Animation

Introduction

Almost every computer graphics application includes some form of a feature that allows creating animation. Most of them use the concepts invented by the first creators of "cartoons" drawn on paper and adapted to computers as time went on. Blender isn't too different in this regard. Nevertheless, 3D animation includes some extra concepts not present in 2D, such as: skeletons and IK (very rarely present in 2D), objects constraints in 3D using special rules and most of all advanced physics engines operating in a 3D environment. This exercise, just like the previous, will demonstrate only the basics, but it will also contain references to more information about animation in 3D graphics.

Keying

The simplest form of animation available in most graphic suites is through the concept of "keyframes". This idea stems from the early days of paper and cel animation. There you would initially design they most important, or "key" frames and then fill the rest in such a way to make the whole motion as realistic as possible.

Computers made the whole process considerably simpler, since they allowed for generating most of the non-key frames completely automatically. Another difference was that (especially in 3D animation) we generally tend to manipulate actual objects (ie. vectors), rather than redraw each frame from scratch.

In Blender we can "key" almost any value in the program. The keyboard shortcut I (capital letter i, not L!) lets us add a "key" for a given value in the current frame of animation. It is often sufficient to simply hover the mouse over a value in the program and press I, which will allow us to animate it in time (some values, e.g. resolution, cannot be animated, for obvious reasons).

Camera motion (task for grade 3)

One of the basic uses of animation in Blender is to control the camera. Even if we have a static model in 3D (eg. a monument or a piece of architecture), adding camera animation can greatly improve the attractiveness of the work and increase its realism. Let us therefore start with a simple scene:

• move the default cube to location (0,0,1)
• add a Plane to the middle and scale it 100 times
• change the default light to a Sun lamp

Now select the camera (eg. from the object tree, top right corner of the window) and enter the camera view (by pressing 0 on the numeric keypad). We want to make a flyby with the camera over the top surface of the cube. Let's start with positioning the camera at a certain distance from the cube (as a reminder, this is easiest to achieve by pressing SHIFT-F followed by using the mouse and the A,W,S,D,Q,E keys). After positioning the camera, make sure you are located in the first frame of the animation. Look at the timeline at the bottom of the screen and make sure the time cursor is all the way on the left. You can also use the shortcut SHIFT-← (shift followed by the left arrow) to rewind the animation. Now move the mouse cursor over the 3D view and press I on the keyboard. A menu will appear with a list of items you can create keys for. Since we are only going to change the location and rotation of the camera, simply choose LocRot from that list.

We have thus set the first key frame of our animation. Now move the time cursor to the frame #100 and move the camera to its next position - preferably somewhere close to the cube. Press I again (remember to keep the mouse over the 3D view when you do that) and set the next LocRot key frame. Move to frame #150 and change the camera to yet another location - on the other side of the cube but still pointing towards it and add another key frame. Finally, change the frame to #250, move away from the cube a little bit and and add the last key frame. Playing it back, you should see something like this:

To play it back, you need to rewind the animation (SHIFT-←) and press the play button (or the keyboard shortcut ALT-A).

By clicking on the little clock icon in the lower left side of the timeline, you can change the view to the Graph Editor. This is an alternative method for viewing and editing the key frames. If you want, you can use this view to fine tune your camera motion.

Following a path

(task for grade 3.5)

A simple way to add motion is to move an object along a path. This can be done using keying and the graph editor, but there is a simpler way. Lets start by drawing a curve:

• add Curve/Bezier object to the scene and translate it 2 units in the up direction (so it lays flat on top of the cube)
• go to the top view (7 on the numeric keypad) and turn on the orthogonal view (5 on the numeric keyboard)
• enter Edit mode and select one of the vertices
• move it to a location (G key) and use rotation (R key) and scale (S key) to change the control points
• to add a new point use the E key
• add a couple of points to create an (almost) closed shape
• click Toggle Cyclic in the menu on the left

Later you can come back and fix some of the points you created earlier and even delete them with the X key. The final curve should look something like this:

Now let's add an object that moves along this curve:

• press 2 on the text keyboard (above the letters) to switch to the second layer of the scene - everything will vanish for a second, but don't worry, it's just temporary
• press SHIFT-C to center the scene and add some mesh to it (eg. Cone or Monkey)
• raise it by 0.25 units up and scale it down 4 times (scale by 0.25) - you can also rotate and refine its location as long as it's hovering slightly above the surface
• press CTRL-A and choose Location and then CTRL-A again, but this time choose Scale - this way we can apply the sizes and location of the mesh in the scene - in the Object Data tab (the icon of a cube in the menu on the right) you will notice the location will be 0 and scale 1, even though we changed it
• no go to the Object Constraints tab (with the icon of two chain links) and add a constraint called Follow path (from the Relationship list, all the way to the right) - initially it will be marked red
• choose the curve you created from the list at the parameter named Target - the mesh will be immediately moved to the location of the curve and the constraint will not be red anymore
• the object is located correctly, but it not moving with the animation - click the Animate Path button to automatically generate an animation along the path

