on each class.

Inheritance overview

ElementEvent                    ← base class for all pointer events
  ├── ClickEvent                ← OnClick, OnPress, OnHeld, OnRelease, OnDoubleClick, OnRightClick
  ├── DragEvent                 ← OnDragStart, OnDragging, OnDragEnd
  └── ScrollEvent               ← OnScroll

FocusEvent                      ← OnFocusChange  (standalone, not pointer-based)
KeyEvent                        ← OnKeyPressed   (standalone)
TextInputEvent                  ← OnTextInput    (standalone)

`ElementEvent` — base class

ElementEvent is the base for all pointer-driven events. It provides position data in three coordinate spaces and a propagation-control mechanism. Namespace: Prowl.PaperUI.Events

Properties

Source

ElementHandle

The element that originally triggered the event. When an event bubbles to a parent, Source is retargeted to the new element via the internal Retarget() method, so it always reflects the current element handling the event.

ElementRect

Rect

The calculated layout rectangle of the source element in screen coordinates.

PointerPosition

Float2

The raw pointer (mouse cursor) position in screen coordinates at the moment the event fired.

RelativePosition

Float2

The pointer position relative to the element’s top-left corner. (0, 0) is the top-left corner of the element.

NormalizedPosition

Float2

The pointer position mapped to a [0, 1] range within the element. (0, 0) is the top-left corner; (1, 1) is the bottom-right corner.

IsPropagationStopped

bool

Indicates whether event bubbling has been halted for this event. Read-only; set it via StopPropagation().

Method

public void StopPropagation()

Prevents the event from bubbling further up the element tree. Only affects the current event instance — other event types on the same element are unaffected. Equivalent to DOM’s Event.stopPropagation().

element.OnClick(e =>
{
    HandleClick(e);
    e.StopPropagation(); // parent elements will not see this click
});

`ClickEvent`

Fired for all mouse-button click interactions. The specific interaction is identified by the Phase property. Namespace: Prowl.PaperUI.Events
Base: ElementEvent

Callbacks that receive `ClickEvent`

Callback	Phase value
`OnClick`	`ClickPhase.Click`
`OnPress`	`ClickPhase.Press`
`OnRelease`	`ClickPhase.Release`
`OnHeld`	`ClickPhase.Held`
`OnDoubleClick`	`ClickPhase.DoubleClick`
`OnRightClick`	`ClickPhase.RightClick`

Properties

Button

PaperMouseBtn

The mouse button that triggered this event. See PaperMouseBtn below.

Phase

ClickPhase

Identifies the click phase:

ClickPhase.Click — standard single click (press + release)
ClickPhase.Press — button just pressed down
ClickPhase.Release — button just released
ClickPhase.Held — button held beyond the hold threshold
ClickPhase.DoubleClick — two clicks within the double-click time window
ClickPhase.RightClick — right mouse button click

All ElementEvent properties (PointerPosition, RelativePosition, NormalizedPosition, ElementRect, Source) are also available.

Example

button
    .OnClick(e =>
    {
        Console.WriteLine($"Clicked at {e.RelativePosition} with {e.Button}");
    })
    .OnPress(e =>
    {
        // Finger is down — start visual press state
        isPressed = true;
    })
    .OnRelease(e =>
    {
        isPressed = false;
    })
    .OnDoubleClick(e =>
    {
        OpenDetail();
        e.StopPropagation();
    });

`DragEvent`

Fired during mouse drag operations. Provides both per-frame delta movement and the total displacement from the drag origin. Namespace: Prowl.PaperUI.Events
Base: ElementEvent

Callbacks that receive `DragEvent`

Callback	Phase value
`OnDragStart`	`DragPhase.Start`
`OnDragging`	`DragPhase.Dragging`
`OnDragEnd`	`DragPhase.End`

Properties

StartPosition

Float2

The screen-space pointer position where the drag began. Constant for the entire drag gesture.

Delta

Float2

The pointer movement since the previous frame. Use this for incremental updates such as moving a window or scrubbing a value.

TotalDelta

Float2

The total pointer displacement from StartPosition to the current frame. Use this when you need the cumulative offset rather than the per-frame change.

