ImageContrastModifier.cs

using Hast.Layer;
using Hast.Synthesis.Attributes;
using Hast.Transformer.SimpleMemory;
using SixLabors.ImageSharp;
using SixLabors.ImageSharp.PixelFormats;
using System.Threading.Tasks;

namespace Hast.Samples.SampleAssembly;

/// <summary>
/// Algorithm for changing the contrast of an image. Also see <c>ImageContrastModifiermSampleRunner</c> on what to
/// configure to make this work.
/// </summary>
public class ImageContrastModifier
{
    private const ushort Multiplier = 1000;

    private const int ChangeContrastImageWidthIndex = 0;
    private const int ChangeContrastImageHeightIndex = 1;
    private const int ChangeContrastContrastValueIndex = 2;
    private const int ChangeContrastImageStartIndex = 3;
    private const int HeaderSize = ChangeContrastImageStartIndex;

    [Replaceable(nameof(ImageContrastModifier) + "." + nameof(MaxDegreeOfParallelism))]
    private static readonly int MaxDegreeOfParallelism = 25;

    /// <summary>
    /// Changes the contrast of an image.
    /// </summary>
    /// <param name="memory">The <see cref="SimpleMemory"/> object representing the accessible memory space.</param>
    public virtual void ChangeContrast(SimpleMemory memory)
    {
        var imageWidth = (ushort)memory.ReadUInt32(ChangeContrastImageWidthIndex);
        var imageHeight = (ushort)memory.ReadUInt32(ChangeContrastImageHeightIndex);
        int contrastValue = memory.ReadInt32(ChangeContrastContrastValueIndex);

        if (contrastValue > 100) contrastValue = 100;
        else if (contrastValue < -100) contrastValue = -100;

        contrastValue = (100 + (contrastValue * Multiplier)) / 100;

        var tasks = new Task<PixelProcessingTaskOutput>[MaxDegreeOfParallelism];

        // Since we only need to compute the loop condition's right side once, not on each loop execution, it's an
        // optimization to put it in a separate variable. This way it's indeed computed only once.
        var pixelCount = imageHeight * imageWidth;
        var stepCount = pixelCount / MaxDegreeOfParallelism;

        if (pixelCount % MaxDegreeOfParallelism != 0)
        {
            // This will take care of the rest of the pixels. This is wasteful as on the last step not all Tasks will
            // work on something but it's a way to keep the number of Tasks constant.
            stepCount += 1;
        }

        for (int i = 0; i < stepCount; i++)
        {
            for (int t = 0; t < MaxDegreeOfParallelism; t++)
            {
                var pixelBytes = memory.Read4Bytes((i * MaxDegreeOfParallelism) + t + ChangeContrastImageStartIndex);

                // Using an input class to also pass contrastValue because it's currently not supported to access
                // variables from the parent scope from inside Tasks (you need to explicitly pass in all inputs). Using
                // an output class to pass the pixel values back because returning an array from Tasks is not supported
                // at the time either.
                tasks[t] = Task.Factory.StartNew(
                    inputObject =>
                    {
                        var input = (PixelProcessingTaskInput)inputObject;

                        return new PixelProcessingTaskOutput
                        {
                            R = ChangePixelValue(input.PixelBytes[0], input.ContrastValue),
                            G = ChangePixelValue(input.PixelBytes[1], input.ContrastValue),
                            B = ChangePixelValue(input.PixelBytes[2], input.ContrastValue),
                        };
                    },
                    new PixelProcessingTaskInput { PixelBytes = pixelBytes, ContrastValue = contrastValue });
            }

            Task.WhenAll(tasks).Wait();

            for (int t = 0; t < MaxDegreeOfParallelism; t++)
            {
                // It's no problem that we write just 3 bytes to a 4-byte slot.
                memory.Write4Bytes(
                    (i * MaxDegreeOfParallelism) + t + ChangeContrastImageStartIndex,
                    new[] { tasks[t].Result.R, tasks[t].Result.G, tasks[t].Result.B });
            }
        }
    }

    /// <summary>
    /// Changes the contrast of an image. Same as <see cref="ChangeContrast"/>. Used for Hast.Communication.Tester to
    /// access this sample by a common method name just for testing. Internal so it doesn't bother otherwise.
    /// </summary>
    /// <param name="memory">The <see cref="SimpleMemory"/> object representing the accessible memory space.</param>
    internal virtual void Run(SimpleMemory memory) => ChangeContrast(memory);

