Monday, January 18, 2010

BGE Blender 2.50 Part 1

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This is the first in a series of tutorials on the Blender Game Engine (BGE) in Blender 2.5. The purpose of this tutorial is a quick tour of the BGE user interface in 2.5. If you have used the BGE in 2.4x, the process should be fairly familiar to you. Even if you have never used the BGE, after watching this tutorial you should be comfortable enough to experiment with creating more complicated games. I'm using Blender 2.5 Alpha 0, which you can download from

So let's get started. We'll use the default cube, in the default scene. We're going to bounce the cube onto a plane, simulating the ground. To create the plane, press Shift-A, then Mesh, then Plane. Scale the plane 10 times (S - 10 - Enter). Position the plane so that its center is roughly at the center of the cube. Select the cube. Move the cube upwards, in the positive Z direction, about 5 blender units, by pressing the G key, then the Z key, then 5. Now the cube appears to be ready to be dropped.

Blender 2.5 contains a series of views that are designed for things you would commonly want to do. Click on the icon to the left of the Default text. You should see selections such as Animation, Compositing, Scripting, and so on. Select Game Logic. Let's do a litte tour of the Game Logic setup. At the upper left is the outliner. In addition to the Camera and the Lamp, we have the cube, which is the active object, and the plane, which is just called Mesh. To the right of the outliner is the 3D view, set to Top View to start. Let's change to front view and rotate the view a bit so that we can watch the cube drop. With the cursor inside the 3D view, press Num1, or from the View Menu select Num1, to go to Front View. I used the middle mouse button to give the view a bit of an angle from the Front View, so you can see the cube drop.

Blender's game engine uses the Bullet Physics library to simulate gravity, collisions, bouncing, and the physics of the game world. This is actually a different type of physics library than, say, the fluid simulator or soft bodies. One of the challenges of working with the game engine is getting used to the differences. Animation and texturing, as examples, work a bit differently in the BGE than in the 3D modeling part of Blender.

Having said that, to make the cube participate, so to speak, in the game, we need to select the cube and click on the Physics buttons (all the way to the right). Right now, the settings for the BGE are not available to us. It appears as if the 3D physics options, such as Fluid and Cloth, are what's available. To make the BGE settings active, change the the renderer from Blender Render to Blender Game. Now the Blender Game Physics options can be set. To make the cube do its thing in the game engine, change the Physics type to Rigid Body. Note that the Actor check box is checked automatically.

This is enough to make the cube participate in the game. As in 2.4x, with the cursor in the 3D window, press the P key to start the Game Engine. The cube falls onto the plane, and rolls over a bit. Press ESC to go back to the 3D view.

Another way to start the Game Engine is to click on the Camera icon, the first one on the left, in the Properties Window. The buttons here also changed when we changed the view from Blender Render (which shows the image and animation settings) to Blender Game. Now, there's a big Start button. We can press the Start button to start the game as well.

Now we're going to add some interactivity to the game. We'll push the cube to the edge of the plane by nudging it a bit, until eventually the cube falls off into oblivion. To do that, we'll work with the bottom middle window. We'll maximize this window by pressing Control - Down Arrow. Then we'll zoom, using the Num- key, until we can see the Sensor, Controllor, and Actuators button groups. There are 3 Add keys. Click each Add key to add a Sensor, a Controller, and an Actuator. Here's the deal. The Sensor looks for some type of activity, in this case it's going to look for a particular key to be pressed. The Controller can control the logic as to what happens when that key is pressed. The Actuator determines what exactly happens after the sensor and controller logic has been set.

Let's make it so that when the user presses the R key, the cube moves a bit in the X direction. To do that, click on the Always dropdown in the Sensor area. Note that there are all types of sensors. We're going to use the Keyboard sensor. Select Keyboard. Position the mouse at the Key area, and left click. The prompt Press A Key displays. Press the R key. Any key will do.

Now go to the Actuators area. In the first Loc area, enter 0.5. The idea is that when we press the R key, the cube will go .2 Blender Units in the X direction. If you had entered 0.2 in the second area the cube would go .2 Blender Units in the Y direction, and similarly 0.2 in the 3rd area would make the cube go .2 Blender Units in the Z direction. There are other things you could have made the cube do, such as add a force or rotate (torque).

Finally, we need to hook up the Sensor, Controller, and Actuator. Connect the right socket of the Sensor with the left socket of the Controller. Then connect the right socket of the Controller to the left sockete of the Actuator. Now, when the BGE detects the R keypress, the cube will go .2 Blender Units in the X direction.

Let's see if this is what happens. Press Control-down arrow to return this logic window back to its original position. Click the Start button. The cube does what it did before. Now I will press the R key a few times. The cube bounces up a bit because that's what the Bullet Physics calculation might think a cube resting on its point might do as well. Eventually, the cube falls off the plane and bounces into space.

Let's add some more interactivity. Add an icosphere next to the cube (Shift-A, Mesh, Icosphere), accepting the defaults. Position the icosphere under the cube, between the cube and the plane. Go to the Physics tab. Give it a Rigid Body physics preoperty. Let's make the icosphere go .2 Blender Units in the -Y direction when we press the Space Bar. Maximize the bottom middle window, the one with the Sensor, Controller, and Actuator tabs. Press the 3 Add buttons for Sensor, Controller, and Actuator. Select the Keyboard sensor. Move the cursor to the Key area and left click. When prompted to press a key, press the Space Bar.

Press the P key in the 3D window to start the game. If you positioned the icosphere underneath the cube, watch the cube hit the icosphere and then react as if it was affected by the collision. Depending on how large the plane is and how big the cube and icosphere are, you might get different effects. The cube and or the icosphere might fall off the plane. Pressing the space bar causes the icosphere to move.

I hope this gives you a start with using the Game Engine in Blender 2.5. Press the SUBSCRIBE button on Youtube to make sure you won't miss my future BGE and Blender tutorials. Happy Blendering!