Alex Fr provided an excellent set of drawing tools in his DrawTools article and these tools serve as a basis for this article, which expands on the original toolset in the following ways:
In this article, I will describe how Layers were implemented, as well as the Text and Image tools.
See the original DrawTools article for details on how the basic application is built, class structure, etc.
It is also assumed that the reader has a working understanding of GDI+ fundamentals, including Matrices. For an excellent introduction to GDI+, see www.bobpowell.net.
Adding Layers to the application involved adding two classes, Layer and Layers, where Layer defines a single Layer and Layers defines the collection of Layers in an ArrayList.
Each Layer exposes the following properties:
private string _name;
private bool _isDirty;
private bool _visible; private bool _active; private GraphicsList _graphicsList;
Note that the Layer contains the GraphicsList - this is the key to the whole thing - each Layer contains its own list of drawing objects instead of DrawArea. DrawArea is modified to declare a Layers collection instead of a GraphicsList collection:
// Define the Layers collection
private Layers _layers;
When DrawArea is initialized, the Layers are initialized by creating the first Layer and setting it Active and Visible:
public DrawArea()
{
// create list of Layers, with one default active visible layer
_layers = new Layers();
_layers.CreateNewLayer("Default"); _panning = false; _panX = 0; _panY = 0; // This call is required by the Windows.Forms Form Designer. InitializeComponent(); }
In the Layers class, the CreateNewLayer() method actually creates the new Layer:
/// <summary>
/// Create a new layer at the head of the layers list and set it /// to Active and Visible. /// </summary> /// <param name="theName">The name to assign to the new layer</param> public void CreateNewLayer(