Stefan Wick's Weblog - Development with Silverlight, WPF and Tablet PC

Silverlight 3 Beta: Perspective 3D

swick — Wed, 18 Mar 2009 10:24:00 GMT

Silverlight 3 Beta has been released today. This release includes a number of exciting new features that I want to illustrate with a series of quick samples on my blog. (more info on Silverlight 3 Beta and how to get the bits and tools).

The first new feature I want to show is Perspective 3D transformation. We have added a powerful new property 'Projection' to UIElement that lets you rotate and move any element in your tree in 3D space! The usage is very simple, no complicated math required - just set the Projection property to a PlaneProjection in XAML or code and specify how you want to rotate or move your elements. You can then change these properties dynamically at runtime, either through code or animations.

<Grid >

<Grid.Projection>

</Grid.Projection>

</Grid>

(More info on Perspective 3D in Silverlight 3 Beta)

Below is a live example of this new feature in action. The source is attached to this post. Note that you need the Silverlight 3 Beta Tools for VS in order to build the project. To view the live sample on this page you just need the Silverlight 3 Beta runtime installed. In the sample I have two surfaces back-to-back to each other, simulating a postcard in 3D space. Use the sliders to rotate the postcard around x, y or z axis. To demonstrate that the projected visuals are actually live and also take input, I have ink-enabled then, so you can draw on either side of the postcard.

The below sample has been update for the Silverlight 3 RTW Runtime (download)

Custom Ink Rendering in Silverlight 2

swick — Tue, 02 Dec 2008 00:26:00 GMT

Drawing ink with the built-in stroke objects works great for handwriting and annotations. In some scenarios, however, you may want something more fancy that takes advantage of Silverlight's rich graphics capabilities.

Creating ink strokes with a customized appearance is fairly straight forward with Silverlight 2. You basically collect StylusPoints in mouse events as usual, but instead of adding them to stroke objects, you just draw your own geometries or shapes at the stylus/mouse location.

When collecting sample points during the MouseMove event, please be sure to call the StylusDevice.GetStylusPoints() method and process all points returned from that call. This will ensure that stylus users will get the full fidelity of input points, since their pointing device reports points more often than the MouseMove events fires. Also it is good practice to interpolate points between sample points, since they won't usually be equidistant.

I have a attached a sample project that demonstrates the concept end-to-end using Ellipse shapes with a LinearGradientBrush to give my ink strokes a custom look. Below is live version of the sample for you to play with.

Back-of-pen Erasing in Silverlight

swick — Tue, 02 Dec 2008 00:25:00 GMT

As addendum to my previous post Erasing Ink in Silverlight 2 I want to show how to enable back-of-pen erasing for users with a compatible stylus device (e.g. on a Tablet PC or with an external Graphics Tablet).

The key that enables this scenario is the StylusDevice.Inverted property. It reports during mouse events whether the front-of-pen (stylus) or back-of-pen (eraser) is being used. The app can then switch into inking or erasing mode automatically, according to this value.

Here is the code-behind you need to add for an InkPresenter to enable this scenario:

public partial class Page : UserControl

{

public Page()

{

InitializeComponent();

}

private void inkPresenter_MouseLeftButtonDown(object sender,
MouseButtonEventArgs e)

{

inkPresenter.CaptureMouse();

if (e.StylusDevice.Inverted == false)

{

// ink mode

newStroke =

new Stroke(e.StylusDevice.GetStylusPoints(inkPresenter));

inkPresenter.Strokes.Add(newStroke);

}

else

{

// erase mode

erasePoints = e.StylusDevice.GetStylusPoints(inkPresenter);

}

private void inkPresenter_MouseMove(object sender, MouseEventArgs e)

{

if (e.StylusDevice.Inverted == false)

{

// ink mode

if (newStroke != null)

{

newStroke.StylusPoints.Add(

e.StylusDevice.GetStylusPoints(inkPresenter));

}

else if (e.StylusDevice.Inverted == true)

{

// erase mode

if (erasePoints != null)

