Bounding text inside a shape - javascript

On canvas I have a background shape and text,
how do you emulate something like overflow:hidden; from css to the text?
Basically the text overflows the shape and I'm trying to mask/clip it, but couldn't find any solutions. Any ideas?

You could create a new background canvas, set its width and height to that of the desired bounding box, draw the text on it, and then draw the background canvas to the primary one.
To create a background canvas, just do
var tempCanvas = document.createElement('canvas');
but don't attach it to any other DOM node. You can then set the .width and .height of the canvas, get its context and draw on it.
To draw it back to the visible canvas, just pass the background canvas to drawImage of the main canvas context:
mainCanvas.getContext('2d').drawImage(tempCanvas, x, y);

Related

Resizing canvas with its text content

I have one canvas with some text and i want to re-size it in all directions but problem is that text content inside that canvas is getting blurred if i make it re-sizable by using css properties.
var c = document.getElementById("myCanvas");
var ctx = c.getContext("2d");
ctx.font = "30px Arial";
ctx.fillText("Hello World",10,50);
I have tried jquery re-sizable with container to canvas and resize canvas by using css but getting text content's height/width problem and also text is getting blurred.
can anyone help me please..
Yes, text has many small & tight curves whose flaws quickly become visible if you try to resize the original text. Therefore, resizing text-especially resizing larger, will always result in the texts natural "jaggies" and anti-aliasing artifacts becoming more visible.
The usual approach to canvas is to treat everything on the canvas as redrawable. Using that approach, you could clear the canvas and redraw the text using an appropriately resized font.
If your text will always appear topmost on your canvas drawings, an alternative would be to place an SVG element on top of your canvas. SVG text scales well because it is vector based, rather than pixel based. You could use the svg translate+scale to position & resize the svg text according to your scale factor. Here's a link showing how it's done: http://msdn.microsoft.com/en-us/library/gg589508(v=vs.85).aspx

Canvas element 'rubbing out' effect with JavaScript

I have a canvas <canvas></canvas> that displays a graphic of an unclean window. I need to be able to 'clean' the window with my cursor, displaying another image behind it. Just as this website uses their brushes: http://mudcu.be/sketchpad/ but rather than adding to the page, I need to remove content to display the image behind it.
Here's an example of the before and after 'rubbing out':
http://www.titaniumwebdesigns.com/images/forums/before.png http://www.titaniumwebdesigns.com/images/forums/after.png
See this complete DEMO
globalCompositeOperation is one of the most nice features in canvas api.
To achieve the desired effect, I use multiple canvas layers and globalCompositeOperation.
In this solution we have 3 layers:
Layer 1 - bottom Layer 2 - middle
Layer 3 - top
Middle and Top layers are static and only the middle layer is dynamically cleared using globalCompositeOperation.
middleCtx.globalCompositeOperation = "xor";
With globalCompositeOperation = "xor", the brush is drawn over the layer and clears the portion of canvas where it was drawn.
The final result is:
UPDATE:
To verify if the window is fully cleaned I create a hidden canvas with the same size of the others layers and drawn a black rectangle on it. When dragging the mouse over the canvas the layer 2 (middle) is cleared with a circle with transparent gradient color and now we also draw over the hidden canvas a circle with white color (might be any color different of black).
So on, we just verify the pixels of the hidden canvas and if there is no black pixels, the window is cleaned.
To get the image data we need to use something like:
imageData = context.getImageData(x, y, width, height)
and then get the pixels from the image data:
pixels = imageData.data;
The requestAnimationFrame routine is used for performance reason, because getImageData might be slow. The major change in the code is put the brush action inside an animation frame when dragging the mouse instead of do that action in each mouse move event. This allows the processor to have more time to do the pixel data verification.
Here is the modified fiddle with pixel data verification and an alert when the window is cleaned:
jsFiddle link
If you have a canvas where you have drawn a blurred image into it once, you should be able to create that effect by creating a "brush" image (an image containing a semi-transparent circle, with soft edges), and then draw that image in the canvas at the mouse coordinate using:
canvasContext.globalCompositeOperation = "destination-out";
https://developer.mozilla.org/samples/canvas-tutorial/6_1_canvas_composite.html
As soon as you have drawn the blurred image to the canvas, you just need to call the line above once and all drawn images after will use the specified composite operation.

