/*******************************************************************************************
*
*   raylib [shaders] example - Hybrid Rendering
*
*   Example originally created with raylib 4.2, last time updated with raylib 4.2
*
*   Example contributed by Buğra Alptekin Sarı (@BugraAlptekinSari) and reviewed by 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) 2022-2023 Buğra Alptekin Sarı (@BugraAlptekinSari)
*
********************************************************************************************/

using System;
using System.Numerics;
using static Raylib_cs.Raylib;

namespace Examples.Shaders;

public class HybridRender
{
    struct RayLocs
    {
        public int CamPos;
        public int CamDir;
        public int ScreenCenter;
    }

    const int GLSL_VERSION = 330;

    public static int Main()
    {
        // Initialization
        //--------------------------------------------------------------------------------------
        const int screenWidth = 800;
        const int screenHeight = 450;

        InitWindow(screenWidth, screenHeight, "raylib [shaders] example - hybrid render");

        // This shader calculates pixel depth and color using raymarch
        Shader shdrRaymarch = LoadShader(null, $"resources/shaders/glsl{GLSL_VERSION}/hybrid_raymarch.fs");

        // This Shader is a standard rasterization fragment shader with the addition of depth writing
        // You are required to write depth for all shaders if one shader does it
        Shader shdrRaster = LoadShader(null, $"resources/shaders/glsl{GLSL_VERSION}/hybrid_raster.fs");

        // Declare struct used to store camera locs
        RayLocs marchLocs = new();

        // Fill the struct with shader locs.
        marchLocs.CamPos = GetShaderLocation(shdrRaymarch, "camPos");
        marchLocs.CamDir = GetShaderLocation(shdrRaymarch, "camDir");
        marchLocs.ScreenCenter = GetShaderLocation(shdrRaymarch, "screenCenter");

        // Transfer screenCenter position to shader. Which is used to calculate ray direction.
        Vector2 screenCenter = new(screenWidth / 2, screenHeight / 2);
        SetShaderValue(
            shdrRaymarch,
            marchLocs.ScreenCenter,
            screenCenter,
            ShaderUniformDataType.SHADER_UNIFORM_VEC2
        );

        // Use customized function to create writable depth texture buffer
        RenderTexture2D target = LoadRenderTextureDepthTex(screenWidth, screenHeight);

        // Define the camera to look into our 3d world
        Camera3D camera;
        camera.Position = new Vector3(0.5f, 1.0f, 1.5f);
        camera.Target = new Vector3(0.0f, 0.5f, 0.0f);
        camera.Up = new Vector3(0.0f, 1.0f, 0.0f);
        camera.FovY = 45.0f;
        camera.Projection = CameraProjection.CAMERA_PERSPECTIVE;

        // Camera FOV is pre-calculated in the camera Distance.
        float camDist = 1.0f / (MathF.Tan(camera.FovY * 0.5f * Raylib.DEG2RAD));

        SetTargetFPS(60);
        //--------------------------------------------------------------------------------------

        // Main game loop
        while (!WindowShouldClose())
        {
            // Update
            //----------------------------------------------------------------------------------
            UpdateCamera(ref camera, CameraMode.CAMERA_ORBITAL);

            // Update Camera Postion in the ray march shader.
            SetShaderValue(
                shdrRaymarch,
                marchLocs.CamPos,
                camera.Position,
                ShaderUniformDataType.SHADER_UNIFORM_VEC3
            );

            // Update Camera Looking Vector. Vector length determines FOV.
            Vector3 camDir = Vector3.Normalize(camera.Target - camera.Position) * camDist;
            SetShaderValue(shdrRaymarch, marchLocs.CamDir, camDir, ShaderUniformDataType.SHADER_UNIFORM_VEC3);
            //----------------------------------------------------------------------------------

            // Draw
            //----------------------------------------------------------------------------------
            // Draw into our custom render texture (framebuffer)
            BeginTextureMode(target);
            ClearBackground(Color.WHITE);

            // Raymarch Scene
            // Manually enable Depth Test to handle multiple rendering methods.
            Rlgl.EnableDepthTest();
            BeginShaderMode(shdrRaymarch);
            DrawRectangleRec(new Rectangle(0, 0, screenWidth, screenHeight), Color.WHITE);
            EndShaderMode();

