How to render ink data (HTML)
Learn how to render ink stroke segments as smooth Bézier curves.
Here, we show how to use the lineTo method to draw a stroke on the canvas in real time as the pen/stylus moves (see Quickstart: Capturing ink data) and the bezierCurveTo method to smooth and soften the stroke, when a user lifts the pen (or releases the left mouse button).
Updates for Windows 8.1: Windows 8.1 introduces a number of updates and improvements to the pointer input APIs. See API changes for Windows 8.1 for more info.
What you need to know
Technologies
Prerequisites
This topic builds on Quickstart: Capturing ink data.
We assume that you know how to create a basic Windows Store app using JavaScript that uses the Windows Library for JavaScript template.
- For instructions on creating your first Windows Store app, see Create your first Windows Store app using JavaScript.
- For info on using WinJS objects and controls, see Quickstart: Adding WinJS controls and styles.
Instructions
The renderAllStrokes function uses the inkManager to process each stroke segment through the bezierCurveTo method. The stroke is then redrawn using a smoother curve for each segment.
Important You can also use lineTo to render ink strokes. But lineTo uses the raw data provided by the input digitizer for rendering. With a frequency of more than 100 points per second, the amount of data that must be processed when using lineTo can degrade the performance of your app significantly. bezierCurveTo requires far fewer data points per stroke.
// Render all strokes using bezier curves instead of line segments.
function renderAllStrokes()
{
statusMessage.innerText += "Render strokes as bezier curves."
// Clear the drawing surface of existing strokes.
inkContext.clearRect(0, 0, inkCanvas.width, inkCanvas.height);
// Iterate through each stroke.
inkManager.getStrokes().forEach(
function (stroke)
{
inkContext.beginPath();
if (stroke.selected) {
inkContext.lineWidth = stroke.drawingAttributes.size.width * 2;
inkContext.strokeStyle = "green";
} else {
inkContext.lineWidth = stroke.drawingAttributes.size.width;
inkContext.strokeStyle = "black";
}
// Enumerate through each line segment of the stroke.
var first = true;
stroke.getRenderingSegments().forEach(
function (segment)
{
// Move to the starting screen location of the stroke.
if (first)
{
inkContext.moveTo(segment.position.x, segment.position.y);
first = false;
}
// Calculate the bezier curve for the segment.
else
{
inkContext.bezierCurveTo(segment.bezierControlPoint1.x,
segment.bezierControlPoint1.y,
segment.bezierControlPoint2.x,
segment.bezierControlPoint2.y,
segment.position.x, segment.position.y);
}
}
);
// Draw the stroke.
inkContext.stroke();
inkContext.closePath();
}
);
}
Complete example
//// THIS CODE AND INFORMATION IS PROVIDED "AS IS" WITHOUT WARRANTY OF
//// ANY KIND, EITHER EXPRESSED OR IMPLIED, INCLUDING BUT NOT LIMITED TO
//// THE IMPLIED WARRANTIES OF MERCHANTABILITY AND/OR FITNESS FOR A
//// PARTICULAR PURPOSE.
////
//// Copyright (c) Microsoft Corporation. All rights reserved
// Windows Store app that demonstrates the use of the Windows.UI.Input.Inking APIs.
// Ink functionality is documented at https://go.microsoft.com/fwlink/?LinkID=260649.
// User interaction functionality is documented at https://go.microsoft.com/fwlink/?LinkID=260650.
// Ink APIs are documented at https://go.microsoft.com/fwlink/?LinkID=260652.
// Pointer APIs are documented at https://go.microsoft.com/fwlink/?LinkID=260653.
(function ()
{
"use strict";
//
// Global variables
//
// UI object references.
var inkCanvas;
var inkContext;
var modeMessage;
var deviceMessage
var statusMessage;
// Create an ink manager.
// InkManager is documented at https://go.microsoft.com/fwlink/?LinkID=260648.
var inkManager = new Windows.UI.Input.Inking.InkManager();
// Initial pointer values.
var pointerId = -1;
var pointerDeviceType = null;
// Initial stroke property values.
var strokeColor;
var strokeWidth;
//
// End global variables
//
// Obtain reference to the specified element.
function get(elementId)
{
return document.getElementById(elementId);
}
function initialize()
{
// Set up the UI.
inkCanvas = get("inkCanvas");
inkContext = inkCanvas.getContext("2d");
inkContext.lineCap = "round";
inkContext.lineKJoin = "round";
inkCanvas.width = window.innerWidth - 10;
inkCanvas.height = window.innerHeight * 0.5;
deviceMessage = get("deviceMessage");
deviceMessage.innerText = "Undefined";
modeMessage = get("modeMessage");
modeMessage.innerText = inkManager.mode;
statusMessage = get("statusMessage");
statusMessage.innerText = "No pointer input detected."
