Chapter 9 Modeling with Polygon Meshes

From ShadeCamp

In this chapter we’ll model a horse using a polygon mesh. We’ll create the horse’s left side and then copy this to the right half as a mirror image. This will reduce the amount of work involved and create a symmetrical object.

Contents 1 Creating the Basic Shape 2 Modeling More Features 2.1 Modeling an Ear 2.2 Modeling the Legs 3 Using Mirror Copy 4 Merging the Two Halves

Creating the Basic Shape

1. Open BT_09_horse.shd from the Documentation-Samples tab in ShadeExplorer. In this scene the outline of a horse has been drawn in the Side view.
   

First let’s select View > Mesh to display the Mesh Toolbox. The Mesh Toolbox contains the tools used exclusively for editing polygon meshes.

1. Select Extrude from the Solid tool and click and drag in the Front view to extrude the outline as shown.
   
2. Select the Extruded closed line in the Browser and then select Convert to Polygon Mesh from the Convert tool. A dialog appears asking you to specify the level of subdivision used when creating the mesh. Click OK in the dialog to confirm the default Regular subdivision. The extruded closed line is converted to a polygon mesh.
   
3. Now let’s choose Enter Modify Mode (from the Modify tool) to start editing the polygon mesh.
4. In the Mesh Toolbox select Face Selection mode. This will allow us to select the faces of the polygons. Click and drag across at least two faces in the Front view to select them.
   
   Then click the Belt tool in the Mesh Toolbox. This expands the selection to include all the polygon faces in a “belt” around the mesh.
   
5. Select the Knife tool in the Mesh Toolbox.
   
   The knife tool is used to divide a single polygon face into two faces. To do this, click and drag along the center of the polygon mesh in the Front view as shown here. All the selected polygon faces split into two halves.
   
6. Now we’ll select the the left half of the mesh as viewed from the front. Click and drag across the two front left polygons forming the horse’s head. Then click the Belt tool again to select all the polygon faces on the left side.
   
   
7. Select the Offset tool in the Mesh Toolbox.
   
   We will use the Offset tool to enlarge the polygon faces we have selected. Click at the origin in the Front view and drag upwards. A virtual joystick appears as a guideline. As you drag upwards the size of the selected faces grows, and the unselected faces stretch to accomodate them. The Y axis will be the center of the horse, so this will eventually result in a rounder animal shape.
   
8. Now we’ll change the shape of the horse’s outline to squares to make it easier to edit from the Side view. Select Vertex Selection mode in the Mesh Toolbox.
   
   While holding down Z (Win) or Option (Mac), click and drag from the control point at (1) to the control point at (2) in the figure. Release the mouse button when the cursor icon displays a point in the lower left corner as shown here. (If the cursor doesn’t display a point when you complete the operation, the new line won’t be connected to a second control point.)
   
9. Next add a line between points (3) and (4) in the figure to the right using the same technique as in Step 9.
   
10. Switch the Preview Display Mode to Shading in the Perspective view to make it easier to verify that the shape is correct. To do this, right-click in the Perspective view and select Display Mode > Shading + Wireframe from the contextual menu.
11. Open the Camera window by clicking the camera icon in the Aggregate window or by selecting View > Camera.
    
    Rotate the camera in Eye mode until you can see the opposite side of the mesh (the side that won’t show after we complete the horse’s right side).
    
12. Select the Face Selection Mode in the Mesh Toolbox and click the side of the mesh. Press Delete to remove this face from the polygon mesh. To return the camera view to the front side of the mesh, click the << button below the virtual joystick in the Camera window.
    
13. Now select the two polygon faces that form the horse’s back. Click and drag across both faces to select them at once. Use the Knife tool in the Top view to divide the polygons laterally, as shown.
    
14. Switch to Vertex Selection Mode to select the vertices of the new edge you added in Step 14. Click and drag upwards in the Side view to give the horse’s back a slight arch.

Modeling More Features

Modeling an Ear

1. Click the Face Selection Mode button in the Mesh Toolbox to switch back to face selection mode. Select the faces that form the top of the horse’s head and use the Knife tool to divide the polygons near the top of the head, as shown here.
   
2. Now we’ll make the ear. Click the top right polygon in the Front view to select it and choose the Extrude tool from the Mesh Toolbox.
   
   Click and drag downwards along the virtual joystick to extrude the polygon face outwards, and drag to the left to shrink the size of the face. If necessary you can use Translate from the Move tool to adjust the position.

Modeling the Legs

1. In the Side view select the bottom polygon face (the horse’s belly). Next use the Knife tool to divide the polygon into three sections. (The first section for the front legs, the middle section will be the belly, and the last section will be the hind legs.)
   
   If you click Continuous Mode before using the Knife tool you can make multiple Knife operations without needing to reselect the tool inbetween.
2. Hold Sift and click the polygons that will form the front and hind legs to select them all simultaneously.
   
3. Now hold Sift + Z (Win) or Sift + Option (Mac) and click and drag downwards to create the horse’s legs above the knee. This will actually copy and move the selected polygon faces.
   
   Repeat this operation three more times to create the knee, lower leg and hoof parts.
   
4. The last step in modeling the left side of the horse is to switch to Vertex Selection Mode and adjust the positions of the vertices for a more organic look. The legs look a bit stiff, so add some shape for the hooves and knees.
   

Using Mirror Copy

Now we will copy the horse’s left side over to the right using the Mirror Copy tool located in the Mesh Toolbox.

1. While in Modify Mode, select Edit > Select All. You should see all the polygons in the mesh become highlighted.
   
2. Click the Mirror Copy tool in the Mesh Toolbox. In the Front view, click on the Y axis (exactly at the edge of the polygon mesh) and drag to the left to copy a mirror image of the mesh to the left.
   
3. The horse should now look like the image on the right. If you make a mistake choose Edit > Undo and try the Mirror Copy again.
   

Merging the Two Halves

1. Open the Object Info window by clicking the “i” icon in the Aggregate window or choosing View > Object Info. Set the Roundness slider to 1 (all the way to the right).
   
2. Now let’s preview the figure by switching the Persepctive view to Shading display mode. You’ll notice that there is a small gap in the center of the horse. This is caused by the fact that the vertices we selected when doing the mirror copy operation were also copied, creating extra points in the center of the polygon mesh. To fix this, we’ll merge the points together.
   
3. Select the Vertex Selection tool in the Mesh Toolbox to switch to vertex selection mode, and in the Front view select all the points along the Y axis.
   
4. Select Align center (left/right) from the Align tool in the Mesh Toolbox. This will
   
5. Now select the Merge Points button (labeled “merge”) in the Mesh Toolbox. The horse should now appear without any gap between the left and right sides.
   
6. Render an image of the horse now, or experiment with adding more detail to the figure. For more information on working with polygon meshes see the User Guide.
   
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