{

erasePoints.Add(
e.StylusDevice.GetStylusPoints(inkPresenter));

StrokeCollection hitStrokes =
inkPresenter.Strokes.HitTest(erasePoints);

foreach (Stroke hitStroke in hitStrokes)

{

inkPresenter.Strokes.Remove(hitStroke);

}

private void inkPresenter_MouseLeftButtonUp(object sender,
MouseButtonEventArgs e)

{

inkPresenter.ReleaseMouseCapture();

erasePoints = null;

newStroke = null;

}

private StylusPointCollection erasePoints = null;

private Stroke newStroke = null;

}

Erasing Ink in Silverlight 2

swick — Sun, 30 Nov 2008 18:09:00 GMT

Another frequently asked question around inking in Silverlight is about erasing Ink strokes after they have been collected or loaded. Unlike WPF or the Tablet SDK for COM & Winforms, Silverlight does not come with controls that have built-in eraser modes in the box. However, with a little bit of code-behind you can implement those modes and adjust them to your specific needs. The key APIs you will need for this are StrokeCollection.HitTest() and Stroke.HitTest(). Both APIs take a collection of StylusPoints as input and they return a value indicating whether or not the ink stroke(s) have been hit. Based on that you can then modify your collection accordingly to represent the result of the erase operation. Popular inking apps (e.g. Windows Journal) offer two different modes of erasing:

Erase By Stroke:
Implementing this mode is fairly straight forward. Just pass the stylus points collected along the eraser path into the HitTest() method of your collection of ink strokes and the API will tell you which strokes to remove from your collection.

Erase By Point:
This one takes a little more effort to get right. We start like above, but then we don't remove the hit strokes. Instead, we figure out which segment of the stroke was hit (by using the Stroke.HitTest() API) and then we split the stroke by removing that segment.

I have attached a sample that implements both modes. You can also check out a live version of the sample below. The simplistic implementation of "Erase By Point" in the sample leaves some areas of improvements for the reader (or for a future blog post). Most notably, the size the chunk erased in this mode is not very consistent as it depends on several factors (distance points, location of the hit point, thickness of the stroke, etc.). A good improvement would be to add some logic that ensures the eraser always cuts a consistent chunk out of the ink strokes.

Saving Ink to IsolatedStorage with Silverlight 2

swick — Sat, 01 Nov 2008 21:38:00 GMT

One of the questions I have seen quite a few times in the Silverlight.net forums is how to persists (and de-persists) ink in Silverlight 2. Unlike WPF, Silverlight does not support a binary persistence format (ISF), but you can write some code to save and load ink to and from XAML. To demonstrate how to do this in a real world example, I am using another very cool feature in Silverlight 2: IsolatedStorage

IsolatedStorage is a per application, per computer, per user storage that offers a powerful, easy to use way for your web applications to store data locally on the user's and retrieve it later when the user visits your sites again on the same computer. You can use it like a file system, or as in the case of this example, simply use it to store application settings in key/value pairs. Learn more about how to do the latter here.

The goal of my application is to store the ink as XAML in IsolatedStorage when the user navigates away from the site. Upon return, the app will retrieve the persisted data from the storage, depersist it and present the ink to the user. Here are the relevant pieces of code (full code project is attached to this post).

Serializing and de-serializing ink strokes using XAML:

public string InkXAML

{

get

{

// persists ink strokes to XAML

StringBuilder builder = new StringBuilder();

XmlWriter writer = XmlWriter.Create(builder);

writer.WriteStartElement("StrokeCollection",

"http://schemas.microsoft.com/winfx/2006/xaml/presentation");

foreach (Stroke stroke in _presenter.Strokes)

