I am having trouble displaying pictures on my canvas, especially when using Chrome.
I have a method that is called to draw a portrait (name, img, borders), but context.drawImage() doesn't seem to be working in Chrome. Any solutions?
Portrait.prototype.draw = function (context, x, y, tX, tY) {
context.save();
context.translate( tX, tY );
context.fillStyle = 'blue';
context.strokeStyle = 'black';
context.strokeRect(x, y, 160, 200);
context.fillRect(x, y, 160, 200);
context.stroke();
// adding the image
context.beginPath();
var img = new Image();
var link = this.getImageUrl();
img.src = link;
//context.drawImage(img,x+5,y+5); //works mozzila
img.onload = function () { context.drawImage(img,x+5,y+5); }
// partial work chrome but on refresh displays e.g two different portrait images in turn in a random portrait (if multiple portraits on canvas)
// text box
context.beginPath();
context.fillStyle = '#ffffff';
context.fillRect(x+5,y + 165,150,30);
// text
context.beginPath();
context.fillStyle = 'black';
var n = this.getName();
context.font = "25px Aerial";
context.fillText(n,x+5,y+190); // should give the name
context.restore();
};
You're passing img.onload a function which will be executed asynchronously, meaning the other lines of code will proceed before it's done. Wrap the entire "draw" in your image.onload function.
Portrait.prototype.draw = function (context, x, y, tX, tY) {
var img = new Image();
var link = this.getImageUrl();
img.src = link;
img.onload = function () {
context.save();
context.translate( tX, tY );
context.fillStyle = 'blue';
context.strokeStyle = 'black';
context.strokeRect(x, y, 160, 200);
context.fillRect(x, y, 160, 200);
context.stroke();
context.drawImage(img,x+5,y+5);
//...
}
};
Related
I want to set an image instead of painting the ball
My code is the following
ballPainter = {
BALL_FILL_STYLE: 'rgb(255,0,50)',
BALL_STROKE_STYLE: 'rgb()',
paint: function (ball, context) {
var imageObj = new Image();
context.save();
context.shadowColor = undefined;
context.lineWidth = 2;
context.fillStyle = this.BALL_FILL_STYLE;
context.strokeStyle = this.BALL_STROKE_STYLE;
context.beginPath();
context.arc(ball.left, ball.top,
ball.radius, -1, Math.PI*2, false);
context.clip();
context.fill();
context.stroke();
context.restore();
}
},
You might want to check
http://www.w3schools.com/tags/canvas_drawimage.asp
I'm not sure if you can crop an image to a cricle though (maybe if the image has a transparant background)
*edit apperently you can HTML5 Canvas - Fill circle with image
What my task is, is to draw a house then use a loop (at the bottom) to fill the canvas with the houses instead of manually placing each one.
Well I'm trying to work how to make every other house's door green. I've been trying to hack away at code for awhile now but I cannot figure it out.
I know all my house pieces should be in functions and what not but that is a later task for the work I am doing! Here's my code:
//Check to see if the browser supports
//the addEventListener function
if(window.addEventListener)
{
window.addEventListener
(
'load', //this is the load event
onLoad, //this is the evemnt handler we going to write
false //useCapture boolen value
);
}
//the window load event handler
function onLoad()
{
var canvas;
var context;
//this function will intialise our variables
function initialise()
{
// Fune the canvas element using its id attribute.
canvas = document.getElementById('canvas');
//if it couldn't be found
if (!canvas)
{
//make a message bok appear with an error message
alert('Error: i cannot find this "canvas" of which you speak. Please re-evaluate your life choices.');
return;
}
//check if there is any getContext function
if(!canvas.getContext)
{
alert('Error no cavnas.getContext could be found');
return;
}
//get the 2D canvas context.
context = canvas.getContext('2d');
if(!context)
{
alert('Error failed to getCOntext');
return;
}
canvas.addEventListener("mousedown", getPosition, false);
}
// this is a little help tool for me as i'm awful at working out co-ordinates
function getPosition(e)
{
var x = e.x;
var y = e.y;
x -=canvas.offsetLeft;
y -=canvas.offsetTop;
alert("x:" +x+ "y:"+y);
}
//this function will draw on the canvas for me!
function draw()
{
context.fillStyle = 'grey';
context.fillRect(0, 0, canvas.width, canvas.height);
}
// pX and pY are the parameters are going to be used so that the inside of the house body becomes the drawing canvas.
