//
/**
 * Copyright (c) 2019 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.
 */


import Metal

extension Renderer {
  static func buildBRDF() -> MTLTexture? {
    let size = 256
    guard let brdfFunction = Renderer.library?.makeFunction(name: "integrateBRDF"),
      let brdfPipelineState = try? Renderer.device.makeComputePipelineState(function: brdfFunction),
      let commandBuffer = Renderer.commandQueue.makeCommandBuffer(),
      let commandEncoder = commandBuffer.makeComputeCommandEncoder() else { return nil }
    
    let descriptor = MTLTextureDescriptor.texture2DDescriptor(pixelFormat:.rg16Float,
                                                              width: size,
                                                              height: size, mipmapped: false)
    descriptor.usage = [.shaderRead, .shaderWrite]
    let lut = Renderer.device.makeTexture(descriptor: descriptor)
    
    commandEncoder.setComputePipelineState(brdfPipelineState)
    commandEncoder.setTexture(lut, index: 0)
    let threadsPerThreadgroup = MTLSizeMake(16, 16, 1)
    let threadgroups = MTLSizeMake(size / threadsPerThreadgroup.width,
                                   size / threadsPerThreadgroup.height, 1)
    commandEncoder.dispatchThreadgroups(threadgroups,
                                        threadsPerThreadgroup: threadsPerThreadgroup)
    commandEncoder.endEncoding()
    commandBuffer.commit()
    return lut
  }

}