Procedural geometry

In this example, we delve into creating procedural geometry meshes including a triangle, a plane, and a circle, and integrate them into a Stride scene. Utilizing the MeshBuilder class from the toolkit, the process of crafting and rendering these geometries is streamlined.

The MeshBuilder class is employed to define the layout and data for each mesh. For instance, the GiveMeATriangle, GiveMeAPlane, and GiveMeACircle methods demonstrate how to configure vertices, indices, and other properties to form a triangle, a plane, and a circle, respectively.

The Update method demonstrates a dynamic adjustment to the circle's segments count over time, showcasing a simple animation effect.

For more details of MeshBuilder, refer to our MeshBuilder manual.

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using Stride.CommunityToolkit.Engine;
using Stride.CommunityToolkit.Rendering.Utilities;
using Stride.CommunityToolkit.Skyboxes;
using Stride.Core.Mathematics;
using Stride.Engine;
using Stride.Games;
using Stride.Graphics;
using Stride.Rendering;
using Stride.Rendering.Materials;
using Stride.Rendering.Materials.ComputeColors;

using var game = new Game();

Entity? circleEntity = null;
game.Run(start: Start, update: Update);

void Start(Scene rootScene)
{
    game.SetupBase3DScene();
    game.AddSkybox();

    AddMesh(game.GraphicsDevice, rootScene, Vector3.Zero, GiveMeATriangle);
    AddMesh(game.GraphicsDevice, rootScene, Vector3.UnitX * 2, GiveMeAPlane);
}

void Update(Scene rootScene, GameTime gameTime)
{
    var segments = (int)((Math.Cos(gameTime.Total.TotalMilliseconds / 500) + 1) / 2 * 47) + 3;
    circleEntity?.Remove();
    circleEntity = AddMesh(game.GraphicsDevice, rootScene, Vector3.UnitX * -2, b => GiveMeACircle(b, segments));
}

void GiveMeATriangle(MeshBuilder meshBuilder)
{
    meshBuilder.WithIndexType(IndexingType.Int16);
    meshBuilder.WithPrimitiveType(PrimitiveType.TriangleList);

    var position = meshBuilder.WithPosition<Vector3>();
    var color = meshBuilder.WithColor<Color>();

    meshBuilder.AddVertex();
    meshBuilder.SetElement(position, new Vector3(0, 0, 0));
    meshBuilder.SetElement(color, Color.Red);

    meshBuilder.AddVertex();
    meshBuilder.SetElement(position, new Vector3(1, 0, 0));
    meshBuilder.SetElement(color, Color.Green);

    meshBuilder.AddVertex();
    meshBuilder.SetElement(position, new Vector3(.5f, 1, 0));
    meshBuilder.SetElement(color, Color.Blue);

    meshBuilder.AddIndex(0);
    meshBuilder.AddIndex(2);
    meshBuilder.AddIndex(1);
}

void GiveMeAPlane(MeshBuilder meshBuilder)
{
    meshBuilder.WithIndexType(IndexingType.Int16);
    meshBuilder.WithPrimitiveType(PrimitiveType.TriangleList);

    var position = meshBuilder.WithPosition<Vector3>();
    var color = meshBuilder.WithColor<Color>();

    meshBuilder.AddVertex();
    meshBuilder.SetElement(position, new Vector3(0, 0, 0));
    meshBuilder.SetElement(color, Color.Red);

    meshBuilder.AddVertex();
    meshBuilder.SetElement(position, new Vector3(0, 1, 0));
    meshBuilder.SetElement(color, Color.Green);

    meshBuilder.AddVertex();
    meshBuilder.SetElement(position, new Vector3(1, 1, 0));
    meshBuilder.SetElement(color, Color.Blue);

    meshBuilder.AddVertex();
    meshBuilder.SetElement(position, new Vector3(1, 0, 0));
    meshBuilder.SetElement(color, Color.Yellow);

    meshBuilder.AddIndex(0);
    meshBuilder.AddIndex(1);
    meshBuilder.AddIndex(2);

    meshBuilder.AddIndex(0);
    meshBuilder.AddIndex(2);
    meshBuilder.AddIndex(3);
}

void GiveMeACircle(MeshBuilder meshBuilder, int segments)
{
    meshBuilder.WithIndexType(IndexingType.Int16);
    meshBuilder.WithPrimitiveType(PrimitiveType.TriangleList);

    var position = meshBuilder.WithPosition<Vector3>();
    var color = meshBuilder.WithColor<Color4>();

    for (var i = 0; i < segments; i++)
    {
        var x = (float)Math.Sin(Math.Tau / segments * i) / 2;
        var y = (float)Math.Cos(Math.Tau / segments * i) / 2;
        var hsl = new ColorHSV(360f / segments * i, 1, 1, 1).ToColor();

        meshBuilder.AddVertex();
        meshBuilder.SetElement(position, new Vector3(x + .5f, y + .5f, 0));
        meshBuilder.SetElement(color, hsl);
    }

    meshBuilder.AddVertex();
    meshBuilder.SetElement(position, new Vector3(.5f, .5f, 0));
    meshBuilder.SetElement(color, Color.Black.ToColor4());

    for (var i = 0; i < segments; i++)
    {
        meshBuilder.AddIndex(segments);
        meshBuilder.AddIndex(i);
        meshBuilder.AddIndex((i + 1) % segments);
    }
}

Entity AddMesh(GraphicsDevice graphicsDevice, Scene rootScene, Vector3 position, Action<MeshBuilder> build)
{
    using var meshBuilder = new MeshBuilder();
    build(meshBuilder);

    var entity = new Entity { Scene = rootScene, Transform = { Position = position } };
    var model = new Model
    {
        new MaterialInstance {
            Material = Material.New(graphicsDevice, new MaterialDescriptor {
                Attributes = new MaterialAttributes {
                    DiffuseModel = new MaterialDiffuseLambertModelFeature(),
                    Diffuse = new MaterialDiffuseMapFeature {
                        DiffuseMap = new ComputeVertexStreamColor()
                    },
                }
            })
        },
        new Mesh {
            Draw = meshBuilder.ToMeshDraw(graphicsDevice),
            MaterialIndex = 0
        }
    };
    entity.Add(new ModelComponent { Model = model });
    return entity;
}