Gradient with opacity not working...

[equinox2k]

Prerequisites

• I have written a descriptive issue title
• I have verified that I am running the latest version of ImageSharp
• I have verified if the problem exist in both DEBUG and RELEASE mode
• I have searched open and closed issues to ensure it has not already been reported

Description

Gradient's with alpha not working as expected

Steps to Reproduce

I have created an example that shows gradient not working as expected.. it should do a iOS style gradient overlay, however produces a semi transparent overlay but of a single color where alpha doesnt change...

using SixLabors.ImageSharp;
using SixLabors.ImageSharp.PixelFormats;
using SixLabors.ImageSharp.Processing;
using SixLabors.Primitives;
using SixLabors.Shapes;

namespace EQL.ImageProcessors
{
    public static class GlossProcessor
    {
        public static IImageProcessingContext ApplyGloss(this IImageProcessingContext ctx)
        {
            Size size = ctx.GetCurrentSize();
            IPathCollection glossPath = BuildGloss(size.Width, size.Height);
            var graphicsOptions = new GraphicsOptions(true)
            {
                ColorBlendingMode = PixelColorBlendingMode.Normal,
                AlphaCompositionMode = PixelAlphaCompositionMode.SrcAtop
            };
            var linearGradientBrush = new LinearGradientBrush(new Point(0, 0), new Point(0, size.Height / 2), GradientRepetitionMode.Repeat, new ColorStop(0, Color.White.WithAlpha(0.5f)), new ColorStop(1, Color.White.WithAlpha(0.25f)));
            return ctx.Fill(graphicsOptions, linearGradientBrush, glossPath);
        }

        private static IPathCollection BuildGloss(int imageWidth, int imageHeight)
        {
            var pathBuilder = new PathBuilder();
            pathBuilder.AddLine(new PointF(0, 0), new PointF(imageWidth, 0));
            pathBuilder.AddLine(new PointF(imageWidth, 0), new PointF(imageWidth, imageHeight * 0.4f));
            pathBuilder.AddBezier(new PointF(imageWidth, imageHeight * 0.4f), new PointF(imageWidth / 2, imageHeight * 0.6f), new PointF(0, imageHeight * 0.4f));
            pathBuilder.CloseFigure();
            return new PathCollection(pathBuilder.Build());
        }
    }
}

can be called by loading a image and applying via...

image.Mutate(i => i.ApplyGloss());

System Configuration

macOS

• ImageSharp version:
  0.7beta

[equinox2k]

@jongleur1983

[jongleur1983]

@equinox2k not exactly sure how if I can reproduce it correctly. Could you provide reference output and actual (wrong) output for some sample please? e.g. just a opaque red image and how it should look like would be great.

[equinox2k]

@jongleur1983, Here is the expected result...

And actual...

[equinox2k]

Code used from above and actual image created using...

            using (var image = new Image<Rgba32>(1024, 1024))
            {
                image.Mutate(i => i.Fill(Color.Red));
                image.Mutate(i => i.ApplyGloss());
                image.Save("actual.png");
            }

[JimBobSquarePants]

Fixed in #1046