The Art of Art Assets - Building a Simple Bridge : Part 3

UVW Mapping

I would like to warn you up front that this section is not for the impatient. This area is a requirement to the texturing process and will take a lot of time. UVW coordinates refer to the objects XYZ coordinates in relation to the worlds center. In order to take a 3D object and pull out mapping coordinates we need to essentially 'unwrap' the UVW coordinates of our object. With an unwrapped object we can create a 2D image, texture it, and then apply it back to our 3D model. Luckily the process of applying an Unwrap UVW modifier and moving around texture coordinates of our model is very easy.


UVW Unwrap

First convert your bridge to an Editable Mesh. This can be performed by right clicking the bridge group and under the context menu item ‘Convert To’ select ‘Convert to Editable Mesh’.

We will be doing very simple texturing of this model to help get your feet wet. First off we need to assign a UVW unwrap modifier to our model. With the bridge selected add a UVW Unwrap modifier from the drop down modifier list.

From here we need to click the [+] next to the added UVW Unwrap and click on Select Face.

Click the Edit button in the unwrap rollout. You will be presented with the following window.

This is where you will be performing most of your work. The blue rectangle in the window represents our UVW coordinate space. If you were to go outside the boundaries of this space it would repeat on the other side. In the perspective view go ahead and select the entire model (I usually just hit ctrl-a). This will highlight all the faces of your model in red to show that they have been selected.

Now, back in the Edit UVWs window, and in the main menu bar, select Mapping>Normal Mapping. This will open up another dialog that asks you how you would like to go about Normal Mapping your selection.

Now because we have an object that is very boxy we will be choosing ‘box mapping’. Other than the type of Normal Mapping the rest of the properties are ok. Go ahead and click the OK button to apply your mapping. You’re Edit UVWs window will now look similar to the following.

Now you’ll notice that there are a lot of overlapping parts to our model. I’ll show you one example of how to move pieces of the model around and then you can take it from there. A step by step tutorial for the entire unwrap process would be 20 pages long so I’ll only cover the basics.

Start out by thinking how you want the texture artist to be able to paint the model. Which areas would you like painted and in how much detail. Since we will be consolidating similar shapes to the same coordinates to save space, you’ll need to decide how you want your model broken down. I have decided that I want my textures painted on the road, the sides of the model, the front, the faces of the crisscross supports and the railing. I’m not too worried about the other faces of the model. You will see how this will unfold as this section progresses.

Let’s grab the railing first and pull it out of our UVW space. In the perspective view deselect all the selected faces (just left click the mouse button off the model). Now, while holding the ctrl button, start selecting the front faces of the bridge.

With those faces selected hit the ‘Planar’ button located in the uvw modifier properties list.

This will cause the coordinates of your selection to become planar in the edit UVW’s window.

With the faces selected move the planar coordinates over to the side. You need to resize the faces to something proportional to the rest of the bridge. Use the uniform scale tool to resize.

Do this for all the faces in your model, grouping areas that you think should be together, or areas that you want painted as one piece. The unwrapping really comes down to personal preference and creativity. This is what my final unwrapping looks like.

When you are finished unwrapping your model it will need to be collapsed. Do a collapse of your model and then go to the main menu bar and select Render>Render to Texture. This will open up a bake to texture window where you can create a 2D image that your texture artist can use.

Render to Texture

Pick an output path for the image. Under mapping coordinates choose the ‘Use Existing Channel’ and make sure you have Channel 1 selected.

Add a Diffuse Color to the Target map Slot.

Give the image a name under File Name and Type. Select a size of 1024. Go ahead and hit the Render button at this point. Your coordinates will be baked and the final image will be ready for the texture artist.

I apologize for the brevity of this section, however we could spend days discussing UVW unwrapping techniques. With your final 2D image ready, head on to the next section to see a wrap up of our model (no pun intended… ok maybe a small one).

This ends part 3 of our tutorial, click here to continue to part 4.


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