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If you've ever tried to render a forest of trees in actual polygons whether it be in Bryce, DAZ Studio, Carrara or any other program, you're bound to have noticed that with each tree added, rendering time increases exponentially. Here's a quick and easy trick to sidestep all those polygons, without losing that visual feel of density that you're probably looking for in your scene.
Using a 3D rectangle smushed flat, or if the option is available, using a 3D plane, insert this object into your scene.
Using the texture options in your program, texture the plane with any picture of a tree - preferably one that has been masked against a solid background as shown.
Using an inverted grayscale of the same image you used to texture the sprite, set this as the new map for the transparency of the sprite.
Give your sprite a preview render to see how it looks and make sure that you have all the transparency settings on your texture adjusted correctly - if successful it should look something like this.
To give your sprite more of a 3D feel, copy the rectangle / plane and rotate the copied sprite 90 degrees for a bi-planar sprite, rotate two 60 degrees for a tri-planar sprite, three 45 degrees, and so on.
When rendering, be sure to select “Render through transparencies” or some similar feature to ensure that shadows will be casted through the transparency map that you applied. Saturate your forests now with these sprites in the background, add a few high-poly 3D trees towards the front, and voila: render efficient forests!