//
//  Shaders.metal
//  Terrain2
//
//  Created by Eryn Wells on 11/3/18.
//  Copyright © 2018 Eryn Wells. All rights reserved.
//

// File for Metal kernel and shader functions

#include <metal_stdlib>
#include <simd/simd.h>

// Including header shared between this Metal shader code and Swift/C code executing Metal API commands
#import "ShaderTypes.h"

using namespace metal;

typedef struct
{
    float3 position [[attribute(VertexAttributePosition)]];
    float2 texCoord [[attribute(VertexAttributeTexcoord)]];
    uint2 gridCoord [[attribute(VertexAttributeGridCoord)]];
} Vertex;

typedef struct
{
    float4 position [[position]];
    float2 texCoord;
} ColorInOut;

vertex ColorInOut vertexShader(Vertex in [[stage_in]],
                               texture2d<float> heights [[texture(0)]],
                               constant Uniforms & uniforms [[buffer(BufferIndexUniforms)]])
{
    constexpr sampler s(coord::pixel, address::clamp_to_zero, filter::linear);

    ColorInOut out;

    // TODO: Concerned about this.
    uint2 gridCoord(in.texCoord.x * heights.get_width(), in.texCoord.y * heights.get_height());
    float4 height = heights.read(gridCoord).rrrr;

    float4 position(in.position.x, height.r, in.position.z, 1.0);
    out.position = uniforms.projectionMatrix * uniforms.modelViewMatrix * position;
    out.texCoord = in.texCoord;

    return out;
}

fragment float4 fragmentShader(ColorInOut in [[stage_in]],
                               constant Uniforms & uniforms [[ buffer(BufferIndexUniforms) ]],
                               texture2d<half> colorMap     [[ texture(TextureIndexColor) ]])
{
    constexpr sampler colorSampler(mip_filter::linear,
                                   mag_filter::linear,
                                   min_filter::linear);

    half4 colorSample   = colorMap.sample(colorSampler, in.texCoord.xy);

    return float4(colorSample);
}