// Set initial ink mode.
drawStrokes();
// Set default recognition language.
if (!setRecognizerByName("Microsoft English (US) Handwriting Recognizer")) {
statusMessage.innerText += "\nRecognition: Failed to find English (US) recognizer.";
}
else {
statusMessage.innerText += "\nRecognition: English (US) recognizer.";
}
// Set up the handlers for input processing.
inkCanvas.addEventListener("pointerdown", onPointerDown, false);
inkCanvas.addEventListener("pointermove", onPointerMove, false);
inkCanvas.addEventListener("pointerup", onPointerUp, false);
get("save").addEventListener("click", saveStrokes, false);
get("load").addEventListener("click", loadStrokes, false);
get("draw").addEventListener("click", drawStrokes, false);
get("select").addEventListener("click", selectStrokes, false);
get("selectall").addEventListener("click", selectAllStrokes, false);
get("erase").addEventListener("click", eraseStrokes, false);
get("eraseAll").addEventListener("click", eraseAllStrokes, false);
get("recognize").addEventListener("click", recognizeStrokes, false);
}
document.addEventListener("DOMContentLoaded", initialize, false);
function getPointerDeviceType(pId)
{
var pointerDeviceType;
var pointerPoint = Windows.UI.Input.PointerPoint.getCurrentPoint(pId);
switch (pointerPoint.pointerDevice.pointerDeviceType)
{
case Windows.Devices.Input.PointerDeviceType.touch:
pointerDeviceType = "Touch";
break;
case Windows.Devices.Input.PointerDeviceType.pen:
pointerDeviceType = "Pen";
break;
case Windows.Devices.Input.PointerDeviceType.mouse:
pointerDeviceType = "Mouse";
break;
default:
pointerDeviceType = "Undefined";
}
deviceMessage.innerText = pointerDeviceType;
return pointerDeviceType;
}
// Occurs when the pointer (touch, pen, mouse) is detected by the canvas.
// Each stroke begins with onPointerDown.
function onPointerDown(evt)
{
// Get the device type for the pointer input.
pointerDeviceType = getPointerDeviceType(evt.pointerId);
// Process pen and mouse (with left button) only. Reserve touch for manipulations.
if ((pointerDeviceType === "Pen") || ((pointerDeviceType === "Mouse") && (evt.button === 0)))
{
statusMessage.innerText = pointerDeviceType + " pointer down: Start stroke. "
// Process one pointer at a time.
if (pointerId === -1)
{
var current = evt.currentPoint;
// Start drawing the stroke.
inkContext.beginPath();
inkContext.lineWidth = strokeWidth;
inkContext.strokeStyle = strokeColor;
inkContext.moveTo(current.position.x, current.position.y);
// Add current pointer to the ink manager (begin stroke).
inkManager.processPointerDown(current);
// The pointer id is used to restrict input processing to the current stroke.
pointerId = evt.pointerId;
}
}
else
{
// Process touch input.
}
}
// Mouse: Occurs when the pointer moves.
// Pen/Touch: Occurs at a steady rate (approx. 100 messages/second) whether the pointer moves or not.
function onPointerMove(evt)
{
// Process pen and mouse (with left button) only. Reserve touch for manipulations.
if ((pointerDeviceType === "Pen") || ((pointerDeviceType === "Mouse") && (evt.button === -1)))
{
statusMessage.innerText = pointerDeviceType + " pointer move: Draw stroke as lines. "
// The pointer Id is used to restrict input processing to the current stroke.
// pointerId is updated in onPointerDown().
if (evt.pointerId === pointerId)
{
var current = evt.currentPoint;
// Draw stroke in real time.
inkContext.lineTo(current.rawPosition.x, current.rawPosition.y);
inkContext.stroke();
// Add current pointer to the ink manager (update stroke).
inkManager.processPointerUpdate(current);
}
}
else
{
// Process touch input.
}
}
// Occurs when the pointer (touch, pen, mouse) is lifted from the canvas.