{

writer.WriteStartElement("Stroke");

writer.WriteStartElement("Stroke.DrawingAttributes");

writer.WriteStartElement("DrawingAttributes");

writer.WriteAttributeString("Width",

stroke.DrawingAttributes.Width.ToString(invCult));

writer.WriteAttributeString("Height",

stroke.DrawingAttributes.Height.ToString(invCult));

writer.WriteAttributeString("Color",

string.Format(invCult, "#{0:X2}{1:X2}{2:X2}{3:X2}",

stroke.DrawingAttributes.Color.A,

stroke.DrawingAttributes.Color.R,

stroke.DrawingAttributes.Color.G,

stroke.DrawingAttributes.Color.B));

writer.WriteAttributeString("OutlineColor",

string.Format(invCult, "#{0:X2}{1:X2}{2:X2}{3:X2}",

stroke.DrawingAttributes.OutlineColor.A,

stroke.DrawingAttributes.OutlineColor.R,

stroke.DrawingAttributes.OutlineColor.G,

stroke.DrawingAttributes.OutlineColor.B));

writer.WriteEndElement();

writer.WriteStartElement("Stroke.StylusPoints");

writer.WriteStartElement("StylusPointCollection");

foreach (StylusPoint sp in stroke.StylusPoints)

{

writer.WriteStartElement("StylusPoint");

writer.WriteAttributeString("X", sp.X.ToString(invCult));

writer.WriteAttributeString("Y", sp.Y.ToString(invCult));

writer.WriteEndElement();

}

writer.WriteEndElement();

}

writer.WriteEndElement();

writer.Flush();

return builder.ToString();

}

set

{

// depersist ink strokes from XAML

try

{

_presenter.Strokes = XamlReader.Load(value) as StrokeCollection;

}

catch (Exception exc) { Debug.WriteLine(exc.ToString()); }

}

Persisting data on Application exit:

void Application_Exit(object sender, EventArgs e)

{

IsolatedStorageSettings settings = IsolatedStorageSettings.ApplicationSettings;

string inkXAML = _inkCollector.InkXAML;

if (settings.Contains("Ink"))

{

settings["Ink"] = inkXAML;

}

else

{

settings.Add("Ink", inkXAML);

}

Loading data on Application startup:

public Page()

{

InitializeComponent();

_inkCollector = new InkCollector(inkNote);

IsolatedStorageSettings settings =

IsolatedStorageSettings.ApplicationSettings;

string inkXAML = "";

if (settings.Contains("Ink"))

{

inkXAML = settings["Ink"] as string;

_inkCollector.InkXAML = inkXAML;

}

If you have Silverlight 2 installed (who hasn't? :-)), you can try it out live below. Draw some ink, navigate away, close the browser, clear the cache, etc. Then return to my blog and see that your ink is back, due to the power of IsolatedStorage.

TabletPC Development Gotchas Part 7: Detecting the input device in Silverlight 2

swick — Sat, 01 Nov 2008 20:07:00 GMT

When writing an application that supports multiple input devices (mouse, stylus, touch) it is often neccessary to detect which type of device is sending the input events.Silverlight 1.0 offered a DeviceType property on the StylusInfo object that gets reported in every mouse event.

In the Silverlight 2 managed API, you will not find an equivelnt object that provides this information. We omitted it on purpose in this release, because adding this to the OM could not be done in a way that would make the Silverlight API a compatible subset of the WPF API. In future versions of both platforms we will provide a consistent way to get to this information.

Omitting this for now is acceptable since we do provide a workaround to get to this information, via the HTML DOM bridge. Here is how you do it (full source attached):

Expose a scriptable method from managed code to handle the DeviceType information:

public Page()

{

InitializeComponent();

HtmlPage.RegisterScriptableObject("page", this);

}

[ScriptableMember]

public void SetDeviceType(string deviceType)

{

_deviceType = deviceType;

switch (_deviceType)

{

case "Mouse":

// add specific code for mouse

break;

case "Stylus":

// add specific code for stylus

break;

case "Touch":

// add specific code for touch

break;

}

Hook up to the MouseLeftButtonDown event in JavaScript and pass the StylusInfo.DeviceType information to managed code when the event fires:

function onSilverlightLoad(sender, args) {

// attach a JavaScript MouseDown event handler

var inkPresenter = sender._element.content.findName("inkPresenter");

inkPresenter.addEventListener("mouseLeftButtonDown", onMouseDown);

