[BUG] Horizontal lines disappear when zoomed in

[afcsoft]

Description

Horizontal lines disappear when zoomed in using Matrix. Stroke width is irrelevant. Anti-aliasing helps to some extent but problem still pursue.

Code

// Matrix code
        var zoom = (float)skiaRenderer.Viewport.SceneZ;
        var dpi = 1.5f;

        var drawMatrix = SKMatrix.CreateScale((float)zoom, -(float)zoom);

        var halfScaledWidth = (float)canvas.ActualWidth * 0.5f;
        var halfScaledHeight = (float)canvas.ActualHeight * 0.5f;

        var actualX = -(float)skiaRenderer.Viewport.SceneX * zoom + (halfScaledWidth * dpi);
        var actualY = (float)skiaRenderer.Viewport.SceneY * zoom + (halfScaledHeight * dpi);

        drawMatrix.TransX = actualX;
        drawMatrix.TransY = actualY;

        e.Surface.Canvas.SetMatrix(drawMatrix);      
// Line drawing code
_paint.Color.WithAlpha(255);
_paint.IsAntialias = true;
_paint.StrokeWidth = (float)(1.5 / _viewport.SceneZ);
_paint.StrokeCap = SKStrokeCap.Round;
_paint.IsStroke = true;
surface.Canvas.DrawLine((float)line.Object.Coor.Y, (float)line.Object.Coor.X, (float)line.Coord.Y, (float)line.Coord.X, _paint);

Expected Behavior

No response

Actual Behavior

No response

Version of SkiaSharp

2.88.3 (Current)

Last Known Good Version of SkiaSharp

Other (Please indicate in the description)

IDE / Editor

Visual Studio (Windows)

Platform / Operating System

All

Platform / Operating System Version

No response

Devices

No response

Relevant Screenshots

No response

Relevant Log Output

No response

Code of Conduct

• [X] I agree to follow this project's Code of Conduct

[angelofb]

I have the same problem

if you can use 1 pixel width stroke then you can set hairline mode with StrokeWidth = 0 https://learn.microsoft.com/en-us/dotnet/api/skiasharp.skpaint.strokewidth?view=skiasharp-2.88#remarks

[taublast]

Try Math.Round() actualX and actualY and let us know.

[mattleibow]

I think this will need a sample. It can just be a simple drawing of a line and "zooming" with a slider or something.

There may be things you can do with the hairline if the line gets too thin (like @angelofb says) or make sure your values are not in some weird decimal value (like @taublast says).

But, if you can capture the values when they disappear, then we can also see.

Also, try the 3.x releases and see if the new Skia engine has any bug fixes. However, this is more likely you have a 0.1px line at a 0.3px offset with a scale of 1.05% or something.

[dotnet-policy-service[bot]]

Hi @afcsoft. We have added the status/needs-repro label to this issue, which indicates that we require steps and sample code to reproduce the issue before we can take further action. Please try to create a minimal sample project/solution or code samples which reproduce the issue, ideally as a GitHub repo that we can clone.

This issue will be closed automatically in 7 days if we do not hear back from you by then - please feel free to re-open it if you come back to this issue after that time.

[dotnet-policy-service[bot]]

Hi @afcsoft. We have added the status/needs-info label to this issue, which indicates that we have an open question for you before we can take further action. This issue will be closed automatically in 7 days if we do not hear back from you by then - please feel free to re-open it if you come back to this issue after that time.