            // Rasterize Scene
            BeginMode3D(camera);
            BeginShaderMode(shdrRaster);
            DrawCubeWiresV(new Vector3(0.0f, 0.5f, 1.0f), new Vector3(1.0f, 1.0f, 1.0f), Color.RED);
            DrawCubeV(new Vector3(0.0f, 0.5f, 1.0f), new Vector3(1.0f, 1.0f, 1.0f), Color.PURPLE);
            DrawCubeWiresV(new Vector3(0.0f, 0.5f, -1.0f), new Vector3(1.0f, 1.0f, 1.0f), Color.DARKGREEN);
            DrawCubeV(new Vector3(0.0f, 0.5f, -1.0f), new Vector3(1.0f, 1.0f, 1.0f), Color.YELLOW);
            DrawGrid(10, 1.0f);
            EndShaderMode();
            EndMode3D();

            EndTextureMode();

            // Draw custom render texture
            BeginDrawing();
            ClearBackground(Color.RAYWHITE);

            DrawTextureRec(
                target.Texture,
                new Rectangle(0, 0, screenWidth, -screenHeight),
                Vector2.Zero,
                Color.WHITE
            );
            DrawFPS(10, 10);

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

        // De-Initialization
        //--------------------------------------------------------------------------------------
        UnloadRenderTextureDepthTex(target);
        UnloadShader(shdrRaymarch);
        UnloadShader(shdrRaster);

        CloseWindow();
        //--------------------------------------------------------------------------------------

        return 0;
    }

    // Load custom render texture, create a writable depth texture buffer
    private static unsafe RenderTexture2D LoadRenderTextureDepthTex(int width, int height)
    {
        RenderTexture2D target = new();

        // Load an empty framebuffer
        target.Id = Rlgl.LoadFramebuffer(width, height);

        if (target.Id > 0)
        {
            Rlgl.EnableFramebuffer(target.Id);

            // Create color texture (default to RGBA)
            target.Texture.Id = Rlgl.LoadTexture(
                null,
                width,
                height,
                PixelFormat.PIXELFORMAT_UNCOMPRESSED_R8G8B8A8,
                1
            );
            target.Texture.Width = width;
            target.Texture.Height = height;
            target.Texture.Format = PixelFormat.PIXELFORMAT_UNCOMPRESSED_R8G8B8A8;
            target.Texture.Mipmaps = 1;

            // Create depth texture buffer (instead of raylib default renderbuffer)
            target.Depth.Id = Rlgl.LoadTextureDepth(width, height, false);
            target.Depth.Width = width;
            target.Depth.Height = height;
            target.Depth.Format = PixelFormat.PIXELFORMAT_COMPRESSED_PVRT_RGBA;
            target.Depth.Mipmaps = 1;

            // Attach color texture and depth texture to FBO
            Rlgl.FramebufferAttach(
                target.Id,
                target.Texture.Id,
                FramebufferAttachType.RL_ATTACHMENT_COLOR_CHANNEL0,
                FramebufferAttachTextureType.RL_ATTACHMENT_TEXTURE2D,
                0
            );
            Rlgl.FramebufferAttach(
                target.Id,
                target.Depth.Id,
                FramebufferAttachType.RL_ATTACHMENT_DEPTH,
                FramebufferAttachTextureType.RL_ATTACHMENT_TEXTURE2D,
                0
            );

            // Check if fbo is complete with attachments (valid)
            if (Rlgl.FramebufferComplete(target.Id))
            {
                TraceLog(TraceLogLevel.LOG_INFO, $"FBO: [ID {target.Id}] Framebuffer object created successfully");
            }

            Rlgl.DisableFramebuffer();
        }
        else
        {
            TraceLog(TraceLogLevel.LOG_WARNING, "FBO: Framebuffer object can not be created");
        }

        return target;
    }

    // Unload render texture from GPU memory (VRAM)
    private static void UnloadRenderTextureDepthTex(RenderTexture2D target)
    {
        if (target.Id > 0)
        {
            // Color texture attached to FBO is deleted
            Rlgl.UnloadTexture(target.Texture.Id);
            Rlgl.UnloadTexture(target.Depth.Id);

            // NOTE: Depth texture is automatically
            // queried and deleted before deleting framebuffer
            Rlgl.UnloadFramebuffer(target.Id);
        }
    }
}