// Each stroke ends with onPointerUp.
function onPointerUp(evt)
{
// Process pen and mouse (with left button) only. Reserve touch for manipulations.
if ((pointerDeviceType === "Pen") || ((pointerDeviceType === "Mouse") && (evt.button === 0)))
{
statusMessage.innerText = pointerDeviceType + " pointer up: Finish stroke. "
if (evt.pointerId === pointerId) {
// Add current pointer to the ink manager (end stroke).
inkManager.processPointerUp(evt.currentPoint);
// End live drawing.
inkContext.closePath();
// Render strokes using bezier curves.
renderAllStrokes();
// Reset pointer Id.
pointerId = -1;
}
}
else
{
// Process touch input.
}
}
// Render all strokes using bezier curves instead of line segments.
function renderAllStrokes()
{
statusMessage.innerText += "Render strokes as bezier curves."
// Clear the drawing surface of existing strokes.
inkContext.clearRect(0, 0, inkCanvas.width, inkCanvas.height);
// Iterate through each stroke.
inkManager.getStrokes().forEach(
function (stroke)
{
inkContext.beginPath();
if (stroke.selected) {
inkContext.lineWidth = stroke.drawingAttributes.size.width * 2;
inkContext.strokeStyle = "green";
} else {
inkContext.lineWidth = stroke.drawingAttributes.size.width;
inkContext.strokeStyle = "black";
}
// Enumerate through each line segment of the stroke.
var first = true;
stroke.getRenderingSegments().forEach(
function (segment)
{
// Move to the starting screen location of the stroke.
if (first)
{
inkContext.moveTo(segment.position.x, segment.position.y);
first = false;
}
// Calculate the bezier curve for the segment.
else
{
inkContext.bezierCurveTo(segment.bezierControlPoint1.x,
segment.bezierControlPoint1.y,
segment.bezierControlPoint2.x,
segment.bezierControlPoint2.y,
segment.position.x, segment.position.y);
}
}
);
// Draw the stroke.
inkContext.stroke();
inkContext.closePath();
}
);
}
// Set up draw mode.
function drawStrokes() {
inkManager.mode = Windows.UI.Input.Inking.InkManipulationMode.inking;
strokeColor = "black";
strokeWidth = 2;
modeMessage.innerText = inkManager.mode;
}
// Set up selection mode.
function selectStrokes() {
inkManager.mode = Windows.UI.Input.Inking.InkManipulationMode.selecting;
strokeColor = "red";
strokeWidth = 1;
modeMessage.innerText = inkManager.mode;
}
// Set up erase mode.
function eraseStrokes() {
inkManager.mode = Windows.UI.Input.Inking.InkManipulationMode.erasing;
strokeColor = "gold";
strokeWidth = 1;
modeMessage.innerText = inkManager.mode;
}
// Select all strokes handler.
function selectAllStrokes() {
inkManager.mode = Windows.UI.Input.Inking.InkManipulationMode.selecting;
strokeColor = "red";
strokeWidth = 1;
modeMessage.innerText = "Select all strokes.";
// Iterate through each stroke.
inkManager.getStrokes().forEach(
function (stroke) {
stroke.selected = 1;
}
);
renderAllStrokes();
}
// Select all strokes handler.
function eraseAllStrokes() {
inkManager.mode = Windows.UI.Input.Inking.InkManipulationMode.inking;
strokeColor = "black";
strokeWidth = 2;
modeMessage.innerText = "Erase all strokes.";
// Iterate through each stroke.
inkManager.getStrokes().forEach(
function (stroke) {
stroke.selected = 1;
}
);
inkManager.deleteSelected();
renderAllStrokes();
}
// Save all strokes owned by inkManager.
function saveStrokes()
{
// Ensure that strokes exist before calling saveAsync.
if (inkManager.getStrokes().size > 0)
{
// Set up the file save screen.
var savePicker = Windows.Storage.Pickers.FileSavePicker();
savePicker.suggestedStartLocation = Windows.Storage.Pickers.PickerLocationId.picturesLibrary;
savePicker.fileTypeChoices.insert("GIF with embedded ISF", [".gif"]);
savePicker.defaultFileExtension = ".gif";
// Set up the stream.
var saveStream = null;
// Asynchronously save the ink data to the stream.
savePicker.pickSaveFileAsync().done(
function (file)
{
if (null !== file)
{
file.openAsync(Windows.Storage.FileAccessMode.readWrite).then(
function (stream)
{
saveStream = stream;
return inkManager.saveAsync(saveStream);
}
).then(
function ()
{
return saveStream.flushAsync();
},
function (e) {
// Override the standard saveAsync error with our own.
