I made a quick tutorial on “how to render a model reflecting a world image on a white background” since it took me a pretty long time to figure it out. With this little tutorial I want to achieve a result simular to this render (click) of Luigi from Pixar’s Cars. As you can see the car model is reflecting a desert environment (clearly visible on the headlights and chrome parts), while this environment ain’t visible in the background. Instead, the background is totally white (well, it’s actually a gradient) like it is an infinite floor. Note that the car is casting a shadow on this floor though!
Now, how do we make such a render? The method I use is quite easy though there might be easier and/or better solutions. Feel free to post them in reply!
1. SCENE SETUP
I made a basic scene featuring Suzanne (monkey) on a simple plane (which will act as a shadow-casting object). The light setup ain’t important for this tutorial; just make sure there is at least one light source with “Ray Shadow” of “Buf. Shadow” enabled.
2. WORLD TEXTURE/ENVIRONMENT
Put up a texture (photo) in the 'World buttons" panel and make sure to but it on Hori in the “Map to” tab (1). This photograph will act as the environment and thus will be reflected in the model.
3. SETTING UP THE WHITE BACKGROUND
To make sure the world texture is not visible in the background, we set up an image that will be rendered as the background instead. To do this, we go to the “Scene” panel and load an image in the “backbuf” box (2). I used a totally white image to get a result similar to the Pixar render but of course, you can use any image you want.
4. MATERIALS SETUP
The Suzanne material has to be reflective (so that you can actually see the desert reflections) so I enabled “Ray Mirror” and increased the value of “RayMir”. (3)
The ground shouldn’t be visible but should cast shadow. Therefore we enable “ZTransp” in the “Links and Pipeline” tab to make it transparent (4) and “OnlyShad” in the “Shaders” tab to make it only cast shadows (5). Next, I decrease the alpha value (6) in the “Material” tab to make the shadows less dark and to avoid jagged edges (see note below). In this example I set alpha to 0.5.
Note: Leaving alpha to 1, resulted in some nasty jagged edges. Increasing the AA samples didn’t solve the problem, using another sampling filter helped a bit.
Make sure “Ray (tracing)” and “Shadow (calculation)” is enabled in the “Scene” panel and just hit F12! That’s it.
Another way to get this result is by rendering an RGBA-image (PNG or so) and pasting the white (or gradient) background in later with nodes or in a graphics editing program such as Photoshop of The Gimp. You don’t have to set up a white backbuf image then of course. This method provides more freedom and possibilities but is more work to set I guess.
Hope you liked this short tutorial.