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IFW Lightwave Textures Tutorial Four - Controlling Alpha Maps |
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| Introduction | |
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In order to show some of the aspects of Alpha Maps and how they can be used to control
on object's surface we are going to make a chrome whiffle ball. A whiffle ball
is a small light plastic ball with round holes cut in it.
Download the whiffle ball scene (11K)
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| Part 1 - A Basic Ball |
| In the modeller add a ball. Using the numeric requester make the sides and segments both 32. Ensure that the center is 0m,0m,0m for XYZ and radii is 10cm, 10cm, 10cm for XYZ. Make the sphere an in the Change Surface panel make the surface name ball and check the double-sided and smooth check boxes. Finally, save the object as WhiffleBall.lwo. |
| Part 2 - A Basic Texture |
In layout add the WhiffleBall.lwo object, bring up the surface panel and ensure
the current surface is ball. Initially lets create a basic chrome surface so
set the Color to 120,130,150 for red, green and blue. Then set the Luminosity
to 40%, the Diffuse to 0%, the specularity to 150%, the Glossiness to 16 and
the Reflectivity to 75%. Check the Color Highlights check box and set the
Reflect Options to Raytrace and Backdrop. To give the chrome something to reflect
go to the Effects Panel and check the Gradient Backdrop check box. Now, add
IFW_Dimples, set the size to .03, 0.03, 0.03 for XYZ and the Bump to 0.0. To
get the right spot layout right it is usually best to do a color test so uncheck
the Do Blending check box and set the blends to B1=17% and B2=B3=B4=100%. By turning
off the blending we have forced the texture not to interpolate the colors (and ultimately
the alpha map) so that we have a sharp transition. The figure below shows what the ball
should now look like.
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| Part 3 - Making the Holes |
In order to make the whiffle ball holes we need to make the spots which are currently
yellow transparent. To do this we are going to use an alpha map. The is basically
the same as the color map except it has single values rather then colors. These values
will be interpolated against the texture function in the same way as the color map. This
can then be used to control all surface parameters using the controls in the Affect section.
The first thing to do is enable the Transparency so in the Affect section check the check
box next to the transparency. Now to make the holes transparent we want to make the alpha
map full on (transparent) where the color is yellow and turned off (opaque) where
the color is blue. So make A1=0% and A2=A3=A4=100%. Notice how the alphas line up
to the colors. Also turn off the application of color by unchecking all four color
affect check boxes. The figure below shows what the ball should now look like.
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| Part 4 - Completing The Ball |
As you can see the texture is not quite there yet as the holes are still reflective
and have a specular highlight. What we want to do is use the alpha map to switch
these off in the holes. The problem is we only have one alpha map. However, this
can be overcome by making the alpha map control these paramters but switch them
off where appropriate. This can be done by enabling both the Reflectivty and
Specularity on the Affect section but making their values both 0%. This has the
same affect as inverting the alpha map. The figure below shows just what the completed
ball should be like. Once this is complete the scene can be modified as shown in the
overall tutorial picture at the top of the page. Here IFW_Bozo2 was used to rough-up
the chrome a bit to create diffused reflections.
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