Canvas type (UDT)

The drawing surface a custom control paints onto. Passed to ICustomControl.Paint on every redraw pass and used exclusively from inside that method — its lifetime is the duration of the single paint pass.

A custom control builds up one or more ElementDescriptor records describing the rectangles it wants to draw — each carrying a position, size, fill, borders, corners, text, cursor, tab-index, and a set of AddressOf-registered input callbacks — and hands each descriptor to RuntimeUICCCanvasAddElement. The framework rasterises the descriptor, routes hit-testing to the registered callbacks, and (where the descriptor opts in) tracks keyboard tab order and focus.

Private Sub OnPaint(ByVal Canvas As CustomControls.Canvas) _
        Implements CustomControls.ICustomControl.Paint

    Dim descriptor As ElementDescriptor
    With descriptor
        .Left = 0
        .Top = 0
        .Width = Canvas.RuntimeUICCGetWidth()
        .Height = Canvas.RuntimeUICCGetHeight()
        Set .BackgroundFill = Me.NormalState.BackgroundFill
        .Text = Me.Caption
        Set .TextRenderingOptions = Me.NormalState.TextRendering
        .OnClick = AddressOf BtnClick
        Canvas.RuntimeUICCCanvasAddElement(descriptor)
    End With
End Sub

Methods

RuntimeUICCCanvasAddElement

Adds an ElementDescriptor to the canvas. Each element becomes one painted rectangle plus its input-handling region. Descriptors are rendered in the order they are added, so later elements paint on top of earlier ones.

Syntax: Canvas.RuntimeUICCCanvasAddElement ElementDescriptor

ElementDescriptor

required A ByRef reference to the populated ElementDescriptor UDT. The framework copies the values it needs out of the record; the caller can reuse the variable for the next element.

RuntimeUICCGetDpi

Returns the DPI of the monitor the control is currently displayed on, as an integer (the standard 96 / 120 / 144 / … values).

Syntax: Canvas.RuntimeUICCGetDpi ( ) As Long

RuntimeUICCGetDpiScaleFactor

Returns the DPI scale factor — RuntimeUICCGetDpi / 96 — as a Double. Multiply PixelCount-typed measurements by this value to convert from design-time pixels to device pixels at paint time.

Syntax: Canvas.RuntimeUICCGetDpiScaleFactor ( ) As Double

RuntimeUICCGetHeight

Returns the height of the canvas in device pixels.

Syntax: Canvas.RuntimeUICCGetHeight ( ) As Long

RuntimeUICCGetWidth

Returns the width of the canvas in device pixels.

Syntax: Canvas.RuntimeUICCGetWidth ( ) As Long