Thursday, May 04, 2006

Shadows Passes in XSI

Alright I promised One Blog a week, but a friend needed help and I decided that beause there are not many resources to show people how to make shadow passes I would just make a blog for him to look at and then if anyone else has the same issue they can look at this as an example.
Also for those of you who like to do shadow passes by overiding primary and secondary rays, I personally find that to be more time consuming, so I have chosen to make shadow passes using Simple Shadow and Shadow Illumination properties in the render tree applyed to an overide on the surface for the objects material. I find it easier and at work have writen a script with presets so now I only press a buttom to make shadows.
I am making the assuption that who ever read this knows how to use XSI and therefore has an idea of how to make passes, partitions and create primitive objest :)
My example is just a scene with two primitives. It does not matter what you use. Just know that you need three partitions.
  1. Partition 1 contains Simple shadow objects (these are the objects that will cast shadow)
  2. Partition 2 contains Shadow objects (these are the objects that recieve Shadow)
  3. Partition 3 contains lights emiting shadow rays.

Lets start......

My scene contains two objects.

Cone will be the Simple Shadow (Shadow caster)

Grid will be Shadow (Shadow Reciever).

Simple Shadow contains Cone

Shadow contains Grid

Background Lights contains my light


Add an overridre to the Simple Shadow partition.


Add a material-suface parameter to the overide by selecting a surface node inside the shader.

Open the render tree by pressing 7.

Inside the render tree add a simple shadow node.


Connect the node to the override Material-surface imput.


Now for the shadow partition you are going to repeat the first few steps.

*Add an overridre to the Shadow partition.

*Add a material-suface parameter to the overide by selecting a surface node inside the shader.

*Open the render tree by pressing 7.
Inside the render tree add a Shadow node and a constant node.



Connect the Shadow node to the color imput for Constant and the constanct to the override Material-surface imput.

Things to note... I added a constant inbetween the shadow and the materia overdide to give light a stop point for the shadow rays.


I am adding an overide to the light, because I ussually have many lights in the scene and the lights affect the enviroment. It is easier to override a light than to hide it in every pass. So I can use a light as part as my rig and also as my shadow light for my shadow pass.

For the light partition in my shadow pass I add an intensity and shadow parameter.

When the dialog box comes up just say you want to add them as parameters.

Add your intencity value and check shadows.

That will tell XSI to turn the shawdow rays in the light on.
Things to be concern about before rendering Antialiasing and Optimisation.

Antialiasing changes on how close the objec is or if your production has presets to fallow. I did a test a moment ago and in you loca computer a min of 1 an max of 3 will be fine for a shadow pass.

For Optimization it is recommeded by the great render gods to Use a diagnostis mode and depth to determine the proper BSP settings nevertheless I have found that a min of 20 and a max of 60. Will work.

Also make sure that you have enable ray tracing on in order for shadows to render.

For reflaction and refletion for a regular shadow presets are fine.

Now render........

Change your region settings to show alpha and you should be able to see shadows.

Now if you show alpha and rgb on shaded mode. this is what you will get.

Have fun and I how this was helpful.

If you have any question email me or leave me a coment.

Monday, May 01, 2006

Artist Date !!

Alright, I know what you are thinking, but let me assure you that is not what you think.

My first day of college, my professor of figure drawing (Michael Jacques) assigned as homework to go on an artist date. What he meant was to designate, out of our busy schedule, atleast an hour to celebrate the beauty of creation. This is a broad idea, that can be interpreted in anyway posible, but for those of us who are busy it is a nice way to slow down and smell the roses if you will. Go to a museum, work in your shop, plant in your garden, play the guitar, be curious like a child, have the desire to learn. Draw, take pictures, read a book, sit at your porch and enjoy the breeze, do what ever you want to do. It is your hour, slow down and have some time with yourself.

It is about idea of exploring.

"Creativity is allowing yourself to make mistakes. Art is knowing

which ones to keep." Scott Adams

Here are some example of my artist dates.


Always carry a sketchbook. Leonardo once wrote. "You truly don't understand anything until you have drawn it.

Also don't be afraid to make bad drawings. These are not great. Greatness takes years of practice.


Taking pictures is both fun and relaxing. If you own a Digital camera. It is always easy to delete the pictures you don't like.

Click here Images these are pictures I took on a weekend.

Go to a Museum.

I love the Getty. I try to go there atleast once of month. My favorite piece is a dutch painting "Shipping in a Calm at Flushing with a States General Yacht Firing a Salute" by Jan van de Cappelle . I move throught the whole museum and this picture always makes me sit and stare. I love the dramatics and harsh angle of the painting, for it is like caos meeting order on a canvas.

Jan van de Cappelle Dutch, 1649 Oil on panel 27 7/16 x 36 5/16 in. 96.PB.7