Drawing with mouse causes gaps between pixels

Question

I have been creating a drawing app as a test for WPF, and have been going well. The problem I\'ve run into is that if I draw the pixel under the mouse to a bitmap each time

Answer 1

I realize that you have already had your question answered, but wanted to post for the sake of anyone else who has this problem. I am one of those people.

I had a situation where my drawings looked exactly like the UPDATE section in the original question. The way I fixed this was by drawing overlapping lines by keeping track of not only the start and end points, but also a midpoint. When I draw, I draw using all three points, and then update start point -> midpoint, midpoint -> end point, end point -> new position relative to whatever you're drawing on. This made my lines look much, much better.

Hopefully this is helpful to someone who had the same issue as me.

Answer 2

If you want to draw a line, you shouldn't just change colors of one pixel at a time, but rather save position of the mouse in each MouseMove event handling method.

Then, you should draw a line between previous position (the one saved from the previous event occurrence) and draw a Line between those two points. This will make the line to be continuous. Information about drawing lines on WriteableBitmap can be found here: Drawing line using WPF WriteableBitmap.BackBuffer.

After drawing the line, don't forget to update the previous position saved to the current one :).

UPDATE

I've also found another solution.

Define XAML with Image you want to draw on:

<Window x:Class="SampleWPFApplication.MainWindow"
    xmlns="http://schemas.microsoft.com/winfx/2006/xaml/presentation"
    xmlns:x="http://schemas.microsoft.com/winfx/2006/xaml"
    Title="MainWindow" Height="500" Width="520" Loaded="Window_Loaded" PreviewMouseDown="Window_PreviewMouseDown">
<Grid x:Name="layoutRoot" Background="Transparent">
    <Image x:Name="image" />
</Grid>

And then, add code behind with the events handled:

//set width and height of your choice
RenderTargetBitmap bmp = null;
//...
private void Window_Loaded(object sender, RoutedEventArgs e)
    {
        //initialize RenderTargetBitmap object
        bmp = new RenderTargetBitmap((int)this.ActualWidth, (int)this.ActualHeight, 90, 90, PixelFormats.Default);

        //set initialized bmp as image's source
        image.Source = bmp;
    }

    /// <summary>
    /// Helper method drawing a line.
    /// </summary>
    /// <param name="p1">Start point of the line to draw.</param>
    /// <param name="p2">End point of the line to draw.</param>
    /// <param name="pen">Pen to use to draw the line.</param>
    /// <param name="thickness">Thickness of the line to draw.</param>
    private void DrawLine(Point p1, Point p2, Pen pen, double thickness)
    {
        DrawingVisual drawingVisual = new DrawingVisual();

        using (DrawingContext drawingContext = drawingVisual.RenderOpen())
        {
            //set properties of the Pen object to make the line more smooth
            pen.Thickness = thickness;
            pen.StartLineCap = PenLineCap.Round;
            pen.EndLineCap = PenLineCap.Round;

            //write your drawing code here
            drawingContext.DrawLine(pen, p1, p2);
        }
    }