}

function onMouseDown(sender, args) {

// get the device type info and pass

// the information to the managed code

var stylusInfo = args.getStylusInfo();

var plugin = sender.getHost();

plugin.content.page.SetDeviceType(stylusInfo.deviceType.toString());

}

</script>

Now, as a proud owner of a Toshiba M700, I can run the solution and collect ink from different devices and the app automatically changes the pen attributes as I switch between input devices. Here is a screenshot showing ink strokes collected with the three different devices available on my Tablet PC:

Silverlight 2 Released - Write On!

swick — Tue, 14 Oct 2008 08:45:00 GMT

Now that Silverlight 2 is released, I finally got around to updating my blog after a long time of silence. For those of you interested in handwriting and Tablet related technologies, I want to start out with a canonical example of a Silverlight 2 Inking application. There have been a couple of OM changes since Beta1 around ink and stylus in Silverlight, mostly in order to make the Silverlight API more consistent with the WPF Ink/Stylus APIs.

Just like in Silverlight 1.0, the key element to inking is the InkPresenter which is a Canvas-like element with the ability to render ink strokes. To bring it to live and actually enable ink collection (and eraser) funtionality you will need to write some code-behind that responds to the user's input. In my example I have encapsulated the required code into a re-usable 'InkCollector' class (in InkCollector.cs), so you can just instantiate and assign it to your InkPresenter in order to get started with inking in your own projects.

Here is my example - source code attached - try it out by using your mouse or stylus to write and erase ink:

Ink in Silverlight 2 (Beta 1)

swick — Tue, 25 Mar 2008 15:07:00 GMT

I am very excited to write my first blog post about Silverlight 2 today, the project I am currently working on. In early March 2008 we shipped a public Beta for Silverlight 2 that you can download (along with all the neccessary tools) from http://silverlight.net/.

Today I want to introduce you to using Ink in your Silverlight 2 application, using the new managed object model. This post has two versions of a basic inking sample attached - a C# version and a VB.NET version. Let's take a look at the XAML first. The relevant piece here is the InkPresenter element, which is our inking surface that will host the ink strokes collected by the user:

<InkPresenter x:Name="inkCtrl" Cursor="Stylus"

MouseLeftButtonDown="inkCtrl_MouseLeftButtonDown"

MouseMove="inkCtrl_MouseMove"

MouseLeftButtonUp="inkCtrl_MouseLeftButtonUp"/>

Now we need to add a little bit of code behind in the mouse event handlers in order to collect strokes from the user's input. Note that the 'GetStylusPoints()' calls actually obtain the high fidelity stylus input when using a stylus, so you get optimal, smooth ink on a Tablet PC - or with an external Tablet input device on your desktop.

public partial class Page : UserControl

{

public Page()

{

InitializeComponent();

}

private void inkCtrl_MouseLeftButtonDown(object sender,

MouseButtonEventArgs e)

{

// capture mouse and create a new stroke

inkCtrl.CaptureMouse();

newStroke = new Stroke();

inkCtrl.Strokes.Add(newStroke);

// set the desired drawing attributes here

newStroke.DrawingAttributes.Color = Colors.Blue;

newStroke.DrawingAttributes.OutlineColor = Colors.Yellow;

newStroke.DrawingAttributes.Width = 6d;

newStroke.DrawingAttributes.Height = 6d;

// add the stylus points

newStroke.StylusPoints.AddStylusPoints(e.GetStylusPoints(inkCtrl));

}

private void inkCtrl_MouseMove(object sender,

MouseEventArgs e)

{

if (newStroke != null)

{

// add the stylus points

newStroke.StylusPoints.AddStylusPoints(e.GetStylusPoints(inkCtrl));

}

private void inkCtrl_MouseLeftButtonUp(object sender,

MouseButtonEventArgs e)

{

if (newStroke != null)