Phase

DragPhase

Identifies the drag phase:

DragPhase.Start — drag gesture began this frame
DragPhase.Dragging — drag is ongoing (fires every frame while dragging)
DragPhase.End — drag gesture ended this frame (mouse button released)

Example

float panelX = 0f;
float panelY = 0f;

titleBar
    .OnDragStart(e => { /* optional: save initial position */ })
    .OnDragging(e =>
    {
        panelX += e.Delta.X;
        panelY += e.Delta.Y;
    });

`ElementEvent` as `OnHover` / `OnEnter` / `OnLeave`

The hover callbacks receive the ElementEvent base class directly (no subclass):

Callback	Fires when…
`OnHover`	Pointer is currently over the element (fires every frame)
`OnEnter`	Pointer just moved onto the element this frame
`OnLeave`	Pointer just moved off the element this frame

All standard ElementEvent fields are available: PointerPosition, RelativePosition, NormalizedPosition, ElementRect, Source.

element
    .OnEnter(e =>
    {
        isHovered = true;
    })
    .OnLeave(e =>
    {
        isHovered = false;
    })
    .OnHover(e =>
    {
        // e.NormalizedPosition.X → 0.0 at left edge, 1.0 at right edge
        highlightX = e.NormalizedPosition.X;
    });

`FocusEvent`

Fired when an element gains or loses keyboard focus. Namespace: Prowl.PaperUI.Events
Base: none (standalone class)

Callback

OnFocusChange

Properties

Source

ElementHandle

The element whose focus state changed.

IsFocused

bool

true if the element just gained focus; false if it just lost focus.

Example

textField.OnFocusChange(e =>
{
    isFocused = e.IsFocused;
    if (!e.IsFocused)
        ValidateInput();
});

`KeyEvent`

Fired when a keyboard key is pressed while an element holds focus. Respects the auto-repeat settings configured on the Paper instance. Namespace: Prowl.PaperUI.Events
Base: none (standalone class)

Callback

OnKeyPressed

Properties

Source

ElementHandle

The focused element that received the key event.

Key

PaperKey

The key that was pressed. See the complete PaperKey enum listing below.

IsRepeat

bool

true when this event was generated by the auto-repeat mechanism (key held past the repeat delay), rather than a fresh key-down. Use this to distinguish “user just pressed Enter” from “Enter is being held”.

Example

textField.OnKeyPressed(e =>
{
    if (e.Key == PaperKey.Enter && !e.IsRepeat)
        SubmitForm();

    if (e.Key == PaperKey.Escape)
        CancelEdit();

    if (e.Key == PaperKey.V && paper.IsKeyDown(PaperKey.LeftControl))
        PasteFromClipboard();
});

`ScrollEvent`

Fired when the mouse wheel is scrolled over an element. Namespace: Prowl.PaperUI.Events
Base: ElementEvent

Callback

OnScroll

Properties

Delta

float

The scroll wheel delta for this frame. Positive values typically indicate scrolling up/forward; negative values indicate scrolling down/backward (exact sign depends on the host platform’s input delivery).

All ElementEvent properties are also available.

Example

scrollContainer.OnScroll(e =>
{
    scrollOffset -= e.Delta * scrollSpeed;
    scrollOffset = Math.Clamp(scrollOffset, 0f, maxScroll);
});

`TextInputEvent`

Fired once per printable character entered while an element has keyboard focus. Handles encoding-aware character input, including IME composition results. Namespace: Prowl.PaperUI.Events
Base: none (standalone class)

Callback

OnTextInput

Properties

Source

ElementHandle

The focused element receiving text input.

Character

char

The printable character entered. Carriage returns (\r) are automatically normalized to newlines (\n) by the input pipeline before this event fires.

Example

textField.OnTextInput(e =>
{
    if (e.Character == '\n')
        ConfirmInput();
    else if (!char.IsControl(e.Character))
        buffer += e.Character;
});

OnTextInput is designed for building text editors and input fields. For hotkey detection, use OnKeyPressed with PaperKey instead — TextInputEvent only fires for characters that map to printable glyphs.

`PaperKey` enum

PaperKey enumerates all keyboard keys recognized by Prowl.Paper’s input system. Pass values to KeyEvent.Key comparisons, paper.IsKeyDown(), paper.IsKeyPressed(), and related query methods. Namespace: Prowl.PaperUI

public enum PaperKey
{
    Unknown = 0,

    // Alphanumeric keys
    A, B, C, D, E, F, G, H, I, J, K, L, M,
    N, O, P, Q, R, S, T, U, V, W, X, Y, Z,

    Num1, Num2, Num3, Num4, Num5, Num6, Num7, Num8, Num9, Num0,

    // Function keys
    F1, F2, F3, F4, F5, F6, F7, F8, F9, F10, F11, F12,

    // Special keys
    Enter, Escape, Backspace, Tab, Space,
    Minus, Equals, LeftBracket, RightBracket, Backslash,
    Semicolon, Apostrophe, Grave, Comma, Period, Slash,

    CapsLock, PrintScreen, ScrollLock, Pause,
    Insert, Home, PageUp, Delete, End, PageDown,
    Right, Left, Down, Up,