function drawHouse(pX ,pY)
{
//body
context.beginPath();
context.fillStyle = '#ffffff';
context.strokeStyle = "black";
context.lineWidth = "5";
context.rect(pX,pY, 160,110);
context.closePath();
context.fill();
context.stroke();
//roof
context.beginPath();
context.fillStyle = "red";
context.moveTo(pX,pY-1);;
context.lineTo(pX+80, pY-95);
context.lineTo(pX+160, pY-1);
context.closePath();
context.fill();
context.stroke();
//door
context.beginPath();
context.fillStyle = "green";
context.fillSStyle = "red";
context.strokeStyle = "black";
context.rect(pX+55,pY+30, 50, 80);
context.fill();
context.stroke();
//handle
var radius = 5;
context.beginPath();
context.arc(pX+93, pY+75, radius, 0, 2 * Math.PI, false);
context.fillStyle = 'purple';
context.fill();
context.lineWidth = 3;
context.strokeStyle = 'black';
context.stroke();
//window Left
context.beginPath();
context.fillStyle = 'blue';
context.strokeStyle = "black";
context.rect(pX+12,pY+30, 30, 60);
context.fill();
context.stroke();
//window Filler left vertically
context.beginPath();
context.moveTo(pX+26.5,pY+30);
context.lineTo(pX+26.5, pY+90);
context.fill();
context.stroke();
//Window filler left horizontally
context.beginPath();
context.moveTo(pX+41, pY+60);
context.lineTo(pX+11,pY+60);
context.fill();
context.stroke();
//Window Right
context.beginPath();
context.fillStyle = 'blue';
context.strokeStyle = "black";
context.rect(pX+117,pY+30, 30, 60);
context.fill();
context.stroke();
//window filler right vertically
context.beginPath();
context.moveTo(pX+131.5,pY+30);
context.lineTo(pX+131.5, pY+90);
context.fill();
context.stroke();
//window Filler right horizontally
context.beginPath();
context.moveTo(pX+147, pY+60);
context.lineTo(pX+117,pY+60);
context.fill();
context.stroke();
}
initialise();
draw();
for(var i=0; i < 5; i++)
{
var pX=0+160*i;
for(var b=0; b < 5; b++)
{
var pY=100+210*b;
drawHouse(pX,pY);
}
}
}
Add a parameter to drawHouse:
function drawHouse(pX, pY, drawGreen) {
// ...
if (drawGreen)
context.fillStyle = "green";
else
context.fillSStyle = "red";
// ...
}
And then, pass it accordingly. For example:
// before your loop
var paintGreen = false;
// In the inner for
var pY=100+210*b;
drawHouse(pX,pY,paintGreen);
paintGreen = !paintGreen; // alternate
Im starting to learn canvas and i just hit my first frustrating situation, im trying to make a clipping mask of a .jpg src in a triangle. Everything looks fine until i restore my context and try to add any other Path... my clipping mask appears to not exist anymore.
Here is my code :
<script>
function init() {
var canvas = document.getElementById('myCanvas');
if(canvas.getContext) {
var context = canvas.getContext('2d');
var imageObj = new Image();
imageObj.src = 'stephgopro2.jpg';
// triangle coordonate
context.save();
context.beginPath;
context.moveTo(100, 0);
context.lineTo(0, 100);
context.lineTo(200, 100);
context.lineTo(100, 0);
context.clip();
imageObj.onload = function() {
context.drawImage(imageObj, 0, 0, 300, 170);
};
context.restore();
context.beginPath();
context.fillStyle = '#333';
context.rect(0, 0, 600, 200);
context.fill();
}
}
</script>
</head>
<body onload='init()'>
<canvas id="myCanvas" width="600" height="200"></canvas>
</body>
Can you please help me with that? many thanks.
The image is loaded asynchronously so the context has already been restored before the image is drawn to the canvas. If you update the code as follows you'll get (what I think are) the results you expect:
function init() {
var canvas = document.getElementById('myCanvas');
if(canvas.getContext) {
var context = canvas.getContext('2d');
var imageObj = new Image();
imageObj.src = 'assets/1.jpg';
// triangle coordonate
context.save();
context.beginPath();
context.moveTo(100, 0);
context.lineTo(0, 100);
context.lineTo(200, 100);
context.lineTo(100, 0);
context.stroke();
context.clip();
imageObj.onload = function() {
context.drawImage(imageObj, 0, 0, 300, 170);
// Restore the context and continue drawing now the image has been drawn
context.restore();
context.beginPath();
context.fillStyle = '#333';
context.rect(0, 0, 600, 200);
context.fill();
};
}
}
I am just trying my hands at HTML5's most talked feature i.e canvas. There are 2 rectangles and I only want to rotate 1st and keep the 2nd one as it is. Problem is when the below code runs my whole canvas is rotated and both rectangles are rotated. I can't even find any API where I can get reference to the object that I have drawn and rotate only that specific object instead of the whole context.