{

// add the stylus points

newStroke.StylusPoints.AddStylusPoints(e.GetStylusPoints(inkCtrl));

}

// release mouse capture and we are done

inkCtrl.ReleaseMouseCapture();

newStroke = null;

}

private Stroke newStroke = null;

}

And here is the result at runtime, after collecting a couple of strokeson my Tablet PC:

For a more advanced sample app that uses ink to annotate pictures and has support for erasing ink, please visit the Silverlight 2 Beta1 Gallery and look for the 'Image Snipper' sample. You can also run it directly from the below IFrame (requires the Silverlight 2 Beta1 runtime to be installed on your computer):

<embedded sample removed, since Silverlight 2 Beta1 is no longer relevant>

Silverlight Ice Skaters - a Holiday Greetings eCard

swick — Tue, 18 Dec 2007 20:47:00 GMT

In the spirit of the holiday season, I have created a little eCard using the Silverlight v1.0 SDK. Use the buttons to add ice skaters and falling snow to the scene :-)

Have a wonderful Holiday and a happy New Year 2008!

P.S. I am using the Silverlight Streaming Service to host the eCard. If you like it, you can embed it on your site by using the following HTML:

The source code for the eCard is attached to this post.

TabletPC Development Gotchas Part 6: InkCanvas Element Selection/Move/Resize

swick — Tue, 18 Dec 2007 20:46:00 GMT

WPF's InkCanvas element provides a lot of built-in functionality for several common, ink-related tasks like stylus gesture recognition, point and stroke erase, as well as the selection, resizing and moving of ink strokes. The key to those features is the 'EditingMode' property - which is nicely demonstrated in the InkCanvas EditingModes SDK sample (btw, it also demonstrates an implementation of an Undo/Redo stack for ink operations).

One little known, yet very cool feature is not demonstrated in this sample, though: The selection, resizing and moving functioality (i.e. EditingMode="Select") can not only be applied to ink strokes, but also to child elements of the InkCanvas. This can be very handy if you want to build, for example, a note-taking application that can also host text, pictures and other content besides the handwritten ink. You can then use the 'Select" mode to let the user re-arrange and resize all their content.

The "gotcha" I wanted to point in this blog post is a limitation in this feature: Child elements in an InkCanvas may be positioned in a variety of different ways: for example you can position them by setting a "Margin" or by setting any combination of "Canvas.Left/Right/Top/Bottom" attached properties. InkCanvas's selection/moving/resizing feature, however, only works on elements that have absolute positioning set via "Canvas.Left/Top".

Let's look at the following example markup:

<Window x:Class="InkCanvasElementSelection.Window1"

xmlns="http://schemas.microsoft.com/winfx/2006/xaml/presentation"

xmlns:x="http://schemas.microsoft.com/winfx/2006/xaml"

Title="InkCanvasElementSelection"

ResizeMode="NoResize"

Height="450" Width="450">

<Window.Resources>

</Style>

</Window.Resources>

<Grid>

<InkCanvas Name="inkCanvas" EditingMode="Select"

Background="LightGoldenrodYellow"

SelectionChanging="OnSelectionChanging">

<Rectangle.RenderTransform>

</Rectangle.RenderTransform>

</Rectangle>

</InkCanvas>

</Grid>

</Window>

Note that the markup subscribes to the 'SelectionChanging' event on the InkCanvas. Let's leave the implementation of that event handler empty for now to demonstrate the limitation. Also note that the four rectangles use different ways to position themselves on the InkCanvas. Only the blue rectangle uses the "Canvas.Left/Top" attached properties for positioning.

Now you can use the lasso tool to select one or more elements, and then try to move and resize them. You will notice that it only works correctly for the blue rectangle (because that one has been positioned via "Canvas.Left/Top"). For the other rectangles you won't get the desired move or resize results.

