IDL is the abbreviation for Image Description Language. Each instance of the IDL class contains data that describe an image using a set of opcodes which must be interpreted and used to render the image. The opcodes are interpreted and based in a virtual rendering context that supports a set of state attributes and a set of instructions (opcodes). The instructions either modify the state attributes of the rendering context or they cause drawing operations to be performed, using the current rendering context state.

You can find more detailed information about the opcodes and the state attributes in the IDL properties and the static hashtable opcodes.

The coordinate system

A point in the IDL is infinitely small and a line or a Bezier curve are therefore infinitely thin as well. An IDL point with the coordinates 0,0 is projected onto the center of the screen pixel with the coordinates 0,0. This projection model differs from that used in SVG and the Canvas implementation, but it fits in with the model used by VML. We settled on this model simply because it makes rendering easier to understand and to handle.

The following example creates a 2D image, 64 x 64 pixels, showing a semi-transparent red rectangle, centered within the image and with a 1 pixel black opaque border:

 // Create a new IDL object.
var IDL = nokia.maps.gfx.IDL,
		parseCss = nokia.maps.gfx.Color.parseCss,
		top = IDL.opcodes,
		attr = IDL.attributeToIdentifier,
		idlImage = new IDL(
 [
		// Create a new image with a size of 64x64 pixel
		op.BEGIN_2D_IMAGE, 64, 64, "MyImage",

		// Create a new path that follows a rectangular shape with the top-left 
		// corner of the bounding box at 16, 16 and a width and height of 32 x 32 
		// pixels
		op.BEGIN_PATH,
		op.MOVE_TO, 16, 16,
		op.LINE_TO, 47, 16,
		op.LINE_TO, 47, 47,
		op.LINE_TO, 16, 47,
		op.CLOSE_PATH,

		// Fill and stroke the path
		op.SET, attr.fillColor, parseCss("red", 0.5),
		op.SET, attr.strokeColor, parseCss("black",1.0),
		op.SET, attr.lineWidth, 1.0,
		op.FILL,
		op.STROKE
 ]);

 // Create an instance of the best painter for the current browser and  
 // platform and paint the IDL image into the document body
 var body = document.body || document.documentElement,
     DefaultPainter = nokia.maps.gfx.Painter.defaultPainter,
     painter = new DefaultPainter();
 body.appendChild(painter.createElement(idlImage, document));

Note that we do not recommend that you create an IDL object directly; it is better to use the class nokia.maps.gfx.Graphics for this purpose. The reason is that although "hand optimized" opcode can be small and maybe efficient in certain implementations, for exaple, a Canvas painter, but it can cause suboptimal performance if used with other painters such as VML, while the graphics context generates code that runs well in all implementations.