//
/**
 * Copyright (c) 2018 Razeware LLC
 *
 * Permission is hereby granted, free of charge, to any person obtaining a copy
 * of this software and associated documentation files (the "Software"), to deal
 * in the Software without restriction, including without limitation the rights
 * to use, copy, modify, merge, publish, distribute, sublicense, and/or sell
 * copies of the Software, and to permit persons to whom the Software is
 * furnished to do so, subject to the following conditions:
 *
 * The above copyright notice and this permission notice shall be included in
 * all copies or substantial portions of the Software.
 *
 * Notwithstanding the foregoing, you may not use, copy, modify, merge, publish,
 * distribute, sublicense, create a derivative work, and/or sell copies of the
 * Software in any work that is designed, intended, or marketed for pedagogical or
 * instructional purposes related to programming, coding, application development,
 * or information technology.  Permission for such use, copying, modification,
 * merger, publication, distribution, sublicensing, creation of derivative works,
 * or sale is expressly withheld.
 *
 * THE SOFTWARE IS PROVIDED "AS IS", WITHOUT WARRANTY OF ANY KIND, EXPRESS OR
 * IMPLIED, INCLUDING BUT NOT LIMITED TO THE WARRANTIES OF MERCHANTABILITY,
 * FITNESS FOR A PARTICULAR PURPOSE AND NONINFRINGEMENT. IN NO EVENT SHALL THE
 * AUTHORS OR COPYRIGHT HOLDERS BE LIABLE FOR ANY CLAIM, DAMAGES OR OTHER
 * LIABILITY, WHETHER IN AN ACTION OF CONTRACT, TORT OR OTHERWISE, ARISING FROM,
 * OUT OF OR IN CONNECTION WITH THE SOFTWARE OR THE USE OR OTHER DEALINGS IN
 * THE SOFTWARE.
 */

#include <metal_stdlib>
#include <simd/simd.h>
#import "ShaderTypes.h"

using namespace metal;

struct Vertex {
  float4 position [[position]];
  float2 uv;
};

constant float2 quadVertices[] = {
  float2(-1, -1),
  float2(-1,  1),
  float2( 1,  1),
  float2(-1, -1),
  float2( 1,  1),
  float2( 1, -1)
};

vertex Vertex vertexShader(unsigned short vid [[vertex_id]])
{
  float2 position = quadVertices[vid];
  Vertex out;
  out.position = float4(position, 0, 1);
  out.uv = position * 0.5 + 0.5;
  return out;
}

fragment float4 fragmentShader(Vertex in [[stage_in]],
                               texture2d<float> tex)
{
  constexpr sampler s(min_filter::nearest,
                      mag_filter::nearest,
                      mip_filter::none);
  float3 color = tex.sample(s, in.uv).xyz;
  return float4(color, 1.0);
}

kernel void accumulateKernel(constant Uniforms & uniforms,
                             texture2d<float> renderTex,
                             texture2d<float, access::read_write> t,
                             uint2 tid [[thread_position_in_grid]])
{
  if (tid.x < uniforms.width && tid.y < uniforms.height) {
    float3 color = renderTex.read(tid).xyz;
    if (uniforms.frameIndex > 0) {
      float3 prevColor = t.read(tid).xyz;
      prevColor *= uniforms.frameIndex;
      color += prevColor;
      color /= (uniforms.frameIndex + 1);
    }
    t.write(float4(color, 1.0), tid);
  }
}