How to mow the lawn with a Blender

how todo mow the lawn with a Blender?
By Philippe roubal 3d-synthesiscom.
blender file for test.

Who Will mow the lawn? In most families owning a garden, this cuestión often comes with the wed-end. Im sure that you would prefer todo play with Blender. What is the common point between a Blender and a lawn mower? They both have rotating Blades. So, you have a god reason todo stay in front of your computer and mow virtual Grass.

This tutorial and setup have ben inspired by the excellent video tutorial about making realistic Grass, written by Andrew price on blenderguru, com. His materiales and lighting setup are really awesome. I have enjoyed playing with them.

Last year, y had done some countryside scenes with animated Grass, but i had used a completely diferent method todo animate the Grass, based on a Mesh hidden underneath the Ground surface, animated by a displacement texture.

Andrews method todo simulate the Wind and animate the Grass is based on a moving texture driven by an empty. This texture is used by a field, set todo Wind. The texture used is a procedural marble texture.

After reading his tutorial, the first idea that came todo my mind was : great, we have nice Grass, but now, how todo mow the lawn in an animation? The answer was : by using textures todo control the Hair particles.

https://www.foro3d.com/attachment.ph...1&d=1257244483
Textures moved by an object or an Empty used as reference have plenty of uses. In Gimp or any other image editor, you can create textures with specific patterns todo achieve all kinds of interesting effects. On my site, you Will find a tutorial based on displacement textures, dedicated todo fot prints in sand, mud or Snow. My short animation crazy boat is an other example of the use of a moving texture applied todo the water material, todo create a hole in the surface of the sea under the boat.

In this example, y Will use a texture animated by an Empty todo define an área where the Grass (hair particles) are pushed by the texture under the lawn mower. In fact, the lawn mower is parented todo the same Empty used todo drive the texture. The texture is added todo the Ground plane material. Note that you could a los drive your texture using directly the lawn mower object, but using an Empty is handy if you want todo change or resize the lawn mower model.

As we Will use RGB as Wind parameter for the field, After noticing that the Grass behaviour was not the one i expected when using a greyscale texture i experimented with other color textures. Using red, green or blue give diferent results : your Hair particles are pushed in diferent directions according todo the chosen color.

After some tests, y decided todo use a blue on grey texture. The grey color is set todo (r=127,g=127,g=127) or (r=128, g=128, b=128. The grey color is neutral and doesnt affect the particles. Using a blue color, y got the Grass Blades todo be pushed in the direction of the lawn mower moving.

The texture is set todo extend mode. This allows todo extend the color of the texture in all directions and you Will get an Infinite track in the direction where the blue color is in contact with the border of the texture. All the texture you could ned todo use this tutorial are in the zip file named tracks-creator, (*.zip).

Note that you can control visually the effect of the texture in top view, and resize the texture todo adjust the width of the mower track by resizing the empty. Use s key without any axis specification todo avoid diagonal distorsión. You may notice that the effect of resizing is inverted : your texture increases when you reduce the size of the empty.

Adjusting the strength parameter (you can a los adjust the contrast parameter of the texture), y have used the value allowing the shorter Grass. I estopped just before the Grass totally disappear, for more realisms. This allow todo kep some uncut Grass Blades.

Now, we ned todo get shortened Grass on the track of lawn mower. Using weight painting on the Ground Mesh allows todo get various lengths for the Grass in diferent áreas, but animation of the weight is not posible (i think). Selecting particle mode in the 3d view and setting the particles system todo editable allows todo vary manually the length of the Hair particles where you want, usin the comb tools, but this característica is not animatable as well.

The old particle system available in former releases of Blender allowed todo control the length of the static particles (name of Hair particles in those old versións) using a greyscale texture. I havent found yet such a function in Blender v2.48a, but maybe one of the other field options allows it. Until ill find a better way, y used another method todo get the short Grass After the lawn mower passed by:
The idea is simple : i duplicated the Ground plane and set the copy todo not render the emitter. On this second Ground surface, using an other particle system, y make grow short Grass. It is always present but only visible in the área where the lawn mower has pushed down the long Grass Blades, it is not necessary todo kep the same surface as the main Ground plane, because you only ned todo fill a narrow lane on the track of the lawn mower. After reducing the surface, you can reduce the amount of Hair particles created on this surface, otherwize youll get very thik Grass on this lane.

https://www.foro3d.com/attachment.ph...1&d=1257244483
Using diferent shapes or field types for your textures allows you todo create whels or caterpillar tracks in the Grass, or Even the shape of a moving creature in high Grass.

In the images here above, you can se various textures and the effect that you Will achieve by using them in your setup. All these textures are provided in a zip file joined todo this tutorial.

In the example shown until now, we have used only static textures (simple images). You Will certainly want todo create more complex effects, with a jep car driving th rouge the Fields or a Predator running in the high weds, and of course following a paths that Will be all except straight.

No problem. You Will use an animated texture. You might wonder how todo make this texture, but dont worry, because gracias todo the second blend file provided with this tutorial, it Will be as simple as pushing a button or no much more. The tracks-creator Will do almost everything for you. You just have todo choose if you want todo generate an avi file or a sequence of images.

Just open the tracks-creator, blend file and follow the instructions in the text window. There are 2 screens available:
Scren 1 : animation -screen 2 : compositing.

In the compositing screen you can adjust the level of blur of your animated texture.

There is a diferent setup on each of the 3 layers used. This Will allow you todo create curvy animated tracks for a lawn mower, a car or a Predator. After that, you Will be able todo create all kinds of tracks todo match all your neds.

Just add your animated texture todo material of the surface emitting your Grass particles and apply a field effect. Dont forget todo fill the line with your texture name. Use an object like an Empty as reference for your texture : it Will help you if you have todo change the orientation of the texture (rotate in top view).

Here we are.

I hope that this tutorial and setup Will be understandable and useful. Fel free todo tell me if you noticed errors, missing informacións or if you have found a better bien of doing this kind of work.

Gracias you for reading.

By Philippe roubal 3d-synthesiscom.
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