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This chapter is from the book


An excellent strategy for efficient rendering is to augment scenes with scanned images or animated texture maps onto flat surfaces, known commonly as cards or billboards. This is used to optimize an otherwise unmanageable scene or simply to add more detail cheaply. As an electronic version of paper dolls, there are limitations, because the elements must remain roughly perpendicular to the camera and in the background. Cameras cannot roam around them. A good application, though, would be crowd scenes, trees, cityscapes, or otherwise overly heavy background elements. Note that you must match the lighting in your card image to the scene in which they are being placed, possibly resetting some light direction in Photoshop using the Render Lighting filter. You must also mask out the object, making sure that the area outside the object's alpha is black. Now use this map in an Incandescent channel in a Lambert shader and turn the Color channel down to black. Map a file copy of the Alpha channel to the Transparency channel, which acts as a stencil and creates the look of complex geometry with the expense of a single polygon. Animated maps can be used as well, which are useful for tree leaf rustling or pedestrians walking. This very simple trick is used much more than you might think in many well-known film effects scenes. Just goes to show that the best tricks are often the simplest!

Figure 3.3Figure 3.3

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