AS9 Getting Started: A Step-by-step Tutorial
Let's walk through the steps you take starting from your
scene in SLIDE and ending with a photo-realistic rendering (using
Pixie or BMRT). I'm going to assume everyone has installed either Pixie
or BMRT and successfully rendered at least one sample RIB file. If
that's not the case, you want to do that before proceeding further.
I'm going to use a simple scene with three squares - one texture mapped
floor and two side walls. There is an area light on the top. This is the SLIDE file I start with. It uses
this texture file (a simple wood texture). Note
this file contains a texture map and light specification - the things
you need to use for this project. So, this file is a good
representative example. Also note that the cyan-like color on the walls
is an effect of the cyan ambient light color.
Here are the steps you will take to go from the SLIDE representation to
a rendered image.
Now you're set to play around with both the renderers. This is a good
time to make sure you have a very good, almost final scene in SLIDE.
Then, you can devote your time to making it look good on Pixie or BMRT.
- Produce a RIB file.
This should be straightforward. If SLIDE crashes with this simple file,
there is something wrong with your SLIDE installation (esp. on Win32).
Try re-installing SLIDE. This is the RIB
file I get after saving the scene as RIB from SLIDE.
- Convert the texture file to a
You should first make a ".tif" file from the texture image file - any
program like GIMP, PhotoShop, MS Image Viewer will do (remember to save
as a 24 bit image). Then, you should convert the TIFF file to a ".tx"
format (for those who care - this does mipmapping). This isn't
absolutely necessary (i.e. both BMRT and Pixie will accept raw TIFF
files as well), but will give you better texture quality and
On BMRT, you use the 'mkmip' command. On Pixie, use 'texmake'.
- View your RIB files using the
Using BMRT, you should be able to invoke the renderer on the RIB file
generated by SLIDE, without modifying it. Use the 'rendrib' command.
You should get something like this:
For Pixie, you'll notice that simply running Pixieto render the RIB
file produced in step1 will only render the light and nothing else.
This is because Pixie does not support area light sources. You should
manually modify the light type to something Pixie can support (like a
point light, say). This is the RIB
file that works with Pixie. After rendering this file with Pixie
(with the 'rndr' command), you get something like this:
- Add Surface Shaders
If you inspect the RIB files, you'll see several 'Surface' commands
with names like 'plastic', 'paintedplastic', 'constant' etc. in them.
You are already using shaders! The names that follow the 'Surface'
commands (i.e. plastic etc.) are the names of the shaders and
everything that follows the shader name are name-value attribute pairs.
That is, if you see something like "Ka"  , it means we're passing 1
as the value of the ambient component to the shader. If you don't have
any arguments after the shader name, the shader will use default
values. To see the default values of a shader, open the corresponding
shader file (these are the *.sl files in the 'examples' directory for
BMRT and 'shaders' for Pixie).
Obviously the scene above needs improvement. You can experiment with
different shaders to find one that matches your requirements. Also,
once you identify the shader, you should understand the parameters it
takes so you can play around with those values as well.
Now, for no particular reason, let's make one of the side walls out of
shiny metal. Also, since more of you have had trouble with Pixie, we'll
modify the Pixie RIB file. This is the modified RIB file. Notice the
'Surface "metal"' command just before the geometry for the left wall is
specified. Also note that the surface attribute needs to be enclosed
with corresponding "AttributeBegin" and "AttributeEnd" tags. After
rendering this with Pixie, this is what you should get:
Ok, so granted this looks even uglier than the earlier image, but the
point is we were able to modify the shader without much work. Now, the
hard part is figuring out the exact lighting conditions and correct
parameters for a shader so this looks good. That's up to you!
Again, for no good reason, I decided I want the left wall to be made
out of glass instead. So, I use the glass shader; this is the modified RIB file.
After rendering it using BMRT, this is what you should get:
Notice the reflection of the light and floor on the left wall.
- Add visibility information to
the shaders (for Pixie)
This is where you take into account inter-object occlusion
You will need to do this for Pixie; you modify two things:
(1) RIB file (add the Attribute "visibility" tags)
(2)Shader file (the
After this, you will also have gained some very useful insight into modifying
Of course, the scene above doesn't really need any shadow generation,
but if you're using Pixie, you should do this step - without soft
shadows, your scene will never look photorealistic, and you'll lose
- Add Lights to your scene
You should play around (in SLIDE) with different types of
lights - last week we discussed how for an outdoors shot, you would
need directional light and for an indoors shot, you'll need a spot or
- Further Improvements
Play around with anti-aliasing (sampling more than once per pixel),
radiosity etc. These things take time to render, so do this step last.