How many BasicEffects do you have in a Game? What is the best way to render multiple objects/shapes at once?

Question

I'm trying to understand 3D rendering and it seems that everytime you render a new object (A 3D Cube or something) you need to have a new BasicEffect for each Box you render unless you want the exact same texture?

...so if I have over a hundred boxes with each different textures, I need at least as many BasicEffects? Will that not be "too much" for the CPU/GPU in the end or result in lagging? Is there any good way to render multiple objects (cubes or other shapes) at the same time?

I've tried changing the BasicEffect.Texture with each cube drawn, but it resulting in changing the first Cube's texture too.

Any suggestions would be really appreciated, I'm really new to 3D in XNA so I'm trying to wrap my head around the best methods for example render a Map with objects (of shapes).

Example: I create some Cube3D (by providing location and size) and it creates a list of Vertices.

I have to render it this way:

            gameEffect.TextureEnabled = true;
            gameEffect.Texture = gameTexture;
            gameEffect.EnableDefaultLighting();

            foreach (EffectPass pass in gameEffect.CurrentTechnique.Passes)
            {
                pass.Apply();
                foreach (Cube3D cube in gameCubes)
                {
                    cube.Render(GraphicsDevice);
                }
            }

...thereby having the same Texture on each Cube. Are there any other ways?

Answer 1

For drawing multiple objects in XNA you can have one or multiple effects.

If you have only one you must set all parameters (texture, light color, light direction...) for each object before drawing it. All common values for all objects (view and projection matrix for example) can be set once at the beginning of drawing.

If you have multiple effects. For each object exactly one instance. You must set only that parameters that are changing (view and projection matrix, etc..) each frame.

Definitely is not good to create new BasicEffect or load custom effects in Draw method. Create it in Load method.

There are also another method how to draw models in XNA. BasicEffect is actually a shader and you can write your own. Something more about shaders and how to use them you can read here: http://digitalerr0r.wordpress.com/tutorials/

Answer 2

Unless i am missing something i think that XNA approach is flawed. You shoud have something like this:

class Model
{
   public List<Material> Materials;
   public ModelMesh Mesh;
}

and Model should be created in game by new Model(Content.Load()) and not cached (or loaded by some alternative from xml). Materials should be collection of parameters that you pass to effects inside Mesh.MeshParts[].Effects (like texture)

Answer 3

It's actually simpler to embed the texture reference with the model itself. That way, when you load your model via the content pipeline, the texture is loaded with it automatically. This thread has some information on that:

http://www.dreamincode.net/forums/topic/227811-how-do-i-put-a-texture-to-a-3d-model/

Then when you draw your scene, you can loop through your models something like:

protected override void Draw(GameTime gameTime)
{
    graphics.GraphicsDevice.Clear(Color.CornflowerBlue);

    // Copy any parent transforms.
    Matrix[] transforms = new Matrix[myModel.Bones.Count];
    myModel.CopyAbsoluteBoneTransformsTo(transforms);

    // Draw the model. A model can have multiple meshes, so loop.
    foreach (ModelMesh mesh in myModel.Meshes)
    {
        // This is where the mesh orientation is set, as well 
        // as our camera and projection.
        foreach (BasicEffect effect in mesh.Effects)
        {
            effect.EnableDefaultLighting();
            effect.World = transforms[mesh.ParentBone.Index] * 
                Matrix.CreateRotationY(modelRotation)
                * Matrix.CreateTranslation(modelPosition);
            effect.View = Matrix.CreateLookAt(cameraPosition, 
                Vector3.Zero, Vector3.Up);
            effect.Projection = Matrix.CreatePerspectiveFieldOfView(
                MathHelper.ToRadians(45.0f), aspectRatio, 
                1.0f, 10000.0f);
        }
        // Draw the mesh, using the effects set above.
        mesh.Draw();
    }
    base.Draw(gameTime);
}

This tutorial might help you make sense of loading and drawing 3D models with XNA:

http://msdn.microsoft.com/en-us/library/bb197293(v=xnagamestudio.31).aspx

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If you are going to render your own primitives in code, I don't know any other way to apply a texture than a BasicEffect. If Cube3D is your own class, I'd suggest adding a BasicEffect and a Texture2D to the class. That way, you can supply the texture to the Cube3D constructor and it setup the BasicEffect for you. If it's not, you could extend it.

class Cube3D {

    ...
    public BasicEffect Effect { get; set; }
    public Texture2D Texture { 
        get { return Effect.Texture; }
        set { Effect.Texture = value; }
    }
    ...

    public Cube3D( Texture2D t ) {
        ...
        this.Texture = t;
    }

    ...
}

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It seems as though you can also use the Effect class to apply a texture as well:

http://www.riemers.net/eng/Tutorials/XNA/Csharp/Series2/Textures.php