delta3d

The Art of Art Assets - Building a Simple Bridge : Part 1b

Building the Crisscross Supports

You should be somewhat familiar with using splines for this next part. We need to create a simple shape for our framed crisscross supports. Start by creating a frame for our support.



The outline was created using the spline line tool. The inside rectangle was created using the spline rectangle tool. The rectangle was aligned to the support outline using the Align tool. With the support outline selected you need to click the Attach button and then select the rectangle to create a single spline object. Make sure that the two shapes are aligned properly before you attach.

The shape of our object still needs some work. We will be using our spline tools to refine our shape and add the support struts. This is where some of your past experience with spline editing is required. I will try and talk you through the process but it is assumed youíre already familiar with basic vertex, segment, and spline manipulation.

For the following I was in Vertex mode and using the Refine button Iíve added a few points where our supports will be located. I evenly spaced the refined points out so that the shape of our struts will be uniform. Youíll also note that in the below picture I have removed the spline segments and vertex between the new points. This is due to the fact that we want to create one shape. Youíll also notice the refined vertex points that are on the support outline, I used these extra points to align the inside vertex points correctly. The extra vertex points will need to be removed.

The next part of our spline editing will be to Connect our lines to the appropriate diagonal vertices. In Vertex mode click the Connect button, select a vertex in the left view and while holding the left mouse button drag the mouse to the correct vertex. You will create lines that look like the following.

Alright we are almost finished with our shape. The only thing we have left is to break the points in the middle and then connect our shape to form triangular holes. In Segment mode press the Break button and then, where the vertices in the middle cross, break the segments. You should have 4 of the segments broken.

Now here comes a tricky part. We need to remove segments in the middle and still maintain the vertices. I suggest you first delete 1 segment, go into vertex mode, and then connect the corner vertex with the appropriate one in the center. Repeat this process until your shape looks like the following.

All the vertices at this point should be connected.

I would like to point out something you may be wondering. Why didnít we just do a Boolean union between 2 box shapes and our beveled outline? In most cases you want to stay away from Boolean operations for game art. I maintain this view from the fact that in most cases the triangulation and hidden faces created from this operation can sometimes cause more trouble than the benefits gained. In some cases Boolean operations can be useful, however for our efforts it is not.

Next we need to add a bevel modifier to our object. Make the Level 1 Height of the bevel modifier 4.0. In the surface properties there should only be 1 segment. The support frame should look like the following.


Total Triangle Count: 108

If you notice that your object has any strange dimples or areas that look slightly concave or convex, make sure that the vertices are set to ĎCornerí and not ĎBezier Cornerí. You can change the type by right clicking directly on a vertex and selecting the appropriate menu item from the context sensitive menu. The final object surface should be flat.

Make sure you notice any problems with your object now, because in a few more steps we will be cloning it 16 times.

Building the railing

The railing is very straight forward.

First create a rectangular spline 500 units in width and 30 units in length.

Next create a smaller rectangle that has a length of 20 units and a width of 8 units. Align the smaller rectangle center to center with the larger rectangle.

For this next step we are going to use the Array tool. With the smaller rectangle selected, select the menu item Tools>Array from the main menu bar. This will open up a dialog that allows you to create copies of an object at predefined distances from each other. Make sure you are creating references of the rectangles.

First we will create to the left.

And then to the right.

The next step is very straight forward. You need to attach all the rectangles together. Select the large rectangle and press the Attach Mult. Button. This will give you a list of objects that you can attach to this one. Press the All button and then press the Attach button.

Add a bevel modifier to the finished shape with a width of about 2.0. You should have something that looks like the following.


Total Triangle Count: 512

Youíve probably noticed the hit we just took on our total triangles. This is because of all the faces weíve just added to our object. A way we could have gotten around this is with textures where a transparent alpha between the railings would have created the same effect. The detail of that process is beyond the scope of this tutorial but I wanted you to be aware of your options.

Building the Road

The road is extremely simple. Just create a box shape that is 500 units long with a height of 1 unit and a width of 50 units.


Total Triangle Count: 12

Building the Pieces Conclusion

Now that we have all the pieces for our bridge letís do a polygon and triangle count to make sure we are on target. Remember that our total budget is 3500 triangles.

Quantities Triangles Totals
H Bar Supports 2 164 128
Crisscross supports 17 108 1836
Railing 2 512 1024
Road 1 12 12
Total - - 3000

Depending on your situation you can add more detail to make the geometry of your objects more interesting. You could create small segments to break up the road, maybe add a shaped top to the railing, or you could add some support joists in interesting areas of the crisscrossed supports. Although there is room for a little more detail, for the purpose of this tutorial our objects thus far are complete. This concludes the construction of the individual pieces of our bridge.

The next section deals with assembly. Click here to proceed.

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delta3d is a game and simulation engine appropriate for a wide variety of simulation and entertainment applications. delta3d uses best-of-breed open source technologies to create a fully integrated game engine and with content creation tools.MORE

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