Code:
<script type="text/javascript">
var context;
var radian = 0.01;
var w, h;
$(document).ready(function () {
w = document.width;
h = document.height;
var canvas = $('#canvas');
context = canvas[0].getContext('2d');
canvas[0].width = w;
canvas[0].height = h;
setInterval(startAnim, 200);
});
function startAnim() {
context.clearRect(0, 0, w, h);
context.strokeStyle = 'rgb(0,0,0)';
context.fillStyle = 'rgb(0,0,0)';
context.fillRect(0, 0, w, h);
context.strokeStyle = 'rgb(0,0,0)';
context.fillStyle = 'rgb(255,255,0)';
context.rotate(radian);
context.strokeRect(400, 300, 200, 200);
context.fillRect(400, 300, 200, 200);
context.fillStyle = 'rgb(0,255,255)';
context.fillRect(500, 400, 200, 200);
radian += 0.01;
}
</script>
How can I prevent this from happening?
Finally, I have resolved the issue on my own by trial and error. This is the code:
<script type="text/javascript">
var context;
var radian = 0.01;
var w, h;
$(document).ready(function () {
w = document.width;
h = document.height;
var canvas = $('#canvas');
context = canvas[0].getContext('2d');
canvas[0].width = w;
canvas[0].height = h;
setInterval(startAnim, 100);
});
function startAnim() {
context.save();
context.strokeStyle = 'rgb(0,0,0)';
context.fillStyle = 'rgb(0,0,0)';
context.fillRect(0, 0, w, h);
context.rotate(radian);
context.strokeStyle = 'rgb(0,0,0)';
context.fillStyle = 'rgb(255,255,0)';
context.strokeRect(400, 300, 200, 200);
context.fillRect(400, 300, 200, 200);
context.restore();
context.fillStyle = 'rgb(0,255,255)';
context.fillRect(500, 400, 200, 200);
radian += 0.1;
}
</script>
As I understand you have to clear the whole canvas and redraw everything, between each frame. Keep the data for the rectangles in memory. Do the context.clearRect(0, 0, w, h); between each frame, then draw the rectangles again with there new altered properties.
For example, I have a canvas in a page with some kind of a path. It is created by javascript this way:
var context = $('#some_canvas').getContext('2d');
context.beginPath();
context.lineWidth = 5;
context.strokeStyle = '#000000';
context.moveTo(0, 0);
context.lineTo(100, 100);
context.stroke();
Is there a way to make the path that appears after this command to have some tiled background image?
I believe you're looking for the createPattern() method:
var pattern = new Image;
pattern.src = "data:image/png;base64,iVBORw0KGgoAAAANSUhEUgAAABAAAAARCAIAAABbzbuTAAAAGXRFWHRTb2Z0d2FyZQBBZG9iZSBJbWFnZVJlYWR5ccllPAAAAZtJREFUeNqMUs+rAVEUvjNG2MhClOUsppSEjbWFpOwtMIv5B2ZhZqkkZKkpe+XPYKtsbSxsZIGaQpgi4r3Pu5p3eV45dW/nnPt959zzg5RKpU6n8/WxkHq9LghCs9n8lICjKAohpFwuf0LgcCzLSqfTo9FIVVVd10He7XbX6/V8Pu/3e47jcB+Px0AgkEqlCOXNZjNJkgB1/wg+6XA4ACXPomkasXM1Gg3yj4AZi8WAHgwGgu1dLpcvOKRKJBLZbDaTyYDgdDrvXjtDLpd7yT6dTv8WzdNnaPP53A6Mezgc+v3+N/+jvO12GwwGqQfFYJRQksnker1+MwfIZDLxeDwA+Xy+xWIBT6VSgYk+Hg4HlvAoerVaodNQ8vl8KBSCUqvVAG2326g4EolsNhuYGNQjQ6/XAwh9GI/HbDxZltn/o2OPDBgctaPRKIsQRZEqWJxisXg3aaRCoQBvv99nw59Op3A4DH+1Wu12u09FYwh4w/6wBGwUOhuPx6FfLpfb7fZbtGEYpmnyPM/+x+v1tlotl8sFHdtFnd8CDACAg6Y2weEZQQAAAABJRU5ErkJggg==";
pattern.onload = function () {
var context = $('#some_canvas').getContext('2d');
context.beginPath();
context.lineWidth = 16;
context.strokeStyle = context.createPattern(pattern, 'repeat');
context.moveTo(0, 0);
context.lineTo(150, 150);
context.stroke();
};