HowTo_Create_a_BasicEffect.md

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How to create a Basic Effect	Demonstrates how to create and initialize an instance of the BasicEffect class and use it to draw simple geometry.	true

Overview

The steps described here apply to effects created with the BasicEffect class using the Effect class to write a custom effect.

Note

The example draws aliased geometry, to see an example that draws smoother edges because it also applies anti-aliasing, see Enabling Anti-aliasing (Multi-sampling).

End result

To use BasicEffect

Using the basic effect class requires a set of world, view, and projection matrices, a vertex buffer, a vertex declaration, and an instance of the BasicEffect class.

1. Declare these properties at the beginning of the game class.

   //Matrices for 3D perspective
   private Matrix worldMatrix, viewMatrix, projectionMatrix;
   
   // Vertex data for rendering
   private VertexPositionColor[] triangleVertices;
   
   // A Vertex format structure that contains position, normal data, and one set of texture coordinates
   private BasicEffect basicEffect;

2. Initialize the world, view, and projection matrices in the Initialize.

   Next, create a world matrix using the default Matrix.Identity for simplicity. Set the view matrix as a look-at matrix with a camera position of (0, 0, 50), pointing at the origin. The projection matrix is a perspective projection matrix based on a a 45-degree field of view, an aspect ratio equal to the client window, and a set of near and far planes to render the geometry within in view of the camera.

   protected override void Initialize()
   {
       // Setup the matrices to look forward
       worldMatrix = Matrix.Identity;
       viewMatrix = Matrix.CreateLookAt(new Vector3(0, 0, 50), Vector3.Zero, Vector3.Up);
   
       projectionMatrix = Matrix.CreatePerspectiveFieldOfView(
           MathHelper.PiOver4,
           GraphicsDevice.Viewport.AspectRatio,
           1.0f, 300.0f);
   
       base.Initialize();
   }

3. Initialize a BasicEffect with the transformation and light values in the LoadContent method.

   protected override void LoadContent()
   {
       basicEffect = new BasicEffect(_graphics.GraphicsDevice);
   
       basicEffect.World = worldMatrix;
       basicEffect.View = viewMatrix;
       basicEffect.Projection = projectionMatrix;
   
       // primitive color
       basicEffect.AmbientLightColor = new Vector3(0.1f, 0.1f, 0.1f);
       basicEffect.DiffuseColor = new Vector3(1.0f, 1.0f, 1.0f);
       basicEffect.SpecularColor = new Vector3(0.25f, 0.25f, 0.25f);
       basicEffect.SpecularPower = 5.0f;
       basicEffect.Alpha = 1.0f;
       // The following MUST be enabled if you want to color your vertices
       basicEffect.VertexColorEnabled = true;
   
       // Use the built in 3 lighting mode provided with BasicEffect            
       basicEffect.EnableDefaultLighting();
   }

   [!NOTE] If you wish, you can set up the lighting manually through code, as follows: [!code-csharp]

4. Still in LoadContent, create the per vertex data using the VertexPositionColor format. This example shows the data for the face of a triangle.

   triangleVertices = new VertexPositionColor[3];
   
   triangleVertices[0].Position = new Vector3(0f, 0f, 0f);
   triangleVertices[0].Color = Color.Red;
   triangleVertices[1].Position = new Vector3(10f, 10f, 0f);
   triangleVertices[1].Color = Color.Yellow;
   triangleVertices[2].Position = new Vector3(10f, 0f, -5f);
   triangleVertices[2].Color = Color.Green;

5. Finally, in the Draw Method, call GraphicsDevice.Clear to clear the render target.

6. Set the rasterizer state to turn off culling using the RasterizerState property.

7. Call EffectPass.Apply to set the effect state in preparation for rendering.

8. Draw the geometry by calling GraphicsDevice.DrawUserPrimitives.

   protected override void Draw(GameTime gameTime)
   {
       GraphicsDevice.Clear(Color.SteelBlue);
   
       RasterizerState rasterizerState1 = new RasterizerState();
       rasterizerState1.CullMode = CullMode.None;
       GraphicsDevice.RasterizerState = rasterizerState1;
       foreach (EffectPass pass in basicEffect.CurrentTechnique.Passes)
       {
           pass.Apply();
   
           GraphicsDevice.DrawUserPrimitives(
               PrimitiveType.TriangleList,
               triangleVertices,
               0,
               1,
               VertexPositionColor.VertexDeclaration
           );
       }
   
       base.Draw(gameTime);
   }

When the sample is run, the basic geometry is rendered using the custom BasicEffect, feel free to play with the position, content or rendering order to enhance the effect.

See Also

• How to create a State Object

Concepts

• What Is a Configurable Effect?

Reference

• GraphicsDevice
• BasicEffect
• RasterizerState