Controlling Surface Transparency in Hull Modeling

[Terrance Egolf]

This issue probably isn’t a burning one for users primarily interested in designing and assembling full-sized vessels, where hydrostatic characteristics and overall appearance are the main features of interest. However, many users at my urging have been introduced to the utility of Delftship for modeling purposes. For those, such as myself, who wish to create digital ship models leading to plans for bookshelf models or using the program to validate existing 2D plans, the appearance of the resulting 3D model is as important as the 2D plans created from the program.

One of the great detractions from images showing shaded surfaces exported from the program is the existence of crease edges that would under normal circumstances be hidden by opaque surfaces between the object and the viewer. Rather than simply being a general transparency of the whole object, these lines only appear if within a certain distance of the front faces of the intervening objects. For complex models with lots of detailed objects, this visibility can be intrusive. Here is an image of my model of a 19th century sailing ship with “Show shaded surface edges” selected in the Settings|Preferences|Hullform tab.

Note the spaghetti of additional lines that surround the various structural objects. The rail balusters are small enough that they appear transparent—you can see the crease edges all the way around them.

If the user deselects the  “Show shaded surface edges” setting, then the objects in the image can only be discerned by differences in color and shading. These greatly rely on viewing orientation and the direction of the default light source. Because of the shader characteristics of the program, this leads to loss of detail and even ambiguity regarding the shapes of modeled objects:

The ability to see below the modeled surface when trying to manipulate control points and observe the edges of surfaces is really beneficial while modeling. However, for trying to display finished products as illustrations, or perhaps for a client, the extraneous crease edges can be intrusive.

I suggest that the program provide the ability to eliminate the partial surface transparency that now occurs and permit solid surfaces to be truly opaque, showing only those shaded crease edges that can be visible from a given viewpoint. This improves the definition of objects from any viewpoint and eliminates the washed-out appearance of images with shaded surface edges turned off.

A related problem occurs when viewing surfaces with lots of edges that are in front of other geometry. With shaded surfaces turned on you can still see the vague outlines of those objects where the crease edges occur in the foreground object, as if there are tiny gaps between the edges and their connected surfaces.

Please let me know if there is any other information or examples I can provide to clarify this problem.

Terry

• This topic was modified 1 year, 6 months ago by Terrance Egolf.
• This topic was modified 1 year, 6 months ago by Terrance Egolf.

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[Maarten]

Hi Terry,

Thank you for the kind words. Sadly this is something we have investigated in the past and have not been able to solve. It has to do with how OpenGL draws faces and edges- in order to keep the edges visible (at all) the need to have some preference over the faces. Without this setting the output results would become unpredictable, making either edges or faces ‘disappear’ from view.

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