//
//  TerrainAlgorithms.metal
//  Terrain2
//
//  Created by Eryn Wells on 11/4/18.
//  Copyright © 2018 Eryn Wells. All rights reserved.
//

#include <metal_stdlib>
#include <metal_types>
#include "ShaderTypes.h"
#include "Random.hh"

using namespace metal;

kernel void updateGeometryHeights(texture2d<float> texture [[texture(GeneratorTextureIndexIn)]],
                                  constant float2 *texCoords [[buffer(GeneratorBufferIndexTexCoords)]],
                                  constant Uniforms &uniforms [[buffer(GeneratorBufferIndexUniforms)]],
                                  device packed_float3 *vertexes [[buffer(GeneratorBufferIndexMeshPositions)]],
                                  uint2 tid [[thread_position_in_grid]])
{
    constexpr sampler s(coord::normalized, address::clamp_to_zero, filter::linear);

    const uint vIdx = tid.y * uniforms.terrainSegments.x + tid.x;

    // Get the height from the texture.
    float2 texCoord = texCoords[vIdx];
    float4 height = texture.sample(s, texCoord);

    // Update the vertex data.
    vertexes[vIdx].y = height.r;
}

kernel void updateGeometryNormals(constant packed_float3 *meshPositions [[buffer(GeneratorBufferIndexMeshPositions)]],
                                  constant packed_ushort3 *indexes [[buffer(GeneratorBufferIndexIndexes)]],
                                  device packed_float3 *faceNormals [[buffer(GeneratorBufferIndexFaceNormals)]],
                                  device packed_float3 *faceMidpoints [[buffer(GeneratorBufferIndexFaceMidpoints)]],
                                  uint tid [[thread_position_in_grid]])
{
    const ushort3 triangleIndex = indexes[tid];

    const float3 v1 = meshPositions[triangleIndex.x];
    const float3 v2 = meshPositions[triangleIndex.y];
    const float3 v3 = meshPositions[triangleIndex.z];

    float3 side1 = v1 - v2;
    float3 side2 = v1 - v3;
    float3 normal = normalize(cross(side1, side2));
    faceNormals[tid] = normal;
    faceMidpoints[tid] = (1.0 / 3.0) * (v1 + v2 + v3);
}

kernel void updateGeometryVertexNormals()
{
    
}

#pragma mark - ZeroGenerator

kernel void zeroKernel(texture2d<float, access::write> outTexture [[texture(GeneratorTextureIndexOut)]],
                       uint2 tid [[thread_position_in_grid]])
{
    outTexture.write(0, tid);
}