Now what can I do if there are child elements that have not been positioned via "Canvas.Left/Top"? Here is a workaround to make this feature work even for those elements: In the 'SelectionChanging' event - which fires whenever you change what content is selected - you can walk the list of child elements and ensure they are positioned via "Canvas.Left/Top". Here is a piece you can add to the above sample to demonstrate this approach:

void OnSelectionChanging(object sender, InkCanvasSelectionChangingEventArgs e)

{

ReadOnlyCollection<UIElement> elements = e.GetSelectedElements();

foreach (UIElement element in elements)

{

// obtain actual location of element relative to InkCanvas

Point locationInInkCanvas = element.TranslatePoint(new Point(0, 0),

inkCanvas);

// set the location via Left/Top properties

element.SetValue(InkCanvas.LeftProperty, locationInInkCanvas.X);

element.SetValue(InkCanvas.TopProperty, locationInInkCanvas.Y);

// un-set right/bottom properties

element.SetValue(InkCanvas.RightProperty, double.NaN);

element.SetValue(InkCanvas.BottomProperty, double.NaN);

// re-translate any render transform

Matrix matRender = element.RenderTransform.Value;

matRender.Translate(-matRender.OffsetX, -matRender.OffsetY);

element.RenderTransform = new MatrixTransform(matRender);

// set margins to zero

if (element is FrameworkElement)

{

((FrameworkElement)element).Margin = new Thickness(0d);

}

Now if re-run the sample you will find all rectangles from the original markup can be selected, moved and resized as expected:

Full source code of this example is included in the attached Visual Studio project.

Snipping Pictures with Silverlight

swick — Tue, 18 Dec 2007 20:45:00 GMT

One of my favorite tools on the Tablet PC is the 'Snipping Tool'. I have been using it frequently since the early XP days (back then we shipped it seperately as a Power Toy). Now in Vista, it's part of the main OS and I find myself using it quite often event on my desktop PC.

When I was using the tool recently, I got this idea for a new Silverlight sample app: wouldn't it be cool to snip pieces from various images and put them together as a collage in Silverlight - and then annotate the result with text, drawings and/or handwriting?

Silverlight's imaging and ink APIs make this fairly easy. Here are my results of this effort using Silverlight v1.0 - the sample demonstrates these features:

Select an image from an animated collection of pictures
Snip a piece of the selected image (free-form, rectangle or entire picture) and arrange it on the canvas
Use 'Image Tools' to control zoom, rotation and opacity of individual snippets
Use 'Text Tools' to add/change text annotations
Use 'Ink Tools' to add/change drawings and handwritten annotations
Full screen and embedded mode

Couple of notes and caveats:

The pictures are currently hardcoded (appropriate for the holiday season :-) ), but you can easily change that in the attached source code to use your own pictures or to pull images from the web.
When you launch the app from this blog, it opens up in full screen mode (since this is the best mode to view and use it). You can press the 'Esc' key or use the 'Miscellaneous' menu to go back to embedded mode.
In full screen mode Silverlight disables keyboard input (for security reasons). So if you want to enter some text annotations, please switch to embedded mode.
The 'Create Bitmap' button doesn't do anything in this version. The idea is to invoke some server-side code here to generate a bitmap of your collage. If there is interest in the community, this might be a good topic for a seperate blog post. But then again: if you are on Windows Vista, you can just use the Snipping Tool in the OS, to grab your collage and save it as bitmap :-)

The sample's complete source code is attached to this post. A live version, hosted via Silverlight Streaming, is included below for you try out. Click the button to launch the app:

Ink Reflections - in Silverlight

swick — Sun, 02 Dec 2007 08:25:00 GMT

I have received several question from folks about my earlier post on Ink Reflections in WPF. People were curious how to accomplish the same or a similar effect in Silverlight, in the absence of the VisualBrush object.

Clearly, WPF's VisualBrush is the main object that enables scenarios like this and it definitely makes their implementation straightforward. However, in Silverlight you can also accomplish effects like this with little bit of extra coding.

First of all, Silverlight has an ImageBrush and a VideoBrush, so as long as the visul you want to mirror is an image or a video, you can apply the same technique as used in my WPF sample and you are done.