Get elements from canvas

I would like to export my canvas onto a PDF and only render the elements added to the canvas. For example:
I have this canvas, with a background-image set to it.
http://i49.tinypic.com/n7lv.png
This is my result when I render it to PDF (using Bytescout library)
http://i50.tinypic.com/346ud7m.png
This is how I want it to end up as:
http://i50.tinypic.com/2q1s9hv.png
Meaning, I want it to end up with no rounded corners, without the background image. The canvas is done using the fabric framework. My idea is to get all the elements added to the canvas, except background image, then render the PDF from there. Any guidelines? Is that the way to go?
You simply redraw the entire scene, omitting the parts you don't want to write to a PDF.
If you don't feel like keeping track of everything to redraw, then create a second, in-memory canvas (document.createElement('canvas')) and do every drawing operation to that canvas instead of your normal one, then draw that canvas onto your normal one as the user edits instead of drawing directly onto your normal canvas.
The old way:
// First you round the corners permanently by making a clipping region:
ctx.roundedRect(etc)
ctx.clip();
//then a user draws something onto normal canvas, like an image
ctx.drawImage(myImage, 0, 0);
The new way:
// make a hidden canvas:
var hiddenCanvas = document.createElement('canvas');
var hCtx = hiddenCanvas.getContext('2d');
// First you round the corners permanently by making a clipping region:
ctx.roundedRect(etc)
ctx.clip();
//then a user draws something onto HIDDEN canvas, like an image
// This image never gets its corners cut
hCtx.drawImage(myImage, 0, 0);
// Then you draw the hidden canvas onto your normal one:
ctx.drawImage(hiddenCanvas, 0, 0);
When its time to print, you use your hidden canvas, which does not have a background image and does not have clipped corners.

Canvas shows the text blurred

I am trying to draw a sharp thin rectangle using canvas control.I want the canvas background to get loaded with an image and in foreground with some text .
Though i am able to set the color and text they are somehow appearing blurred.Is there a way to fix this issue ?
And i want to apply an image as background image for each canvas rectangle i will draw.These rectangels will appear a in a div control.So wherever there is a canvas rectangle i want its background image to be filled with the image i choose.entire div will not be filled with canvas rectangles but only half of it.Is there a way whether we can have one image for all the canvas rectangles i will draw or do ineed to draw it for every rectangle ?
html:
<div id="divBoard" >
<canvas id="canvasBoard" />
</div>
javascript:
canvas = document.getElementById("canvasBoard");
if (canvas.getContext) {
var context = canvas.getContext("2d");
}
context.fillStyle = "green";
context.fillRect(x, y, width,height);
context.font = "5px tahoma";
context.fillStyle = "black";
context.fillText("cell"+i, x, y + width);
this is the image displayed after executing my code
I have experienced the same issue with fonts not rendering as sharply on a canvas. In my project I did a workaround by placing the font in a separate DIV and overlaying it on the canvas using an appropriate z-index. This approach worked very well for me.
Have you tried adding 0.5 to x and y? The html5 canvas uses antialiasing so if you want "crisp" lines, you need to draw "in between" the pixels.
You will find a good explanation on how this works in mozilla developer reference page for lineWidth
PS. also see this question

How to resize a HTML Canvas object after creating using createElement()?

I'm creating a HTML Canvas object using this javascript code:
var Canvas = document.createElement("canvas");
Canvas.style.width = "500px";
and then i'm drawing text upon it.
When the canvas is displayed, the whole canvas has been scaled up (including content) to to match the 500px width, which results in ugly resampling. What i really want, is that the content stay the same size, only the canvas itself made bigger.
Any ideas?
Try changing the element’s width instead of its CSS width.
Canvas.width = 500;
Thomas' answer is correct, but it sound's like you also want to keep the existing content on the canvas. When you change the canvas size, it automatically gets cleared and reset to it's default state. Because of that, you will either need to redraw the contents, or copy the contents to another canvase (using drawImage), resize the canvas, then copy the contents back (again, using drawImage).

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