You can play the animation now and observe the motion of the mesh along the curve. Let us combine it with the rest of the scene now:

• while only the mesh is selected, press M (as in move) and the number 1 (on the text keyboard, above the letters) to move the mesh to the first layer
• press 1 to display the first layer

After playing, the scene should look like this:

Physics simulation

Blender contains a pretty advanced physics engine called Bullet, which can be used also outside of Blender (available as an SDK in many languages). In Blender, we can perform all sorts of different physics simulations like, rigid body, soft body, cloth, liquid, smoke and fire, etc. Some of them are more complicated than others. For example, liquids are fairly easy to create in a basic form, but very difficult to make it look perfect and also requires a lot of processing power. Smoke and fire are types of effects that are difficult to capture on a camera in real life, let alone Blender. For this lesson, we will demonstrate two simplest types of physics simulations.

Rigid body (task for grade 4)

Rigid body is the simplest (and oldest) form of physics simulation you can do in Blender. Rigid bodies are divided into two categories:

• passive - constantly fixed in space and motionless, but participating in the simulation by enacting forces (as barriers) unto active bodies
• active - normal objects participating in the simulation, with all forces acting upon them (including gravity)

There is also a third type - objects not being part of the simulation at all. They can be rendered and visible, but all rigid bodies will completely ignore them. Let's start by modifying our scene slightly:

• select the cube in the scene, open the Physics tab in the menu on the left and click Add Passive
• select the ground (the plane) and do the same
• now select the object that is moving along the path and choose Add Active for it - we don't want to enact any forces on it directly (because it is already animated), but since it's not motionless, we will mark it as active
• now go to the Physics tab in the menu on the right (icon of a bouncing ball, all the way on the right) - notice that after we added the Active property, the object has a little cross next to the Rigid Body and Active selected in the options below
• mark the Animated checkbox - this way we solve the animation issue
• now add a different mesh (preferably flat), e.g. a Torus and put it somewhere in the air, above the cube
• click on the Rigid Body option in the physics tab and make sure it is marked as Active

If you rewind the animation (SHIFT-← ) and play it back (ALT-A) you will notice that the object is falling according to the laws of physics. What's neat is that you can also duplicate it as much as you want (SHIFT-D - the animation below has about 30 objects) and all of them will behave the same way:

Rigid Body simulations are very interesting and can be used to achieve a lot of cool effects. A common demonstration are demolishing constructions (e.g. buildings, bridges). This can be improved by adding various constraints between objects - solid, breaking and even springs. Another nice example are chains: with a little bit of work, you can use this method to create a simulation of a whole chain or even chain mail armor. The final neat example are various clock mechanisms and Rube Goldberg machines: if we create a models of gears of specific shapes and sized, they should behave like actual, real-life objects. Of course, at a certain point, the physics simulation may break down and not be able to recreate the actual conditions from the real world. We can improve the accuracy of the simulation (at the cost of processing power) in the scene options (tab with an icon with three tiny object, third from the left), in the Rigid Body World section. This won't be discussed in detail on this lesson.

Cloth (task for grade 4.5)

Another neat and simple physics example is the cloth simulation

• add a Plane mesh to the scene, put it 50 units above the ground and scale it 5 times - we are putting it so high, so that is falls slowly on top of everything only in the second half of our animation
• enter edit mode (TAB key) and choose Subdivide about 5 times (but not more!) - it's in the menu on the left in the Tools tab
• exit Edit Mode (again using the TAB key) and go the the physics tab in the menu on the right (the one with the bouncing ball)
• click on the Cloth button and notice the options below
• in the Cloth Collision section, check Self Collision and also change the Distance parameter (the one on the left) to 0.1 - this will make sure that the meshes don't peek through the very thin fabric
• now select all the objects that should interact with the fabric, and add the Collision property from the Physics tab (directly above Cloth)

The objects mentioned in the last point should definitely include the cube, the ground, but also anything else that is in motion and comes into contact with the fabric. If you rewind and play the animation now, you should see a convincing looking fabric falling from the sky. First time you run the animation, it may work a bit slow, but after it is cached, it should run completely smoothly. In the end, you can add to the fabric a Subdivision Surface modifier (CTRL-2) and change the shading to Smooth. The final result should look something like this:

Render

(task for grade 5)

To get the highest grade, you need to improve the above scene (add materials and lights) and create a final render. Rendering an animation isn't much different from rendering an image, but takes much longer (actually, exactly 250 times longer in this case). Check the following settings in the Render tab (the camera icon, first in the menu on the right):

• set the percent value under resolution to 25% - this will greatly speed up the process, but will reduce the resolution 4 times
• the output section should contain a path, e.g. to a file with the extension AVI
• the format should be changed from PNG to something that can store animations (e.g. H.264)
• make sure to tweak the colors, textures and lighting so that your work is unique and amazing!
• after setting everything up you have to click Animation next to the Render button

And now you need to wait. It is very likely this task cannot be finished on the lesson. That is why this is the only exercise you can finish at home and bring the final (original!) movie to the next lesson. Just to be sure, don't forget to show the teacher your final progress before leaving the classroom.