/*

 Copyright (C) 2015 Apple Inc. All Rights Reserved.

 See LICENSE.txt for this sample’s licensing information

 Abstract:

 Textured Terrain shader.

 */

#include <metal_graphics>

#include <metal_matrix>

#include <metal_geometric>

#include <metal_math>

#include <metal_texture>

#include <metal_common>

using namespace metal;

struct VertexInOut

{

    float4 m_Position [[position]];

    float3 m_TexCoord [[user(texturecoord)]];

};

vertex VertexInOut texturedTerrainVertex(constant packed_float3  *pPosition        [[ buffer(0) ]],

                                      constant packed_float3  *pTexCoords       [[ buffer(1) ]],

                                      constant float4x4       *pMVP             [[ buffer(2) ]],

                                      constant float4x4       *pTextureMatrix   [[ buffer(3) ]],

                                      uint                     vid              [[ vertex_id ]])

{

    VertexInOut outVertices;

    outVertices.m_Position = *pMVP * float4(pPosition[vid], 1.0f);

    outVertices.m_TexCoord = float3(*pTextureMatrix * float4(pTexCoords[vid], 1.0f));

    return outVertices;

}

fragment half4 texturedTerrainFragment(VertexInOut             inFrag    [[ stage_in ]],

                                    texture2d_array<half>   tex2D     [[ texture(0) ]])

{

    float2 texCoord = float2(inFrag.m_TexCoord.x , inFrag.m_TexCoord.y);

    float slice = floor(inFrag.m_TexCoord.z);

    constexpr sampler sampler(coord::normalized, address::repeat, filter::linear);

    half4 a = tex2D.sample(sampler, texCoord, slice);

    half4 b = tex2D.sample(sampler, texCoord, slice+1);

    half4 color = mix(a, b, half4(fract(inFrag.m_TexCoord.z)));

    return color;

}