public virtual void Draw(IViewport view, Graphics canvas, WebRequestsPool pool)
{
// Viewport is readonly.
Debug.Assert(view != null, "Viewport is missing!");
Debug.Assert(canvas != null, "Canvas is missing!");
Debug.Assert(pool != null, "WebRequestsPool is necessary for image downloading!");
var builder = new StringBuilder();
GetVisibleLayerNames(builder, IsCrsSupportedByParents());
if (builder.Length > 0)
{
var newView = view.Copy();
newView.ReduceViewBox(Wms.MaxWidth, Wms.MaxHeight);
var newImage = new MapImage(builder.ToString(), Wms.CRSId, newView, ImageFormat,
IsTransparent, BgColor);
try
{
// We cannot work with variable directly,
// because another thread could rewrite it during the work.
var oldImage = ReleaseImage();
try
{
if (IsVisible)
{
// Are we downloading?
if (AutoUpdate && Wms.IsDownloadingEnabled)
{
if ((oldImage == null) || (!newImage.Equals(oldImage)))
{
var requested = newImage;
newImage = null; // Do not dispose the object
pool.PutRequest(this, requested, requested.GetImageAddress(Wms));
if (oldImage != null)
{
oldImage.Draw(view, canvas);
}
}
else
{
// If the situation changes and there is requested the same image
// that already exists in the layer, outdated downloading is running
// at this moment and it must be interrupted.
pool.RemoveRequest(this);
oldImage.Draw(view, canvas);
}
}
else
{
// Downloading must be interrupted.
pool.RemoveRequest(this);
if (oldImage != null)
{
// Use an image with different CRS is nonsense.
if (oldImage.CRSEquals(newImage))
{
oldImage.Draw(view, canvas);
}
else
{
oldImage.Dispose();
oldImage = null; // Erase old image
}
}
}
}
else
{
if ((oldImage != null) && (!newImage.Equals(oldImage)))
{
oldImage.Dispose();
oldImage = null; // Erase old image
}
}
}
finally
{
// If another thread save new image, we prefer it.
SetOrErase(oldImage);
}
}
finally
{
if (newImage != null)
{
newImage.Dispose();
}
}
}
else
{
EraseImage(pool);
}
}