/*

 Copyright (C) 2017 Apple Inc. All Rights Reserved.

 See LICENSE.txt for this sample’s licensing information

 Abstract:

 The vertex and fragment shaders.

 */

#include <metal_stdlib>

#include <simd/simd.h>

using namespace metal;

/*

 Vertex input/output structure for passing results

 from a vertex shader to a fragment shader.

*/

struct VertexInOut

{

    float4 position [[position]];

    float4 color;

    float2 texCoord [[user(texturecoord)]];

};

// Vertex shader for a textured quad.

vertex VertexInOut passthroughVertexShader(uint vid [[ vertex_id ]],

                                           constant float4* position [[ buffer(0) ]],

                                           constant packed_float4* color [[ buffer(1) ]],

                                           constant packed_float2* pTexCoords [[ buffer(2) ]])

{

    VertexInOut outVertex;

    // Copy the vertex, texture and color coordinates.

    outVertex.position =  position[vid];

    outVertex.color    =  color[vid];

    outVertex.texCoord =  pTexCoords[vid];

    return outVertex;

};

vertex VertexInOut vertexShader_DiagonalWipe(uint vid [[ vertex_id ]],

                                            constant float4* position [[ buffer(0) ]],

                                            constant packed_float4* color [[ buffer(1) ]],

                                            constant packed_float2* pTexCoords [[ buffer(2) ]])

{

    VertexInOut outVertex;

    outVertex.position =  position[vid];

    outVertex.color    =  color[vid];

    /*

     Invert the y texture coordinate -- this is a simple modification to prevent the frame 

     from being flipped while using the same algorithm from the ObjC/OpenGL target 

     'quadVertexCoordinates' function (see APLDiagonalWipeRenderer.m) to compute the vertex 

     data for the foreground frame.

    */

    outVertex.texCoord = pTexCoords[vid];

    outVertex.texCoord.y = 1.0 - outVertex.texCoord.y;

    return outVertex;

}

// Fragment shader for a textured quad.

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

                                          texture2d<half> tex2D [[ texture(0) ]])

{

    constexpr sampler quad_sampler;

    // Sample the texture to get the surface color at this point.

    half4 color = tex2D.sample(quad_sampler, inFrag.texCoord);

    return color;

}