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GET A TASTE OF THE GRASS FEATURE
Get a taste of the Grass feature


The Grass Primitives

The guide curves created and distributed by the Grass Generator have to be replaced by a renderable geometry in order to present an actual surface that can handle a material description and be renderable. This happens at the beginning of the render, when the guides in the MXS file are replaced by one of the following Grass Primitives, that define the shape of each blade of grass.

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As this primitive is made of an analytic curved surface, it is smooth at each point, no matter how close you look at it. This means you don't need to increase the number of points too much to get a smooth blade. In general, using around 4-6 points per blade is enough to perfectly define the smooth shape, without using too much RAM during rendering. Many more points than this is not necessary for the Curve primitive and will only increase the RAM usage without adding anything to the look of the blade.

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Note

The Curve grass primitive is slower to render than the Flat primitive. For this reason, we suggest to always use the Flat primitive for the fastest renders and if the camera needs to be very close to the grass blades, use a separate smaller patch of grass that's close to the camera and use the Curve primitive for this patch.

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As you can see, there are many different options to map the grass surface, combining these two UV channels. Similar to the example above, you can also map a Layers weight with a texture and set it to use UV channel 1. The BSDFs contained in this Layer can in turn have textures using UV channel 0 (root to tip) which are different from the textures used in the BSDFs of the bottom Layerlayer, and also use different material settings such as thin SSS settings. And why not above these two Layers, add a third one, with a simple color texture (using channel 1) and set the layers layer's weight very low just to add even more subtle color variation across the grass surface.

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Randomize the length of each blade, specifying the range of possible length values as a percentage of the nominal Length parameter. For example, if Length is set to 10cm and Length variation is set to 50%, the length of the blades will be randomized between 5cm and 15cm.

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Randomize the growth angle by a percentage of the initial angle variation. For example, if the initial angle is set to 70 degrees and variation is 10%, the angle will be randomized between 63 and 77 degrees.

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Tip

For a tutorial on creating an angle map in Photoshop, see the Grass Tutorials page in the Tutorials section. Two Photoshop actions are also available on that page to automatically create an angle map from a black & white drawing.

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