/// <summary>
/// Renders the visual content of the <see cref="ImageListBoxItem"/>.</summary>
/// <param name="context">
/// The <see cref="DrawingContext"/> for the rendering.</param>
/// <remarks><para>
/// <b>OnRender</b> calls the base class implementation of <see cref="UIElement.OnRender"/>,
/// and then attempts to display the current <see cref="ContentControl.Content"/> of the
/// <see cref="ImageListBoxItem"/>, depending on its type:
/// </para><list type="bullet"><item>
/// If the element is an <see cref="EntityImage"/>, its first image frame is drawn above a
/// text label showing its identifier.
/// </item><item>
/// If the element is an <see cref="ImageFrame"/>, the frame is drawn without a label.
/// </item><item>
/// If the element is a <see cref="RectI"/>, the corresponding region of the <see
/// cref="ImageListBox.FrameBitmap"/> is drawn without a label.
/// </item></list><para>
/// If the element is of any other type, or if an error occurs, the "invalid" icon returned
/// by <see cref="Images.Invalid"/> is drawn instead.</para></remarks>
protected override void OnRender(DrawingContext context)
{
base.OnRender(context);
// default to base class if not in an ImageListBox
ImageListBox listBox = Parent as ImageListBox;
if (listBox == null)
{
return;
}
// get drawing parameters of containing ImageListBox
WriteableBitmap bitmap = listBox.FrameBitmap;
ImageScaling scalingX = listBox.ScalingX, scalingY = listBox.ScalingY;
// source within bitmap and target within context
RectI source = RectI.Empty;
Rect target = new Rect(0, 0, ActualWidth, ActualHeight);
/*
* The default Background brush of a ListBoxItem is transparent, meaning that an item
* will not register clicks on anything but the non-transparent image and text label.
*
* This is very inconvenient, so we always draw a fully opaque background. We use the
* ListBox.Background brush for regular items, and the system-defined HighlightBrush
* for selected items. The Foreground brush changes automatically as appropriate.
*
* NOTE: The HighlightBrush must be drawn explicitly anyway, or else the Foreground
* of a selected item would be invisible against the Background of the ListBox!
*/
Brush background = (listBox.SelectedItem == this ?
SystemColors.HighlightBrush : listBox.Background);
context.DrawRectangle(background, null, target);
// check which content we're drawing
if (Content is RectI)
{
source = (RectI)Content;
}
else
{
ImageFrame frame = Content as ImageFrame;
if (frame == null)
{
EntityImage image = Content as EntityImage;
if (image == null)
{
goto failure;
}
// get first image frame and scaling
frame = image.Frames[0];
scalingX = image.ScalingX;
scalingY = image.ScalingY;
// compute bounds of image label
Point textLocation = new Point(0, ActualHeight - this._labelHeight);
Size textSize = new Size(ActualWidth, this._labelHeight);
// reduce image bounds accordingly
target.Height -= textSize.Height;
// draw text for image label
FormattedText text = FormatLabel(image.Id, textSize);
context.DrawText(text, textLocation);
}
// final sanity check for valid image frame
if (frame == null || frame.Source.Value == null)
{
goto failure;
}
// draw image frame with associated bitmap
bitmap = frame.Source.Value.Bitmap;
source = frame.Bounds;
}
// draw specified rectangle with desired bitmap & scaling
if (ImageUtility.DrawOutlineFrame(context, Foreground, target, bitmap, source,
listBox.Polygon, scalingX, scalingY, ColorVector.Empty, PointI.Empty, PointI.Empty))
{
return;
}
failure:
// draw "invalid" icon on failure
ImageUtility.DrawInvalidIcon(context, Foreground, target, listBox.Polygon);
}