using UnityEngine;
using UnityEngine.Rendering;
using UnityEngine.Experimental.Rendering;
using UnityEngine.Experimental.ScriptableRenderLoop;

// Very basic scriptable rendering loop example:
// - Use with BasicRenderLoopShader.shader (the loop expects "BasicPass" pass type to exist)
// - Supports up to 8 enabled lights in the scene (directional, point or spot)
// - Does the same physically based BRDF as the Standard shader
// - No shadows
// - This loop also does not setup lightmaps, light probes, reflection probes or light cookies

[ExecuteInEditMode]
public class BasicRenderLoop : ScriptableRenderLoop
{

#if UNITY_EDITOR
    [UnityEditor.MenuItem("Renderloop/CreateBasicRenderLoop")]
    static void CreateBasicRenderLoop()
    {
        var instance = ScriptableObject.CreateInstance<BasicRenderLoop>();
        UnityEditor.AssetDatabase.CreateAsset(instance, "Assets/basicrenderloop.asset");
    }
#endif

    private ShaderPassName shaderPassBasic;

    public void OnEnable()
    {
        Rebuild();
    }

    public override void Initialize()
    {
        shaderPassBasic = new ShaderPassName("BasicPass");
    }

    // Main entry point for our scriptable render loop
    public override void Render(Camera[] cameras, RenderLoop loop)
    {
        foreach (var camera in cameras)
        {
            // Culling
            CullingParameters cullingParams;
            if (!CullResults.GetCullingParameters (camera, out cullingParams))
                continue;
            CullResults cull = CullResults.Cull (ref cullingParams, loop);

            // Setup camera for rendering (sets render target, view/projection matrices and other
            // per-camera built-in shader variables).
            loop.SetupCameraProperties (camera);

            // clear depth buffer
            var cmd = new CommandBuffer();
            cmd.ClearRenderTarget(true, false, Color.black);
            loop.ExecuteCommandBuffer(cmd);
            cmd.Release();

            // Setup global lighting shader variables
            SetupLightShaderVariables (cull.visibleLights, loop);

            // Draw opaque objects using BasicPass shader pass
            var settings = new DrawRendererSettings (cull, camera, shaderPassBasic);
            settings.sorting.sortOptions = SortOptions.SortByMaterialThenMesh;
            settings.inputFilter.SetQueuesOpaque ();
            loop.DrawRenderers (ref settings);

            // Draw skybox
            loop.DrawSkybox (camera);

            // Draw transparent objects using BasicPass shader pass
            settings.sorting.sortOptions = SortOptions.BackToFront; // sort back to front
            settings.inputFilter.SetQueuesTransparent ();
            loop.DrawRenderers (ref settings);

            loop.Submit ();
        }
    }


    // Setup lighting variables for shader to use
    static void SetupLightShaderVariables (VisibleLight[] lights, RenderLoop loop)
    {
        // We only support up to 8 visible lights here. More complex approaches would
        // be doing some sort of per-object light setups, but here we go for simplest possible
        // approach.
        const int kMaxLights = 8;
        // Just take first 8 lights. Possible improvements: sort lights by intensity or distance
        // to the viewer, so that "most important" lights in the scene are picked, and not the 8
        // that happened to be first.
        int lightCount = Mathf.Min (lights.Length, kMaxLights);

        // Prepare light data
        Vector4[] lightColors = new Vector4[kMaxLights];
        Vector4[] lightPositions = new Vector4[kMaxLights];
        Vector4[] lightSpotDirections = new Vector4[kMaxLights];
        Vector4[] lightAtten = new Vector4[kMaxLights];
        for (var i = 0; i < lightCount; ++i)
        {
            VisibleLight light = lights[i];
            lightColors[i] = light.finalColor;
            if (light.lightType == LightType.Directional)
            {
                // light position for directional lights is: (-direction, 0)
                var dir = light.localToWorld.GetColumn (2);
                lightPositions[i] = new Vector4 (-dir.x, -dir.y, -dir.z, 0);
            }
            else
            {
                // light position for point/spot lights is: (position, 1)
                var pos = light.localToWorld.GetColumn (3);
                lightPositions[i] = new Vector4 (pos.x, pos.y, pos.z, 1);
            }
            // attenuation set in a way where distance attenuation can be computed:
            //	float lengthSq = dot(toLight, toLight);
            //	float atten = 1.0 / (1.0 + lengthSq * LightAtten[i].z);
            // and spot cone attenuation:
            //	float rho = max (0, dot(normalize(toLight), SpotDirection[i].xyz));
            //	float spotAtt = (rho - LightAtten[i].x) * LightAtten[i].y;
            //	spotAtt = saturate(spotAtt);
            // and the above works for all light types, i.e. spot light code works out
            // to correct math for point & directional lights as well.

