How to draw on screen for Windows Metro Style Apps in C#?

Question

I simply want the user to be able to draw on the screen with some sort of pointer.

I already have the code working that captures the pointer's position, but I can't figure out how to place the pixels or shapes or whatever onto the screen.

I found this useful tutorial:
http://www.dotnetspeaks.com/DisplayArticle.aspx?ID=137

And I've been looking at the documentation here:
http://msdn.microsoft.com/en-us/library/windows/apps/hh465055(v=VS.85).aspx

No luck so far. =( The tutorial is for Windows Phone 7, so it's a little bit different. =\ Help, please? =)

And this is what I have so far.

The drawing part:

    private void Image_PointerPressed(object sender, PointerEventArgs e)
    {
        Debug.WriteLine("Image_PointerPressed");
        isTracing = true;
    }

    private void Image_PointerReleased(object sender, PointerEventArgs e)
    {
        Debug.WriteLine("Image_PointerReleased");
        isTracing = false;
    }

    private void Image_PointerMoved(object sender, PointerEventArgs e)
    {
        Debug.WriteLine("Image_PointerMoved");
        Debug.WriteLine(e.GetCurrentPoint(this).Position);
        if (isTracing)
        {
            Debug.WriteLine("isTracing");

            Point pos = e.GetCurrentPoint(this).Position;
            Color color = Colors.Green;
            Line line = new Line() { X1 = pos.X, X2 = pos.X + 1, Y1 = pos.Y, Y2 = pos.Y + 1 };
            line.Stroke = new SolidColorBrush(color);
            line.StrokeThickness = 15;
            //// So how do I draw this line onto the screen?? ////

        }

    }

For reference, stuff elsewhere in the code:

    using System;
    using System.Collections.Generic;
    using System.Diagnostics;
    using System.IO;
    using System.Linq;
    using System.Threading.Tasks;
    using Multimedia.FFmpeg;
    using Windows.Foundation;
    using Windows.Storage;
    using Windows.Storage.Pickers;
    using Windows.Storage.Streams;
    using Windows.UI.Xaml;
    using Windows.UI.Xaml.Controls;
    using Windows.UI.Xaml.Shapes;
    using Windows.UI.Xaml.Media;
    using Windows.UI.Xaml.Input;
    using Windows.UI.Input;

    bool isTracing = false;

Answer 1

This sample project has code to draw on screen for Win 8 Store apps in C#/XAML:

http://code.msdn.microsoft.com/windowsapps/Drawing-on-a-Canvas-with-33510ae6

Here is the relevant C# file:

using System; 
using System.Collections.Generic; 
using System.IO; 
using System.Linq; 
using Windows.Devices.Input; 
using Windows.Foundation; 
using Windows.Foundation.Collections; 
using Windows.UI; 
using Windows.UI.Input; 
using Windows.UI.Input.Inking; //we need to add this name space in order to have many functions  
using Windows.UI.Xaml; 
using Windows.UI.Xaml.Controls; 
using Windows.UI.Xaml.Controls.Primitives; 
using Windows.UI.Xaml.Data; 
using Windows.UI.Xaml.Input; 
using Windows.UI.Xaml.Media; 
using Windows.UI.Xaml.Navigation; 
using Windows.UI.Xaml.Shapes; 
// The Blank Page item template is documented at http://go.microsoft.com/fwlink/?LinkId=234238 

namespace DrawingOnCanvasWithInkPen 
{ 
/// <summary> 
/// An empty page that can be used on its own or navigated to within a Frame. 
/// </summary> 
public sealed partial class MainPage : Page 
{ 
    InkManager _inkKhaled = new Windows.UI.Input.Inking.InkManager(); 
    private uint _penID; 
    private uint _touchID; 
    private Point _previousContactPt; 
    private Point currentContactPt; 
    private double x1; 
    private double y1; 
    private double x2; 
    private double y2; 


    public MainPage() 
    { 
        this.InitializeComponent(); 

        MyCanvas.PointerPressed += new PointerEventHandler(MyCanvas_PointerPressed); 
        MyCanvas.PointerMoved += new PointerEventHandler(MyCanvas_PointerMoved); 
        MyCanvas.PointerReleased += new PointerEventHandler(MyCanvas_PointerReleased); 
        MyCanvas.PointerExited += new PointerEventHandler(MyCanvas_PointerReleased); 
    } 


    #region PointerEvents 
    private void MyCanvas_PointerReleased(object sender, PointerRoutedEventArgs e) 
    { 
        if (e.Pointer.PointerId == _penID) 
        { 
            Windows.UI.Input.PointerPoint pt = e.GetCurrentPoint(MyCanvas); 

            // Pass the pointer information to the InkManager.  
            _inkKhaled.ProcessPointerUp(pt); 
        } 

        else if (e.Pointer.PointerId == _touchID) 
        { 
            // Process touch input 
        } 

        _touchID = 0; 
        _penID = 0; 

        // Call an application-defined function to render the ink strokes. 


        e.Handled = true; 
    } 

    private void MyCanvas_PointerMoved(object sender, PointerRoutedEventArgs e) 
    { 
        if (e.Pointer.PointerId == _penID) 
        { 
            PointerPoint pt = e.GetCurrentPoint(MyCanvas); 