If you want to mirror a different type of visual, you will have to manage the mirror yourself, meaning you have to create a secondary, mirrored visual and update it whenever the original changes.

I have created a sample that demonstrates both techniques together. The yellow background with silver border is an image that gets mirrored using an ImageBrush. The ink you draw (and erase) gets mirrored programmatically using some JavaScript code-behind.

The sample's source code is attached. A live version, hosted via Silverlight Streaming, is included below for you try out.

Rendering ink and image to a bitmap using WPF

swick — Sun, 02 Dec 2007 08:21:00 GMT

To follow-up on my previous blog post and to complete the story about rendering ink onto pictures and saving the results as a bitmap file, I want to show how this is done in WPF.

In WPF all rendering uses the pipeline - pictures, videos, ink, text, all gets rendered via WPF's 'Media Integration Layer'. As a result, it's very easy and straightforward to combine rendering these different types, both on screen and on a bitmap.

I have attached a WPF sample app that demonstrates how to collect ink on top of an image and then save the combined visual to a bitmap file. In fact, I have used this sample to create the sample picture that is included in my previous post about doing this in Winforms. Here is a screenshot of the sample app (btw, the ink color picker is borrowed from the InkColorPicker SDK sample).

The key class to accomplish our job in WPF is the RenderTargetBitmap class. Here is the relevant code snippet from the sample app:

// render InkCanvas' visual tree to the RenderTargetBitmap

RenderTargetBitmap targetBitmap =

new RenderTargetBitmap((int)inkCanvas1.ActualWidth,

(int)inkCanvas1.ActualHeight,

96d, 96d,

PixelFormats.Default);

targetBitmap.Render(inkCanvas1);

// add the RenderTargetBitmap to a Bitmapencoder

BmpBitmapEncoder encoder = new BmpBitmapEncoder();

encoder.Frames.Add(BitmapFrame.Create(targetBitmap));

// save file to disk

FileStream fs = File.Open(fileName, FileMode.OpenOrCreate);

encoder.Save(fs);

Unlike the Winforms API, there is no behavioral difference between Windows Vista and Windows XP.

TabletPC Development Gotchas Part 5: Rendering ink and image to a bitmap using Winforms

swick — Sun, 02 Dec 2007 08:19:00 GMT

Annotating pictures with handwriting or drawings is a fun and useful scenario for digital ink. In many cases the application user wants to create a new image file with the ink annotation "burnt" into the picture, so they can use the result of their work in other contexts and with other applications (e.g. attach the annotated image to an e-mail or upload it to their personal web site or blog, like the image below).

So rendering ink on top of an image is a common scenario for TabletPC/Ink developers - and it should be real easy, right? Well, there is an important 'gotcha' you need to know about if you want to do this from Winforms. But let's start with native code first.

Using the COM Ink API in native code

If you are using the ActiveX version of InkPicture (or the COM InkOverlay component) then rendering its ink to a GDI bitmap is easy. Just get the hDC (handle to device context) of the bitmap and use the InkRenderer.Draw() method:

pInkRenderer->Draw(hDCtargetBitmap, pStrokesToRender);

Using the Winforms Ink API to target XP (Microsoft.Ink v1.7)

In managed Winforms code, the object that corresponds to the hDC is the System.Drawing.Graphics object. So the intuitive approach would be to get the Graphics object of the Winforms target bitmap and then use the Microsoft.Ink.Render.Draw() method to render the desired ink strokes on top of it. Something along the lines of this:

Graphics graphicsTarget = Graphics.FromImage(imageToSave);

inkPicture1.Renderer.Draw(graphicsTarget,

                            inkPicture1.Ink.Strokes);

imageToSave.Save(“InkAndImage.bmp”);

Unfortunately, the result of this operation does not look great: the quality of the ink on the bitmap is not the same as what you see on the screen. Especially if you set some advanced DrawingAttributes (like Transparency or RasterOperations) the resulting bitmap does resemble the image on the screen very well. What is the reason for this behavior? The short version is that the underlying Ink Renderer and the managed Winforms images use GDI in slightly different ways, so the rendering operation has to fall back to a lower quality mode.

