The Velcro (formerly Farseer) Physics Engine is a .NET library which can be used to add more advanced physics beyond what is offered by FlatRedBall's shapes (such as Circle or Rectangle). Note that the Github page for Velcro states that sponsorship is required to use Velcro Physics in a commercial project, so consider this if you plan on selling your game.
In general, the following must be done to use Velcro Physics:
Instantiate a World object
Call the World instance's Step function every frame
Create one or more Body instances - A Body is created through Velcro's Factory classes. The Body must be added to the World.
Set properties on the Body instances - You can set properties such as size, orientation, velocity, and how the bodies respond to collisions (inertia, elasticity, friction).
This demo will create two Body instances which will perform the physics simulation. It also creates a FlatRedBall Circle and Polygon to display the visuals of the Velcro bodies.
To add Velcro to your project:
Expand your game project's Dependencies
Right-click on Packages and select Manage NuGet Packages...
Check the Include prerelease option
Search for GenBox.VelcroPhysics.MonoGame
Add the Genbox.VelcroPhysics.MonoGame package to your project.
Once you have added Velcro to your project, you can begin using the classes to perform physics simulations. The following is example code which could be added to a GameScreen to create a simple Velcro simulation:
This walkthrough shows how to add Velcro to a simple FlatRedBall project. We will create a diagonal stack of blocks which will fall and collide against a static surface. This tutorial uses the FlatRedBall desktop engine, which means it uses proper XNA (as opposed to MonoGame). MonoGame projects must use the MonoGame version of the Farseer .dll.
We will begin with an empty FlatRedBall project:
Add a new Block entity:
Right-click on Entities
Select Add Entity
Enter the name Block
Click OK
Next, we'll add a Sprite to the Block so we can see it in-game:
Expand the Block entity
Right-click on Objects
Select Add Object
Select Sprite
Click OK
The Sprite needs to be modified so it will show up in game:
Change the Sprite's Color Operation to Color. This allows us to use solid colors to draw the sprite instead of a texture.
Set the Red value to 1
Delete the Texture Scale value
Enter a Width of 32
Enter a Height of 32
Next we'll create a screen to hold our Block instances and the Farseer logic:
Right-click on Screens
Select Add Screen
Enter the name Game Screen
Click OK
GameScreen needs a Block list so that we can construct the blocks in code and have them be automatically managed. To do this:
Push and hold the right mouse button on the Block entity
Drag the entity onto GameScreen
Release the mouse button
Select Add Entity List
Now that our Glue project has been created, we'll add Farseer to the Visual Studio project:
Download the Farseer precompiled .dll: https://github.com/vchelaru/FlatRedBall/blob/master/Engines/FlatRedBallXNA/3rd%20Party%20Libraries/Farseer/FarseerPhysics%20XNA.dll?raw=true
Open the game project in Visual Studio
Right-click on References in Visual Studio under your game project
Select Add Reference...
Click the Browse category
Click the Browse... button
Navigate to where you saved the Farseer dll file
Select the file and click Add
We'll add the code to create a Farseer Body instance in the Block.cs file. Open the Block file and modify the class so it appears as shown in the following code:
Finally we'll add code to our GameScreen . Modify your GameScreen.cs file so it looks like the following code:
If we run the game we'll see our blocks falling and colliding: