Define Initial View

Purpose

The Define Initial View function indicates to the DWF reading application what portion of the logical coordinate space should initially be viewed.

Syntax

X1,Y1 The logical coordinates of the lower-left corner of the area to be viewed

X2,Y2 The logical coordinates of the upper-right corner of the area to be viewed

Name A quoted view name as defined by Define Named View.

Details

The Define Initial View opcode tells the DWF reading application what area of the drawing's logical coordinate space should initially be viewed. This can be used when you want the user's initial view of a drawing to be a small subset of the entire logical coordinate drawing area.

This opcode can also be used when a DWF drawing does not fully fill the logical coordinate space. Although the DWF reading application may compute the extent of all graphic primitives in the scene and automatically set the view to tightly fit the scene, this requires that the entire scene be transmitted and parsed before rendering may begin with the correct view. Indicating an initial view near the start of the .dwf file allows a DWF reading application to render the scene while it is being transmitted and parsed.

Note that the view may be specified either as two logical points, or as a quoted ASCII view name as found in the active named view list.

Notes

DWF reading applications may receive multiple conflicting view instructions, and therefore should select a view based on the following precedence:

1. If this .dwf file was loaded by the execution of a URL, and the URL indicated a view, use it,
2. else if the .dwf file contains a view opcode, execute it,
3. else if the .dwf file contained a Define Drawing Bounds opcode, use the drawing extents as the view,
4. else if the entire .dwf file has been transmitted and parsed, compute the extents of all geometric primitives in the scene and use that as the view,
5. else set the view to the entire logical coordinate space.

DWF reading applications may receive view information from the execution of URLs. The specification of this behavior is to be determined (TBD).

It is possible that a .dwf file will have multiple view opcodes which can be used to animate the drawing while the file is being parsed. However, only the first view opcode, normally found in the Define Drawing Information Block block, is the official "initial" view.

Default

By default the initial view is the full 31-bit logical coordinate space.

Implementation in WHIP! Versions

 See Also

Set Projection, Define Drawing Information Block, and Define Drawing Bounds