    // Keypad
    NumLock, KeypadDivide, KeypadMultiply, KeypadMinus, KeypadPlus, KeypadEnter, KeypadEquals,
    Keypad1, Keypad2, Keypad3, Keypad4, Keypad5, Keypad6, Keypad7, Keypad8, Keypad9, Keypad0,
    KeypadDecimal,

    // Modifier keys
    LeftControl, LeftShift, LeftAlt, LeftSuper,
    RightControl, RightShift, RightAlt, RightSuper,

    // Media keys
    AudioNext, AudioPrevious, AudioStop, AudioPlay, AudioMute,

    // Application control keys
    Application, Menu, Select, Help
}

Modifier key helpers

Modifier keys are queried directly on the Paper instance rather than through KeyEvent, because they may be pressed when no OnKeyPressed callback fires:

bool ctrl  = paper.IsKeyDown(PaperKey.LeftControl) || paper.IsKeyDown(PaperKey.RightControl);
bool shift = paper.IsKeyDown(PaperKey.LeftShift)   || paper.IsKeyDown(PaperKey.RightShift);
bool alt   = paper.IsKeyDown(PaperKey.LeftAlt)     || paper.IsKeyDown(PaperKey.RightAlt);

`PaperMouseBtn` enum

PaperMouseBtn identifies mouse buttons in ClickEvent.Button and Paper pointer query methods. Namespace: Prowl.PaperUI

Value	Description
`Unknown`	Unrecognized or unset button (default / sentinel value)
`Left`	Primary (left) mouse button
`Middle`	Middle mouse button / scroll wheel click
`Right`	Secondary (right) mouse button
`Button4`	Extra button 4 (commonly “back” on gaming mice)
`Button5`	Extra button 5 (commonly “forward”)
`Button6`	Extra button 6
`Button7`	Extra button 7
`Button8`	Extra button 8

element.OnClick(e =>
{
    switch (e.Button)
    {
        case PaperMouseBtn.Left:   HandlePrimary(); break;
        case PaperMouseBtn.Right:  ShowContextMenu(e.PointerPosition); break;
        case PaperMouseBtn.Middle: OpenInNewTab(); break;
    }
});

Event quick-reference

ClickEvent

Callbacks: OnClick, OnPress, OnRelease, OnHeld, OnDoubleClick, OnRightClick
Key fields: Button, Phase, PointerPosition, RelativePosition

DragEvent

Callbacks: OnDragStart, OnDragging, OnDragEnd
Key fields: Delta, TotalDelta, StartPosition, Phase

ElementEvent

Callbacks: OnHover, OnEnter, OnLeave
Key fields: PointerPosition, RelativePosition, NormalizedPosition

ScrollEvent

Callbacks: OnScroll
Key fields: Delta, PointerPosition, NormalizedPosition

FocusEvent

Callbacks: OnFocusChange
Key fields: IsFocused, Source

KeyEvent

Callbacks: OnKeyPressed
Key fields: Key (PaperKey), IsRepeat, Source

TextInputEvent

Callbacks: OnTextInput
Key fields: Character, Source

Paper Class

Element Builder

Types & Enums

Documentation Index

​Inheritance overview

​ElementEvent — base class

​Properties

​Method

​ClickEvent

​Callbacks that receive ClickEvent

​Properties

​Example

​DragEvent

​Callbacks that receive DragEvent

​Properties

​Example

​ElementEvent as OnHover / OnEnter / OnLeave

​FocusEvent

​Callback

​Properties

​Example

​KeyEvent

​Callback

​Properties

​Example

​ScrollEvent

​Callback

​Properties

​Example

​TextInputEvent

​Callback

​Properties

​Example

​PaperKey enum

​Modifier key helpers

​PaperMouseBtn enum

​Event quick-reference

ClickEvent

DragEvent

ElementEvent

ScrollEvent

FocusEvent

KeyEvent

TextInputEvent

Build docs developers (and LLMs) love

Inheritance overview

`ElementEvent` — base class

Properties

Method

`ClickEvent`

Callbacks that receive `ClickEvent`

Properties

Example

`DragEvent`

Callbacks that receive `DragEvent`

Properties

Example

`ElementEvent` as `OnHover` / `OnEnter` / `OnLeave`

`FocusEvent`

Callback

Properties

Example

`KeyEvent`

Callback

Properties

Example

`ScrollEvent`

Callback

Properties

Example

`TextInputEvent`

Callback

Properties

Example

`PaperKey` enum

Modifier key helpers

`PaperMouseBtn` enum

Event quick-reference