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sketchpad-mouse.html
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<html>
<head>
<title>Sketchpad</title>
<script type="text/javascript">
// Variables for referencing the canvas and 2dcanvas context
var canvas, ctx;
var MOUSE_SIZE = 1;
// Variables to keep track of the mouse position and left-button status
var mouseX, mouseY, mouseDown = 0;
// Draws a dot at a specific position on the supplied canvas name
// Parameters are: A canvas context, the x position, the y position, the size of the dot
function drawDot(ctx, x, y, size) {
// Let's use black by setting RGB values to 0, and 255 alpha (completely opaque)
r = 0; g = 0; b = 0; a = 255;
// Select a fill style
ctx.fillStyle = "rgba(" + r + "," + g + "," + b + "," + (a / 255) + ")";
// Draw a filled circle
ctx.beginPath();
ctx.arc(x, y, size, 0, Math.PI * 2, true);
ctx.closePath();
ctx.fill();
}
// Clear the canvas context using the canvas width and height
function clearCanvas(canvas, ctx) {
ctx.clearRect(0, 0, canvas.width, canvas.height);
}
// Keep track of the mouse button being pressed and draw a dot at current location
function sketchpad_mouseDown() {
mouseDown = 1;
drawDot(ctx, mouseX, mouseY, MOUSE_SIZE);
}
// Keep track of the mouse button being released
function sketchpad_mouseUp() {
mouseDown = 0;
}
// Keep track of the mouse position and draw a dot if mouse button is currently pressed
function sketchpad_mouseMove(e) {
// Update the mouse co-ordinates when moved
getMousePos(e);
// Draw a dot if the mouse button is currently being pressed
if (mouseDown == 1) {
drawDot(ctx, mouseX, mouseY, MOUSE_SIZE);
}
}
// Get the current mouse position relative to the top-left of the canvas
function getMousePos(e) {
if (!e)
var e = event;
if (e.offsetX) {
mouseX = e.offsetX;
mouseY = e.offsetY;
}
else if (e.layerX) {
mouseX = e.layerX;
mouseY = e.layerY;
}
}
// Set-up the canvas and add our event handlers after the page has loaded
function init() {
// Get the specific canvas element from the HTML document
canvas = document.getElementById('sketchpad');
// If the browser supports the canvas tag, get the 2d drawing context for this canvas
if (canvas.getContext)
ctx = canvas.getContext('2d');
// Check that we have a valid context to draw on/with before adding event handlers
if (ctx) {
canvas.addEventListener('mousedown', sketchpad_mouseDown, false);
canvas.addEventListener('mousemove', sketchpad_mouseMove, false);
window.addEventListener('mouseup', sketchpad_mouseUp, false);
}
}
</script>
<style>
/* Some CSS styling */
#sketchpadapp {
/* Prevent nearby text being highlighted when accidentally dragging mouse outside confines of the canvas */
-webkit-touch-callout: none;
-webkit-user-select: none;
-khtml-user-select: none;
-moz-user-select: none;
-ms-user-select: none;
user-select: none;
}
.leftside {
float: left;
width: 220px;
height: 285px;
background-color: #def;
padding: 10px;
border-radius: 4px;
}
.rightside {
float: left;
margin-left: 10px;
}
#sketchpad {
float: left;
border: 2px solid #888;
border-radius: 4px;
position: relative;
/* Necessary for correct mouse co-ords in Firefox */
}
</style>
</head>
<body onload="init()">
<div id="sketchpadapp">
<div class="leftside">
Simple mouse-based HTML5 canvas sketchpad.<br/><br/> Draw something by holding down the mouse button or using single
clicks.
<br/><br/> On a touchscreen, tapping the area will register as a single mouse click.<br/><br/>
<input type="submit" value="Clear Sketchpad" onclick="clearCanvas(canvas,ctx);">
</div>
<div class="rightside">
<canvas id="sketchpad" height="300" width="400">
</canvas>
</div>
</div>
</body>
</html>