/*******************************************************************************************
*
*   raylib [shaders] example - mesh instancing
*
*   Example complexity rating: [★★★★] 4/4
*
*   Example originally created with raylib 3.7, last time updated with raylib 4.2
*
*   Example contributed by seanpringle (@seanpringle) and reviewed by Max (@moliad) and Ramon Santamaria (@raysan5)
*
*   Example licensed under an unmodified zlib/libpng license, which is an OSI-certified,
*   BSD-like license that allows static linking with closed source software
*
*   Copyright (c) 2020-2025 seanpringle (@seanpringle), Max (@moliad) and Ramon Santamaria (@raysan5)
*
********************************************************************************************/

using Examples.Shared;

namespace Examples.Shaders;

public class MeshInstancing : IExample
{
    private const int screenWidth = 800;
    private const int screenHeight = 450;

#if BROWSER
    const int GlslVersion = 100;    // WebGL1 needs GLSL ES 100
#else
    private const int GlslVersion = 330;
#endif

    private const int MaxInstances = 10000;

    public string Name => "Shaders / Mesh Instancing";

    public string Title => "raylib [shaders] example - mesh instancing";

    private Camera3D camera;
    private Mesh cube;
    private Matrix4x4[] transforms;
    private Shader shader;
    private Material matInstances;
    private Material matDefault;

    public unsafe void Init()
    {
        // Define the camera to look into our 3d world
        camera = new();
        camera.Position = new Vector3(-125.0f, 125.0f, -125.0f);    // Camera position
        camera.Target = new Vector3(0.0f, 0.0f, 0.0f);              // Camera looking at point
        camera.Up = new Vector3(0.0f, 1.0f, 0.0f);                  // Camera up vector (rotation towards target)
        camera.FovY = 45.0f;                                        // Camera field-of-view Y
        camera.Projection = CameraProjection.Perspective;           // Camera projection type

        // Define mesh to be instanced
        cube = GenMeshCube(1.0f, 1.0f, 1.0f);

        // Define transforms to be uploaded to GPU for instances
        transforms = new Matrix4x4[MaxInstances];   // Pre-multiplied transformations passed to rlgl

        // Translate and rotate cubes randomly
        for (var i = 0; i < MaxInstances; i++)
        {
            var translation = Matrix4x4.CreateTranslation(
                GetRandomValue(-50, 50),
                GetRandomValue(-50, 50),
                GetRandomValue(-50, 50)
            );
            var axis = Vector3.Normalize(new Vector3(
                GetRandomValue(0, 360),
                GetRandomValue(0, 360),
                GetRandomValue(0, 360)
            ));
            var angle = GetRandomValue(0, 180) * DEG2RAD;
            var rotation = Matrix4x4.CreateFromAxisAngle(axis, angle);

            transforms[i] = Matrix4x4.Transpose(Matrix4x4.Multiply(rotation, translation));
        }

        // Load lighting shader
        shader = LoadShader(
            $"resources/shaders/glsl{GlslVersion}/lighting_instancing.vs",
            $"resources/shaders/glsl{GlslVersion}/lighting.fs"
        );
        // Get shader locations
        shader.Locs[(int)ShaderLocationIndex.MatrixMvp] = GetShaderLocation(shader, "mvp");
        shader.Locs[(int)ShaderLocationIndex.VectorView] = GetShaderLocation(shader, "viewPos");

        // Set shader value: ambient light level
        var ambientLoc = GetShaderLocation(shader, "ambient");
        Raylib.SetShaderValue(
            shader,
            ambientLoc,
            new float[] { 0.2f, 0.2f, 0.2f, 1.0f },
            ShaderUniformDataType.Vec4
        );

        // Create one light
        Rlights.CreateLight(
            0,
            LightType.Directorional,
            new Vector3(50.0f, 50.0f, 0.0f),
            Vector3.Zero,
            Color.White,
            shader
        );

        // NOTE: We are assigning the intancing shader to material.shader
        // to be used on mesh drawing with DrawMeshInstanced()
        matInstances = LoadMaterialDefault();
        matInstances.Shader = shader;
        matInstances.Maps[(int)MaterialMapIndex.Diffuse].Color = Color.Red;

        // Load default material (using raylib intenral default shader) for non-instanced mesh drawing
        // WARNING: Default shader enables vertex color attribute BUT GenMeshCube() does not generate vertex colors, so,
        // when drawing the color attribute is disabled and a default color value is provided as input for thevertex attribute
        matDefault = LoadMaterialDefault();
        matDefault.Maps[(int)MaterialMapIndex.Diffuse].Color = Color.Blue;
    }

    public unsafe void Update()
    {
        // Update
        //----------------------------------------------------------------------------------
        UpdateCamera(ref camera, CameraMode.Orbital);

        // Update the light shader with the camera view position
        float[] cameraPos = { camera.Position.X, camera.Position.Y, camera.Position.Z };
        Raylib.SetShaderValue(
            shader,
            shader.Locs[(int)ShaderLocationIndex.VectorView],
            cameraPos,
            ShaderUniformDataType.Vec3
        );
        //----------------------------------------------------------------------------------

        // Draw
        //----------------------------------------------------------------------------------
        BeginDrawing();

        ClearBackground(Color.RayWhite);

        BeginMode3D(camera);

        // Draw cube mesh with default material (BLUE)
        DrawMesh(cube, matDefault, Matrix4x4.Transpose(Matrix4x4.CreateTranslation(-10.0f, 0.0f, 0.0f)));

        // Draw meshes instanced using material containing instancing shader (RED + lighting),
        // transforms[] for the instances should be provided, they are dynamically
        // updated in GPU every frame, so we can animate the different mesh instances
        DrawMeshInstanced(cube, matInstances, transforms, MaxInstances);

        // Draw cube mesh with default material (BLUE)
        DrawMesh(cube, matDefault, Matrix4x4.Transpose(Matrix4x4.CreateTranslation(10.0f, 0.0f, 0.0f)));

        EndMode3D();

        DrawFPS(10, 10);

        EndDrawing();
        //----------------------------------------------------------------------------------
    }

    public void Unload()
    {
        // Detach shader so UnloadMaterial does not also unload it, then free everything.
        matInstances.Shader = new();
        UnloadMaterial(matInstances);
        UnloadMaterial(matDefault);
        UnloadMesh(cube);
        UnloadShader(shader);
    }

    public static int Main()
    {
        // Initialization
        //--------------------------------------------------------------------------------------
        InitWindow(screenWidth, screenHeight, "raylib [shaders] example - mesh instancing");

        SetTargetFPS(60);                   // Set our game to run at 60 frames-per-second
        //--------------------------------------------------------------------------------------

        var game = new MeshInstancing();
        game.Init();

        // Main game loop
        while (!WindowShouldClose())        // Detect window close button or ESC key
        {
            game.Update();
        }

        game.Unload();

        // De-Initialization
        //--------------------------------------------------------------------------------------
        CloseWindow();          // Close window and OpenGL context
        //--------------------------------------------------------------------------------------

        return 0;
    }
}