Two Dimensional Views (Pure 2D)

Two Dimensional Mode of KernelCAD components allow displaying items which are two dimensional by its nature, namely sets of lines, points and 2D shapes.

Two Dimensional view (2D View) keeps internally a 2D item set, which is a 2D analogue of 3D model. Although 2D set is often generated from 3D model of the component it can be completely independent.

Use IView2.SetViewType to switch between two and three dimensional modes of the component. 2D View functionality is controlled via I2DView_KC Interface, which cal be obtained via: KernelCAD > GetView > IView > I2DView_KC

2D Views have number of properties (see the table below), which define how the items are displayed. Programmatically these properties can be managed via IKCContext queried from the I2DView_KC.

2D Views have also a 3D frame associated with it. The frame is called Frame of 2D View. It is used for mapping between 2D coordinates of the view and 3D coordinates of the main model.  x and y plane of the frame is called plane of the view. The frame, hence position and orientation of the plane can be set arbitrary via IFrame and other related frame interfaces queried from the IKCContext.

There are two ways to add 2D items to the 2D item set:

1. 2D Mapping

With this method 2D items are generated by mapping 3D objects of the main model of the component to 2D coordinate axes and adding the results to the 2D scene automatically. Currently there are two methods of mapping:  intersection and projection.

2D mapping is very useful for displaying planar sections of objects or projections to a plane It requires minimal programming.

Both methods use frame of the view (see above) to define the plane on which the image is generated and orientation of 2D axes inside the plane. 2D x and y axes are x and y axes of the frame of view.

With intersection mapping each object of the 3D model is intersected with plane of the view (see above). If intersection is not empty intersection line is mapped to local x and y coordinates of the frame of view and added to 2D scene as a new item.

With projection mapping each object of the 3D model is projected to the plane of the view. The result will look as if the 3D point of view has changed so that the viewer is looking along negative direction of z axis of the frame of view and y axis is up.

The projection  works on per patch basis. A 3D patch is projected as a polygon (curvilinear in general case) rendered as line loop of its edge. When hidden line removal is enabled (default) lines which are covered by a higher polygon (the 3D edge from which the line was projected is invisible in 3D from end of z axis of the frame of view) are removed. Projected lines are mapped to local x and y coordinates of the frame of view and added to 2D scene as a new item.

The above work is performed during UpdateSurface call. when view type is set to 2D.

2D items keep information about its z position along z axis of the frame of view.

To use 2D Mapping mode:

1. Set view type to 2D with IView2.SetViewType(EViewType.eViewType2D)
2. Query I2DView_KC via: KernelCAD > GetView > IView > I2DView_KC
3. Obtain IKCContext via I2DView_KC.GetContext.
4. Set required mapping type with IKCContext.SetIntParam(0, E2DViewGeometryType.e2DViewGeometryTypeIntersection ) or IKCContext.SetIntParam(0, E2DViewGeometryType.e2DViewGeometryTypeProjection )
5. Use IFrame or/and IFrame2 queried from the IKCContext. to set position and orientation of the plane of the view and x, y axes inside the plane.
6. Call UpdateSurface to create the 2D items and display them in the view

See Cross View Sample for an example.

2. Direct Definition

With Direct Definition method 2D items are defined and added to the scene directly without any reference to any 3D objects.

To use Direct Definition mode:

1. Set view type to 2D with IView2.SetViewType(EViewType.eViewType2D)
2. Query IKCContext via: KernelCAD > GetView > IView > I2DView_KC > IKCContext
3. Query IDraw from IKCContext.
4. Use IDraw.Begin, IDraw.Vertex, IDraw.End to add lines, points or shapes to the 2D item set. Use I2DView_KC.AddText to add text stings at specified locations
5. Use I2DView_KC.AddText to add text strings
6. Call UpdateView to redraw the window

Note that IDraw is used here in an unusual way. Instead of normal drawing of a single scene it is used to define geometry, which will be used in multiple rendering with possible window resizing, etc.

See MidImplementation.AddProjection() method of Cross View Sample for an example.