Fortunately, there is a workaround: we can take both the Winforms image and our ink strokes and render them to a temporary device-independent-bitmap. Then we'll render the result of that to the actual target bitmap. In order to do this, however, we have to do some manged<->native code interop magic. All that magic is encapsulated in the DibGraphicsBuffer class (see highlighted line below). This helper class is included in the attached sample project. Here is the relevant code to apply the workaround using that helper class:

Graphics graphicsTarget = Graphics.FromImage(imageToSave);

Graphics graphicsSrc = inkPicture1.CreateGraphics();

DibGraphicsBuffer buffer = new DibGraphicsBuffer();

Graphics graphicsTemp = buffer.RequestBuffer(graphicsSrc,

                                               inkPicture1.Image.Width,

                                               inkPicture1.Image.Height);

graphicsTemp.DrawImage(inkPicture1.Image, new Point(0, 0));

inkPicture1.Renderer.Draw(graphicsTemp, inkPicture1.Ink.Strokes);

buffer.PaintBuffer(graphicsTarget, 0, 0);

Using the Winforms Ink API to target Vista (Microsoft.Ink v6.0)

In order to address the limitation of the XP API, the Vista version of Render.Draw() now has an additional overload that makes the above workaround obsolete (of course the workaround still works on Vista). You can now pass in a Bitmap object directly to the API, and your ink gets rendered onto the image in the highest quality with a one-liner:

inkPicture1.Renderer.Draw((Bitmap)imageToSave, inkPicture1.Ink.Strokes);

Attached Code projects:

I have attached two complete code projects to illustrate how to get the best results on both XP and Vista:

1) RenderInkOnBitmapXP - utilizes the DibGraphicsBuffer class to apply the workaround for Windows XP

2) RenderInkOnBitmapVista - uses the new overload to demonstrate the best practice on Windows Vista

Annotating Video with Ink using Silverlight

swick — Thu, 15 Nov 2007 16:44:00 GMT

Silverlight makes delivering video content in the browser very easy. Silverlight also has ink support built-in. So why not combine these two features to enable some great new scenarios?

I have put together a little sample using Silverlight v1.0 to record and play back ink annotations, synchronized with the video playback. Below is the key piece of XAML markup for this application. We are using an InkPresenter that hosts the MediaElement with the video and takes care of the ink renderering. Also note the empty storyboard here as this is the magic sauce for the synchronized ink playback.

<InkPresenter Name='inkPresenter' Canvas.Left='10' Canvas.Top='10'

MouseLeftButtonDown='onInkPresenterDown'

MouseMove='onInkPresenterMove'

MouseLeftButtonUp='onInkPresenterUp'>

<InkPresenter.Resources>

<Storyboard Duration="0:0:0" Completed="onStrokePlaybackTimerTick"

x:Name="strokePlaybackTimer" />

</InkPresenter.Resources>

<MediaElement Name='mediaElement' Source='bear.wmv'

Width='720' Height='480'

AutoPlay='False' MediaEnded='onMediaEnded'/>

</InkPresenter>

The relevant pieces in the JavaScript code behind the XAML (in file events.js), are the following functions:

ConvertInkToString(strokes) - a function to serialize the point data for the ink strokes into a string for persistence purposes
ConvertStringToInk(serializedStylusPoints) - the reverse function that returns a StrokeCollection for a serialized ink string
onStrokePlaybackTimerTick() - during playback this function is called on every frame; when it is time to play back a stroke, we do so point by point

The full source code is attached to this post. I have also uploaded the sample to the Silverlight Streaming service, so I can pull it directly into my blog here. To check it out, just click the button below to load the sample. Once the video is loaded, you can click the 'Playback' button to replay my pre-recorded ink annotation - or you can click 'Start Recording' to record your own annotations, and then play them back afterwards.