HeatMap drawn with rectangles shows white lines

[PJvG]

Steps to reproduce

1. Add a PlotView to a WPF view with a binding to a PlotModel in the view model:
   <oxy:PlotView Model="{Binding MyPlotModel}"/>

2. Instantiate a PlotModel as followed:

    private PlotModel myPlotModel;
   
    public MyViewModel()
    {
        myPlotModel = new PlotModel { Title = "My Plot Model" };
        myPlotModel.Axes.Add(new LinearColorAxis
        {
            Maximum = 100,
            Minimum = 0,
            Palette = OxyPalettes.Cool(100)
        });
   
        myPlotModel.Axes.Add(new LinearAxis()
        {
            Title = "Z",
            StartPosition = 1,
            EndPosition = 0,
            Position = AxisPosition.Left
        });
        myPlotModel.Axes.Add(new LinearAxis()
        {
            Title = "X",
            Position = AxisPosition.Bottom
        });
    }
   

I also have a bindable property named MyPlotModel.

3. Add data to my plot model with some method accepting plotModel and heatmapData as parameters:

        var heatMap = new HeatMapSeries
        {
            X0 = parentViewModel.MinX,
            X1 = parentViewModel.MaxX,
            Y0 = parentViewModel.MinZ,
            Y1 = parentViewModel.MaxZ,
            RenderMethod = HeatMapRenderMethod.Rectangles,
            Interpolate = false,
            Data = heatmapData
        };
   
       plotModel.Series.Add(heatMap);
       plotModel.InvalidatePlot(true);
   

Platform:
.NET version: 4.6.1
WPF application

Expected behaviour

I want to see a plot without these strange white lines running through it.

Actual behaviour

I see a plot with strange white lines running through it, as seen in the following example:

[VisualMelon]

Aye, this is a recognised issue that I think I volunteered to fix a while back (solved by using DrawRectangleAsPolygon instead of DrawRectangle) but among other things I seem always to anger the OxyPlot CI, so it never quite happened. Discussion from another thread

As a temporary workaround, can you use a different HeatMapRenderMethod?

[PJvG]

Hey @VisualMelon, it works! Thanks!

I have changed HeatMapRenderMethod.Rectangles to HeatMapRenderMethod.Bitmap.

[objorke]

I think we could add a new method in IRenderContext:

        ScreenPoint SnapToDevicePixel(ScreenPoint p)

and implement a default in RenderContextBase that does nothing:

        public ScreenPoint SnapToDevicePixel(ScreenPoint p)
        {
            return p;
        }

for WPF CanvasRenderContext it could be something like:

        public CanvasRenderContext(Canvas canvas)
        {
            this.canvas = canvas;
            var source = PresentationSource.FromVisual(this.canvas);
            this.transformToDevice = source.CompositionTarget.TransformToDevice;
            this.transformFromDevice = source.CompositionTarget.TransformFromDevice;
...        
        }
 
        public ScreenPoint SnapToDevicePixel(ScreenPoint p)
        {
            var pixel = this.transformToDevice.Transform(this.ToPoint(p));
            var adjusted = this.transformFromDevice.Transform(new Point(Math.Round(pixel.X), Math.Round(pixel.Y)));
            return adjusted.ToScreenPoint();
        }