The Art of Art Assets - Building a Simple Bridge : Part 1a
Polygon and Triangle Counting
Polygons are simply multisided objects. When a polygon is created, the quads that are formed are bisected by triangles. The amount of triangles used in a game can add up quickly and cause performance issues. This is when polygon and triangle counting at the beginning of your project becomes a very important step in creating usable art assets. Here is an image of the included polygon counter that comes with 3D Studio Max.
While modeling, I usually have this tool open. You can select individual objects in your scene and gain an instant polygon count. As you can see from the above screenshot I have selected an object in a randomly selected scene that has a count of 226. This is a pretty good size for a simple object in a level. More complex objects such as vehicles and characters should maintain triangle sizes of around 2500 to 3500. Please note that these numbers can change depending on the type of game rendering engine used. For our project we will try and shoot for a model that has a count of around 3500 triangles. Note that in the polygon counting tool you can set the parameters of your budget. This is an outstanding way to manage sizes for a particular piece of your object and attain your overall budget goals.
Finding a Reference Photo
Google is a great source for reference images. The following image is what I will be using as a reference for the bridge tutorial.
Normally you would want to find multiple pictures to reveal different angles of your object in an attempt to piece together a more realistic model. Fortunately for the simplicity of our bridge, our chosen image will work just fine.
Analyzing the Object
The defining features of the bridge that are readily apparent consist of the lower bent H Steel bars, interconnected supports, and the upper railing. If you look closely you can see that the crisscrossed supports have holes, and therefore when they are repeated will cause a very large performance hit for our model. Another performance consideration is the repeating box shape railing, each of which contains multiple faces. Before you begin this project it might be a good idea to draw out a diagram of your bridge in pieces before you start modeling.
I quickly created a sample of one of the supports we will be using in an attempt to emphasize modeling constraints outlined in the Analyzing Key Architectural Elements paragraph. Although the polygon count of this object seems low (around 68) the amount of triangles used is HUGE. This is because I used a Boolean Subtract of an 8 sided cylinder 5 times in a rectangular box shape. Although the strut looks like it would fit great in our bridge, we will run into performance problems later. Keep in mind our bridge object will require 40+ of these support bars.
Look at all those triangles in the above image! To form the shape of those ngon holes you’ll notice that the support became quickly complex and the triangles required are enormous. The triangle count in the above object is unacceptable for our efforts.
We will address the solutions to these types of problems encountered in the modeling process as we progress further into the tutorial.
Building the Pieces
Building the H-Bar Supports with Splines
Open up 3D Studio Max if you haven’t already and do a quick save, name it bridge.max or something equally original. Under the spline edit tool select the ‘Line’ tool. Create an H shape in the left orthographic view. Notice that each time you click in the view you are laying down vertices.
Make sure that you end up with a closed spline. A closed spline is accomplished by ending the placement of your vertices at the first vertices you created.
You might need to align the vertices of your shape if it looks disproportionate. In order to edit the vertices of your spline it must be converted to an ‘Editable Spline’. To convert your shape you can right click it, and then from the context menu select Convert To: > Convert to Editable Spline.
Give your shape a name such as “HBar_Left”. Naming objects in your scene is always good practice. With your editable spline selected you can now go into vertex selection mode and move the vertices until you’re satisfied.
For the next step we are going to apply a bevel modifier to our spline to cap the shape and extrude it to specified distance. With the spline selected, select ‘Bevel’ from the modifier drop down list.
You will now be presented with some options that allow you to change the parameters associated with the bevel modifier. Go ahead and set the Capping to Start and End if it isn’t already. The Surface should have Linear Sides. Also make sure you have 6 segments. Each of the segments represents the position of a support strut. Under the ‘Bevel Values’ menu heading, set the Height of our H Bar to 1000.0.
Align and center your H Bar with the grid in the front and left viewports, this will become important when we re-orient the pivot-point. Your H Bar should look like the following.
Increase the number of segments and take a look at the polygon count, notice how more segments increases the faces of your object. Bring the segment number back to 6. A quick triangle count shows a nice round number of 164. We will only be using 2 of these H Bars in our model which adds up to a nice round 328 triangles.
In this next step we will be moving the pivot point to the center of the H Bar. With our object selected click the ‘Hierarchy’ tab. Make sure the ‘Pivot’ button is selected. Under Adjust Pivot and in the Move/Rotate/Scale: group, select Affect Pivot Only. This will put you in a mode that allows you to move the pivot of your object. Go ahead and select the pivot from the front view and put it in the center of the object. Make sure that the pivot is also aligned in the left view as well.
Deselect the ‘Adjust Pivot’ button and click the modifier tab. With the H Bar still selected you should be back in an editable mode.
The next step will be to add a Bend modifier to our H Bar modifier stack. In the modifier list select ‘Bend’. In the parameters for your bend modifier set the Angle and Direction to 90. Your H Bar should now be bent downward. If the bend is not where you expected it to be, select the Center submenu from the Bend modifier and move the
axis to the objects center. The axis is visible as a yellow cross (as seen above). You should now have a completed H Bar support weighing in at 164 triangles.
Total Triangle Count: 164
Now that we have a nice H Bar we are ready to move on to building the crisscross supports
Click here to proceed to Part 1b