            // Render a red line on the canvas as the pointer moves.  
            // Distance() is an application-defined function that tests 
            // whether the pointer has moved far enough to justify  
            // drawing a new line. 
            currentContactPt = pt.Position; 
            x1 = _previousContactPt.X; 
            y1 = _previousContactPt.Y; 
            x2 = currentContactPt.X; 
            y2 = currentContactPt.Y; 

            if (Distance(x1, y1, x2, y2) > 2.0) // We need to developp this method now  
            { 
                Line line = new Line() 
                { 
                    X1 = x1, 
                    Y1 = y1, 
                    X2 = x2, 
                    Y2 = y2, 
                    StrokeThickness = 4.0, 
                    Stroke = new SolidColorBrush(Colors.Green) 
                }; 

                _previousContactPt = currentContactPt; 

                // Draw the line on the canvas by adding the Line object as 
                // a child of the Canvas object. 
                MyCanvas.Children.Add(line); 

                // Pass the pointer information to the InkManager. 
                _inkKhaled.ProcessPointerUpdate(pt); 
            } 
        } 

        else if (e.Pointer.PointerId == _touchID) 
        { 
            // Process touch input 
        } 

    } 

    private double Distance(double x1, double y1, double x2, double y2) 
    { 
        double d = 0; 
        d = Math.Sqrt(Math.Pow((x2 - x1), 2) + Math.Pow((y2 - y1), 2)); 
        return d; 
    } 

    private void MyCanvas_PointerPressed(object sender, PointerRoutedEventArgs e) 
    { 
        // Get information about the pointer location. 
        PointerPoint pt = e.GetCurrentPoint(MyCanvas); 
        _previousContactPt = pt.Position; 

        // Accept input only from a pen or mouse with the left button pressed.  
        PointerDeviceType pointerDevType = e.Pointer.PointerDeviceType; 
        if (pointerDevType == PointerDeviceType.Pen || 
                pointerDevType == PointerDeviceType.Mouse && 
                pt.Properties.IsLeftButtonPressed) 
        { 
            // Pass the pointer information to the InkManager. 
            _inkKhaled.ProcessPointerDown(pt); 
            _penID = pt.PointerId; 

            e.Handled = true; 
        } 

        else if (pointerDevType == PointerDeviceType.Touch) 
        { 
            // Process touch input 
        } 
    } 

    #endregion 

    /// <summary> 
    /// Invoked when this page is about to be displayed in a Frame. 
    /// </summary> 
    /// <param name="e">Event data that describes how this page was reached.  The Parameter 
    /// property is typically used to configure the page.</param> 
    protected override void OnNavigatedTo(NavigationEventArgs e) 
    { 
    } 
} 

}

and xaml file:

<Page 

x:Class="DrawingOnCanvasWithInkPen.MainPage" 
xmlns="http://schemas.microsoft.com/winfx/2006/xaml/presentation" 
xmlns:x="http://schemas.microsoft.com/winfx/2006/xaml" 
xmlns:local="using:DrawingOnCanvasWithInkPen" 
xmlns:d="http://schemas.microsoft.com/expression/blend/2008" 
xmlns:mc="http://schemas.openxmlformats.org/markup-compatibility/2006" 
mc:Ignorable="d"> 

<Grid Background="{StaticResource ApplicationPageBackgroundThemeBrush}"> 
    <Canvas Name="MyCanvas" Background="White" HorizontalAlignment="Left" Height="513" Margin="83,102,0,0" VerticalAlignment="Top" Width="1056"/> 

</Grid> 

In its current state, it only processes pen or mouse input -- but I also got it to work for touch with only slight modifications.

Answer 2

The main problem in your code is that you're not attaching, the line to any XAML element i suggest you to do it to a Canvas element, more less like this:

newCanvas.Children.Add(line);

An alternative is to use Modern Components Drawing Library, it works on WinRT, uses .NET Graphics class like calls and draw directly on a XAML Canvas, note that if you want to save the image as a bitmap, you may need to use also WritableBitmapEx, as XAML Canvas can't be rendered to Bitmaps.

Answer 3

Here is a great code sample on how to do this using XAML shapes.

http://www.codeproject.com/Articles/416878/Metro-Paint

Answer 4

Short form:

• Add Lines and Rectangles to a panel
• Manipulate a bitmap directly
• Use an HTML5 Canvas element in a JavaScript/HTML project
• Write the whole thing in C++/DirectX

There is no way in Metro/XAML to override an OnRender() method or the like. Your options are to add existing graphical elements (eg from the Shapes namespace) to a Canvas or other Panel, or to directly manipulate the pixels in a bitmap and push that bitmap into an Image element.

Metro/C# only has retained-mode graphics drawing, which means the only thing it will render is objects that have been added to the view hierarchy. What you're looking for is some kind of immediate-mode graphics drawing, eg

myCanvas.DrawLine( fromPoint, toPoint );

This can be done in a JavaScript/HTML project using HTML5's Canvas object. Which, sadly, is the way I'm leaning for such a project. It's unfortunate that Microsoft is not providing an immediate-mode element for XAML projects but that's the way it is. C++/DirectX is also an option for doing custom drawing but requires a substantial reworking of everything else that you're doing in the app.

Answer 5

You should add the Line to a UI element such as a Canvas.