BetterSpace

Building and Using Nebulae: (Modeler and Layout)

When the blackness of space is just too black, or if you simply want to add some colour to your space scenes, adding a nebula to your environment can be just the touch that is required to spice-up your renders. A nebula can also be very useful when the lighting in the scene leaves very dark areas on your ships and planets, which are difficult to tell apart from the background. The nebula will nicely highlight the edges of your objects, and lend more apparent depth to the scene.

There are five basic ways to produce a nebula effect using Lightwave.

This tutorial will describe techniques in Modeler, Layout and Photoshop, although most of the steps are easily translated into other software packages.

We'll start our nebula in Modeler.

Load up the starfield that you created in the previous lesson (or whatever starfield you plan to use this nebula with).

Now click on Layer 2 and put Layer 1 into the background so you can still see it.

Create a ball with the following settings:

creating a ball

Note that the 5.5Mm radius is designed to ensure that the ball completely encircles the starfield object, which has an approximate radius of 5Mm, as seen here.

ball created, stars in background layer

You can now go back to Layer 1 and delete the starfield object.

Cut and paste the ball object from Layer 2 to Layer 1 and save the object as MyNebula.lwo or something like that.

Time to do a bit of editing on this nebula object, as background nebulae could never be spherical... think about it.

Any way, using the selection tools at your disposal, make the following selection IN THE FRONT/BACK VIEWPORT.

-X		+X
selection made

Cut these polygons out, press z to delete the remaining polygons, then paste the selected polygons back into the same layer.

the remaining polygons

You should be left with an object that looks like the image above.

If you switch on your OpenGL preview, you will see that all the polygons point outwards from the center of what was the ball. This is no good to us, as we want to be able to see the inside of the ball.

Press f to flip all the polygons' orientation, and now all the polygons face inwards, towards the center of the ball.

polygons flipped

Now we are going to define the surface of the nebula.

Press q to apply a new surface and call the new surface Nebula.

Lightwave [6] surface requester

Make the surface colour pure black (000,000,000) and set the diffuse level to 0%, as we do not want this object to be affected by the scene lights. If you are using Lightwave 5.6 set smoothing to On, but if you are running Lightwave [6], don't worry, we'll do this later on.

Save your object again now.

We will now apply a temporary image map to the object in order to place the texture correctly.

Firstly, we need to work out what the dimensions of our image must be in order to prevent the image we eventually paint being stretched out of shape when we map it onto the object.

WARNING! BASIC MATHS INVOLVED!

If you created your object using the settings I specified earlier, (ie: a ball with a radius of 5.5Mm) and then cut out exactly the polygons I showed, then you are let off doing the sums. Your nebula has a radius of 5.5Mm and is 3.4Mm from top to bottom, so using basic Pythagorus theorum, we can work out that the inner circumference of our nebula is (5.5Mm x Pi) wide and 3.4Mm high.

Doing the sums, this works out as 17.28Mm x 3.4Mm. Accordingly, that is a picture aspect ratio of roughly 5:1, so our nebula image must be five times wider than it is high.

If you DIDN'T follow the instructions exactly for any reason, either go back and re do them, or work out the required aspect ratio for your nebula image. To do this, take the radius of your nebula and multiply it by Pi (3.14159...). This will give you the inner circumference of your nebula. Divide this number by the height of your nebula (use the measure tool under the Display menu to find this out) and the resulting number is your aspect ratio, so if you get something like 6.2 as the result of your calculation, it means that your nebula image must be 6.2 times wider than it is tall.

Okay, so using my settings, I'm going to create a temporary nebula image.

Open Photoshop, or whatever you use, and create a new image. My aspect ratio had to be 5:1 so I am going to create a temporary image sized 500 x 100 pixels.

Give your image a black background and just paint some quick stuff in white over the top of the black. Do try to leave a clear black border around the edges of the nebula if you can, but don't spend any time making this look nice, we'll be deleting this image later anyway.

Finally, write your name in big black letters over the top of the nebula image. You'll see why later on.

