using System;

namespace UnityEngine.Rendering.PostProcessing
{
    [Serializable]
    public sealed class VectorscopeMonitor : Monitor
    {
        public int size = 256;
        public float exposure = 0.12f;

        ComputeBuffer m_Data;
        int m_ThreadGroupSizeX;
        int m_ThreadGroupSizeY;
            
        internal override void OnEnable()
        {
            m_ThreadGroupSizeX = 16;
            m_ThreadGroupSizeY = RuntimeUtilities.isAndroidOpenGL ? 8 : 16;
        }

        internal override void OnDisable()
        {
            base.OnDisable();

            if (m_Data != null)
                m_Data.Release();

            m_Data = null;
        }

        internal override bool NeedsHalfRes()
        {
            return true;
        }

        internal override void Render(PostProcessRenderContext context)
        {
            CheckOutput(size, size);
            exposure = Mathf.Max(0f, exposure);

            int count = size * size;
            if (m_Data == null)
                m_Data = new ComputeBuffer(count, sizeof(uint));
            else if (m_Data.count != count)
            {
                m_Data.Release();
                m_Data = new ComputeBuffer(count, sizeof(uint));
            }

            var compute = context.resources.computeShaders.vectorscope;
            var cmd = context.command;
            cmd.BeginSample("Vectorscope");

            var parameters = new Vector4(
                context.width / 2,
                context.height / 2,
                size,
                RuntimeUtilities.isLinearColorSpace ? 1 : 0
            );

            // Clear the buffer on every frame as we use it to accumulate values on every frame
            int kernel = compute.FindKernel("KVectorscopeClear");
            cmd.SetComputeBufferParam(compute, kernel, "_VectorscopeBuffer", m_Data);
            cmd.SetComputeVectorParam(compute, "_Params", parameters);
            cmd.DispatchCompute(compute, kernel,
                Mathf.CeilToInt(size / (float)m_ThreadGroupSizeX),
                Mathf.CeilToInt(size / (float)m_ThreadGroupSizeY),
                1
            );

            // Gather all pixels and fill in our histogram
            kernel = compute.FindKernel("KVectorscopeGather");
            cmd.SetComputeBufferParam(compute, kernel, "_VectorscopeBuffer", m_Data);
            cmd.SetComputeTextureParam(compute, kernel, "_Source", ShaderIDs.HalfResFinalCopy);
            cmd.DispatchCompute(compute, kernel, 
                Mathf.CeilToInt(parameters.x / m_ThreadGroupSizeX),
                Mathf.CeilToInt(parameters.y / m_ThreadGroupSizeY),
                1
            );

            // Generate the histogram texture
            var sheet = context.propertySheets.Get(context.resources.shaders.vectorscope);
            sheet.properties.SetVector(ShaderIDs.Params, new Vector4(size, size, exposure, 0f));
            sheet.properties.SetBuffer(ShaderIDs.VectorscopeBuffer, m_Data);
            cmd.BlitFullscreenTriangle(BuiltinRenderTextureType.None, output, sheet, 0);

            cmd.EndSample("Vectorscope");
        }
    }
}