Autodesk 62205-051408-9001 User Guide - Page 384

14 Creating Particle Effects Choosing a Shape Size The size of a shape image is not limited, but here is a tip to optimize the use of texture memory on your OpenGL card. Texture memory is used in chunks whose size must be a power of 2 (16, 32, 64, 128, 256, 512, 1024, and so on). If the height or width of an image is between two of these numbers, the higher number is used for the texture memory. So if an image is 128 x 128, the memory required is 128 x 128 pixels. If the image is 129 x 128, the memory required increases to 256 x 128 pixels. As a guideline, you should use 128 x 128 particle shapes (or smaller) unless you know you need to use larger ones. When you drastically scale up small particle shapes (using the Size properties), they can appear blurred with some "jaggies." Likewise, when you drastically scale down large particle shapes, they can appear too sharp, and they may speckle. The 128 x 128 shape size is a good compromise-the particles look decent when scaled up (but not too large), and they also look decent when scaled down. Using the Shape Library Usually, shapes are in the shape library because they are used by emitters in the emitter library. Both libraries are saved in the same ELC file. When a shape is used in the emitter library, it means at least one particle type for one emitter uses it. But you can add other shapes to the shape library; a shape can be added without being immediately used. Using Library Shapes The easiest way to assign a shape to a particle type is to use an existing one. You swap the current shape with one from the current library or another library. For example, when the Templates library is loaded, the shape library shows only one shape. If you want to use a shape in another emitter library, first add the emitter from the Templates library to the viewport, then load another library that includes the shape you want. To use a shape from the library: 1. Select the particle type in the Workspace panel. 2. Click Shape to show the Shape controls. See Shape Controls. 3. Select a shape in the shape library. The shape appears in the shape viewer. 4. Click Swap. If the Particles preview is enabled, you can immediately see the shape in use. Using Operators for Shapes If there is an image or image sequence in the workspace that you want to use as a shape, you can use it (or a small portion of it) as the shape. You can crop the shape, resize it, and select the source channels and color depth. An advantage of this method is that you can use images that are already processed (for example, keyed and color corrected). ▲ Since multi-frame shapes use a lot of memory, do not use an entire clip unless you need to. Likewise, do not use a full-resolution source operator for a shape. The Particles operator always needs random access to all frames, so it stores the entire range of frames in memory at full resolution. This, in turn, can affect the performance of the Particles operator. Often one or a few frames is enough for the effect. If you only want one frame and the operator has many frames, save (render) the image, and then import the shape instead. 368