Here's what I came up with in about fifteen seconds:

mmm! nice!

Save this image out as some format that Lightwave can read (Photoshop .PSD is good) and quit Photoshop again.

We will be mapping the object cylindrically in order to minimise distortion in the mapping process.

Lightwave [6]	Lightwave 5.6
Quit Modeler, open Layout and load your MyNebula.lwo object. Open the Surface Editor and select the Nebula texture. Leave all the surface settings at their defaults, except for the the following: Surface Colour 000,000,000 (black) Luminosity 100% Diffuse 0% Smoothing ON (angle 89.5%)
Click the next to the colour settings in order to apply a texture map to the colour channel.	Click the next to the colour settings in order to apply a texture map to the colour channel.
Apply your temporary nebula image map as a Cylindrical projection through the Y axis, set the Width Wrap Amount to -2.0 and turn OFF Texture Antialiasing as shown below.
Next, press Automatic Sizing. You will see that the texture is assigned a size of X=5.5 Mm, Y=3.992 Mm and Z=11 Mm. These settings are based on the actual object we are working with, and the actual center of our object is not 0,0,0. Therefore, because we want the texture to be mapped according to the theoretical circle that this shape would define if it were a complete circle rather than a semi-circle, we need to double the value for X given by the Automatic Sizing.
In the Scale area, double the value given for the X-Scale (I doubled mine from 5.5 to 11 Mm). Next, click the Position tab and set the X-Position to be 0.	Click the Texture Size button and double the X value (I doubled mine from 5.5 to 11 Mm). Next, click the Texure Center button and set the X value to 0.
FInally, click the Use Texture button to confirm your texture settings, then close the Surface Editor and save your object.

We have now finished the modelling and texture settings for the nebula object.

Let's set up a quick test render to see what we've got and to check that everything is working OK.

Load up the scene that we saved at the end of the starfield lesson called 'Space_Environment_01.lws'.

This scene, if we look back, should have three of our starfield objects all parented to a Null Object called Space Scenery Parent.

Load your nebula object into the scene and parent it to the Space Scenery Parent object.

In the Object Properties window / Objects Panel, turn off all the shadowing options for the Nebula object. This is important because we don't want our nebula to cast its shadow on objects within the scene, and we definitely don't want the other objects in the scene to cast their shadows onto the nebula.

Change to the camera view by pressing 6 on the numeric keypad, and you should be able to see the edge of your nebula.

Select the nebula and rotate it around (don't ever move the nebula or starfield objects) until you get a view of the nebula that you like.

rotating the nebula into position

When you get a good view, press F9 and have a look at the render.

Let's just check that the nebula is mapped correctly. The first thing to check is that the lettering of your name is not backwards, upsidedown, squished or otherwise messed up. If it is, firstly check to make sure that you set the Width Wrap Amount in the texture options to -2.0 and not 2.0... this is the most common cause.

Next. rotate the nebula around so that you can see the left-edge of the object like this:

left edge of the nebula

Don't trust the OpenGL preview here, it often lies about mapping information when it comes to cylindrical mapping, especially in Lightwave 5.6. Do a quick render to make sure that the nebula image fits the nebula geometry properly.

If all is well, rotate the nebula so you can see the right edge and repeat the render process.

right edge of the nebula

If your nebula image does NOT fit the geometry properly, it is most likely because your nebula object is oriented in the wrong direction. Go back to Modeler and rotate the object 90 degrees around the Y axis, then bring it back to Layout and try rendering again.

When you are content that your nebula is working properly, save your scene as Space_Environment_02.lws and save all the objects in the scene too.

Now, go to frame 0 on the time slider and rotate your camera so that is looking at one edge of the nebula. Next, go to frame 200 and rotate the camera so that it is looking at the other edge of the nebula.

Set the camera resolution to 400x200 pixels, turn on motion blur and particle blur and render a quick animation to see what you've got.

In the next lesson we will paint a decent nebula image map in Photoshop, then apply this to our nebula object and look at a few tweaks we can make to the nebula at render time.

Do you have any comments of questions regarding this lesson?