Polygon Objects
Polygon objects represent one or more filled polygons that share a given set of vertices and rendering attributes. All polygons must be simple (the edges of the polygon should not intersect) and convex (the shape of the polygon should not have any indentations). Concave polygons can be converted into convex polygons using the helper object IDLgrTessellator. See Tessellator Objects for more on tessellator objects.
Creating Polygon Objects
To create a polygon object, provide a two- or three-dimensional array (or two or three vectors) containing the locations of the polygon's vertices to the IDLgrPolygon::Init method. For example, the following statement creates a square with sides one unit in length, with the lower left corner at the origin:
Setting vertex data upon initialization is the same as using the DATA property. You can also use the POLYGONS property to define the object shape as described in Creating Polygon and Polyline Objects.
See "IDLgrPolygon" (IDL Reference Guide) for complete reference information.
Configuring Polygon Objects
Polygon objects have numerous properties controlling how they are rendered. You can set these properties when creating the polygon object, or use the SetProperty method to the polygon object to change these properties after creation.
Style
Set the STYLE property to an integer value that controls how the polygon is rendered. Set the STYLE property equal to 0 (zero) to render only the vertices. The following statement changes the polygon to display only the vertex points, in blue:
Set the STYLE property equal to 1 (one) to render the vertices and lines connecting them. The following statement draws the polygon's outline in green:
The default setting for the STYLE property is 2, which produces a filled polygon. The following statement draws the filled polygon in red:
Vertex Colors
You can supply a vector of vertex colors via the VERT_COLORS property. The colors in the vector will be applied to each vertex in turn. If there are more vertices than colors supplied for the VERT_COLORS property, IDL will cycle through the colors. For example, the following statements color each vertex and connecting line one of four colors:
vcolors =[[0,100,200],[200,150,200],[150,200,250],[250,0,100]] mypolygon->SetProperty, STYLE=1, VERT_COLORS=vcolors
Fill Patterns
As demonstrated in Pattern Objects, you can fill a polygon with a pattern contained in an IDLgrPattern object. Set the FILL_PATTERN property equal to the object reference of the pattern object. If you have created a pattern object called mypattern, the following statement uses that pattern as the polygon's fill pattern:
Shading
IDL provides two types of shading for filled objects. In Flat shading, the color of the first vertex in each polygon is used to define the color for the entire polygon. The polygon color has a constant intensity. In Gouraud shading, the colors along each line are interpolated between vertex colors, and then along scanlines from each of the edge intensities.
Set the SHADING property of the polygon object equal to 0 (zero) to use flat shading (this is the default), or equal to 1 (one) to use Gouraud shading. In the above example using vertex colors, adding the following statement:
creates a polygon fill in which the color values are interpolated between the vertex colors.
Texture Mapping
You can map an image onto a polygon object by specifying an IDLgrImage object to the TEXTURE_MAP property. The TEXTURE_COORD property defines how individual data points within the image data are mapped to the polygon's vertices. Note that you must specify both TEXTURE_MAP and TEXTURE_COORD to enable texture mapping.