            float rangeSq = light.range * light.range;

            float quadAtten = (light.lightType == LightType.Directional) ? 0.0f : 25.0f / rangeSq;

            // spot direction & attenuation
            if (light.lightType == LightType.Spot)
            {
                var dir = light.localToWorld.GetColumn (2);
                lightSpotDirections[i] = new Vector4 (-dir.x, -dir.y, -dir.z, 0);

                float radAngle = Mathf.Deg2Rad * light.spotAngle;
                float cosTheta = Mathf.Cos (radAngle * 0.25f);
                float cosPhi = Mathf.Cos (radAngle * 0.5f);
                float cosDiff = cosTheta - cosPhi;
                lightAtten[i] = new Vector4 (cosPhi, (cosDiff != 0.0f) ? 1.0f / cosDiff : 1.0f, quadAtten, rangeSq);
            }
            else
            {
                // non-spot light
                lightSpotDirections[i] = new Vector4 (0, 0, 1, 0);
                lightAtten[i] = new Vector4 (-1, 1, quadAtten, rangeSq);
            }
    	}

        // ambient lighting spherical harmonics values
        const int kSHCoefficients = 7;
        Vector4[] shConstants = new Vector4[kSHCoefficients];
        SphericalHarmonicsL2 ambientSH = RenderSettings.ambientProbe * RenderSettings.ambientIntensity;
        GetShaderConstantsFromNormalizedSH (ref ambientSH, shConstants);

        // setup global shader variables to contain all the data computed above
        CommandBuffer cmd = new CommandBuffer();
        cmd.SetGlobalVectorArray ("globalLightColor", lightColors);
        cmd.SetGlobalVectorArray ("globalLightPos", lightPositions);
        cmd.SetGlobalVectorArray ("globalLightSpotDir", lightSpotDirections);
        cmd.SetGlobalVectorArray ("globalLightAtten", lightAtten);
        cmd.SetGlobalVector ("globalLightCount", new Vector4 (lightCount, 0, 0, 0));
        cmd.SetGlobalVectorArray ("globalSH", shConstants);
        loop.ExecuteCommandBuffer (cmd);
        cmd.Dispose ();
    }


    // Prepare L2 spherical harmonics values for efficient evaluation in a shader
    static void GetShaderConstantsFromNormalizedSH (ref SphericalHarmonicsL2 ambientProbe, Vector4[] outCoefficients)
    {
        for (int channelIdx = 0; channelIdx < 3; ++channelIdx)
        {
            // Constant + Linear
            // In the shader we multiply the normal is not swizzled, so it's normal.xyz.
            // Swizzle the coefficients to be in { x, y, z, DC } order.
            outCoefficients[channelIdx].x = ambientProbe[channelIdx, 3];
            outCoefficients[channelIdx].y = ambientProbe[channelIdx, 1];
            outCoefficients[channelIdx].z = ambientProbe[channelIdx, 2];
            outCoefficients[channelIdx].w = ambientProbe[channelIdx, 0] - ambientProbe[channelIdx, 6];
            // Quadratic polynomials
            outCoefficients[channelIdx + 3].x = ambientProbe[channelIdx, 4];
            outCoefficients[channelIdx + 3].y = ambientProbe[channelIdx, 5];
            outCoefficients[channelIdx + 3].z = ambientProbe[channelIdx, 6] * 3.0f;
            outCoefficients[channelIdx + 3].w = ambientProbe[channelIdx, 7];
        }
        // Final quadratic polynomial
        outCoefficients[6].x = ambientProbe[0, 8];
        outCoefficients[6].y = ambientProbe[1, 8];
        outCoefficients[6].z = ambientProbe[2, 8];
        outCoefficients[6].w = 1.0f;
    }
}