throw new Error("saveAsync");
}
).done(
function ()
{
statusMessage.innerText = "Strokes saved as GIF with embedded ISF (.gif).";
saveStream.close();
},
function (e) {
statusMessage.innerText = "Save: " + e.toString();
// Close the stream if open.
if (saveStream) {
saveStream.close();
}
}
);
}
}
);
}
else
{
statusMessage.innerText = "No strokes to save.";
}
}
// Load strokes into an inkManager.
function loadStrokes()
{
// Set up the file open screen.
var openPicker = Windows.Storage.Pickers.FileOpenPicker();
openPicker.suggestedStartLocation = Windows.Storage.Pickers.PickerLocationId.picturesLibrary;
openPicker.fileTypeFilter.replaceAll([".gif"]);
// Set up the stream.
var loadStream = null;
// Asynchronously load the ink data from the stream.
openPicker.pickSingleFileAsync().done(
function (file)
{
if (null != file)
{
file.openAsync(Windows.Storage.FileAccessMode.read).then(
function (stream) {
loadStream = stream;
return inkManager.loadAsync(loadStream);
}).done(
function()
{
var strokes = inkManager.getStrokes().length;
if (strokes === 0)
{
statusMessage.innerText = "No strokes in file.";
}
else
{
statusMessage.innerText = strokes + " strokes loaded.";
}
renderAllStrokes();
loadStream.close();
},
function (e)
{
statusMessage.innerText = "Load failed.";
if (loadStream)
{
// Close the stream if open.
loadStream.close();
}
});
}
});
}
/// <summary>
/// Finds a specific recognizer, and sets the inkManager's default to that recognizer.
/// Returns true if successful.
/// </summary>
/// <param name="recognizerName">The name of the handwriting recognizer.</param>
function setRecognizerByName(recognizerName) {
try {
// recognizers is a normal JavaScript array
var recognizers = inkManager.getRecognizers();
for (var i = 0, len = recognizers.length; i < len; i++) {
if (recognizerName === recognizers[i].name) {
inkManager.setDefaultRecognizer(recognizers[i]);
return true;
}
}
}
catch (e) {
displayError("setRecognizerByName: " + e.toString());
}
return false;
}
/// <summary>
/// Invoked when the "Handwriting recognition" button is pressed.
/// The ink manager processes all strokes through recognizeAsync, which returns
/// the number of words detected and a set of recognition results for each word.
/// </summary>
/// <param name="evt">The event object.</param>
function recognizeStrokes(evt) {
// Ensure ink strokes exist before calling recognizeAsync.
if (inkManager.getStrokes().length > 0) {
// recognizeAsync fails if other recognition tasks are in progress.
try {
// The ink manager is used to store the recognition results.
// recognizeAsync has 3 modes: all | selected | recent.
// For this example, we process all strokes.
// recognizeAsync is documented at https://go.microsoft.com/fwlink/?LinkID=265172.
inkManager.recognizeAsync(Windows.UI.Input.Inking.InkRecognitionTarget.all).done
(
// The recognitionResult object returned by recognizeAsync exposes the
// bounding rect, strokes, and text candidates for each word.
// In this example, we simply display the word count and recognition results.
function (results) {
// recognizeAsync does not automatically update existing recognition results in the ink manager.
// updateRecognitionResults is documented at https://go.microsoft.com/fwlink/?LinkID=265175.
inkManager.updateRecognitionResults(results);
var x = inkManager.getRecognizers();
// Display the number of words returned in results.
statusMessage.innerText = "Words recognized: " + results.length.toString();
// Iterate through each word and display the ranked list of possible matches.
for (var i = 0; i < results.length; i++) {
statusMessage.innerText += "\nWord" + (i+1).toString() + ":";
var alts = results[i].getTextCandidates();
for (var j = 0; j < alts.length; j++) {
statusMessage.innerText += " " + alts[j].toString();
}
}
},
function (e) {
displayError("InkManager::recognizeAsync: " + e.toString());
}
);
}
catch (e) {
displayError("recognize: " + e.toString());
}
}
else {
statusMessage.innerText = "No strokes to recognize.";
}
}
// Returns true if any strokes inside the ink manager are selected; false otherwise.
function anySelected() {
var strokes = inkManager.getStrokes();
var len = strokes.length;
for (var i = 0; i < len; i++) {
if (strokes[i].selected) {
return true;
}
}
return false;
}
})();
Related topics
Conceptual
Responding to pen and stylus input
Quickstart: Capturing ink data
Reference
Samples (DOM)
Input: DOM pointer event handling sample
Samples (Windows Store app APIs)