    /// <summary>
    /// Makes the required changes on the selected pixel.
    /// </summary>
    /// <param name="pixel">The current pixel value.</param>
    /// <param name="contrastValue">The contrast difference value.</param>
    /// <returns>The pixel value after changing the contrast.</returns>
    private byte ChangePixelValue(byte pixel, int contrastValue)
    {
        var correctedPixel = pixel * Multiplier / 255;
        // While floats/doubles are not supported yet, you can still use them in constant expressions like the one
        // below. This is because these will be evaluated during transformation, thus only the result (500 in this
        // case) will end up on hardware.
        correctedPixel -= (int)(0.5 * Multiplier);
        correctedPixel *= contrastValue;
        correctedPixel /= Multiplier;
        correctedPixel += (int)(0.5 * Multiplier);
        correctedPixel *= 255;
        correctedPixel /= Multiplier;

        if (correctedPixel < 0) correctedPixel = 0;
        else if (correctedPixel > 255) correctedPixel = 255;

        return (byte)correctedPixel;
    }

    private sealed class PixelProcessingTaskInput
    {
        public byte[] PixelBytes { get; set; }
        public int ContrastValue { get; set; }
    }

    private sealed class PixelProcessingTaskOutput
    {
        public byte R { get; set; }
        public byte G { get; set; }
        public byte B { get; set; }
    }

    /// <summary>
    /// Changes the contrast of an image.
    /// </summary>
    /// <param name="image">The image that we modify.</param>
    /// <param name="contrast">The value of the intensity to calculate the new pixel values.</param>
    /// <returns>Returns an image with changed contrast values.</returns>
    public Image<Rgba32> ChangeImageContrast(
        Image<Rgba32> image,
        int contrast,
        IHastlayer hastlayer = null,
        IHardwareGenerationConfiguration configuration = null)
    {
        var memory = CreateSimpleMemory(
            image,
            contrast,
            hastlayer,
            configuration);
        ChangeContrast(memory);
        return CreateImage(memory, image);
    }

    /// <summary>
    /// Creates a <see cref="SimpleMemory"/> instance that stores the image.
    /// </summary>
    /// <param name="image">The image to process.</param>
    /// <param name="contrastValue">The contrast difference value.</param>
    /// <returns>The instance of the created <see cref="SimpleMemory"/>.</returns>
    private SimpleMemory CreateSimpleMemory(
        Image<Rgba32> image,
        int contrastValue,
        IHastlayer hastlayer = null,
        IHardwareGenerationConfiguration configuration = null)
    {
        var pixelCount = image.Width * image.Height;
        // Padding rounds up to MaxDegreeOfParallelism.
        var padding = (MaxDegreeOfParallelism - (pixelCount % MaxDegreeOfParallelism)) % MaxDegreeOfParallelism;
        var cellCount = HeaderSize + pixelCount + padding;
        var memory = hastlayer == null
            ? SimpleMemory.CreateSoftwareMemory(cellCount)
            : hastlayer.CreateMemory(configuration, cellCount);

        memory.WriteUInt32(ChangeContrastImageWidthIndex, (uint)image.Width);
        memory.WriteUInt32(ChangeContrastImageHeightIndex, (uint)image.Height);
        memory.WriteInt32(ChangeContrastContrastValueIndex, contrastValue);

        image.ProcessPixelRows(pixelAccessor =>
        {
            for (var y = 0; y < pixelAccessor.Height; y++)
            {
                var row = pixelAccessor.GetRowSpan(y);
                for (int x = 0; x < image.Width; x++)
                {
                    var pixel = row[x];

                    // This leaves 1 byte unused in each memory cell, but that would make the whole logic a lot more
                    // complicated, so good enough for a sample; if we'd want to optimize memory usage, that would be
                    // needed.
                    memory.Write4Bytes(
                        (y * image.Width) + x + ChangeContrastImageStartIndex,
                        new[] { pixel.R, pixel.G, pixel.B, pixel.A });
                }
            }
        });

        return memory;
    }

    /// <summary>
    /// Creates an image from a <see cref="SimpleMemory"/> instance.
    /// </summary>
    /// <param name="memory">The <see cref="SimpleMemory"/> instance.</param>
    /// <param name="image">The original image.</param>
    /// <returns>Returns the processed image.</returns>
    private Image<Rgba32> CreateImage(SimpleMemory memory, Image<Rgba32> image)
    {
        var newImage = image.Clone();

        newImage.ProcessPixelRows(pixelAccessor =>
        {
            for (int y = 0; y < newImage.Height; y++)
            {
                var row = pixelAccessor.GetRowSpan(y);
                for (int x = 0; x < newImage.Width; x++)
                {
                    var bytes = memory.Read4Bytes((y * newImage.Width) + x + ChangeContrastImageStartIndex);
                    row[x] = new Rgba32(bytes[0], bytes[1], bytes[2], 255);
                }
            }
        });

        return newImage;
    }
}