In this article you'll learn how to draw in the canvas a point according to the clicked point by the user. To draw points on a canvas when the user clicks on it, we need to retrieve the click event and get the coordinates of that click. To get the mouse coordinates relative to an HTML5 Canvas, we can create a getPosition method which returns the mouse coordinates x,y based on the position of the client mouse and the position of the canvas obtained from the getBoundingClientRect method of the window object.
Now, our drawCoordinates method will draw the point according to the location of the click in the canvas.
This receives as first parameter the x horizontal coordinate of the canvas and as second parameter the y vertical coordinate relative to the canvas. The following fidle shows an already working example of all the above methods. Go to the Result tab and see how it works, draw many points on the hen! This code is friendly with all the resolutions as it's kept the most simple as possible.1.3: Shapes & Drawing - umu.bl5115hamba.pw Tutorial
The dark mode beta is finally here. Change your preferences any time. Stack Overflow for Teams is a private, secure spot for you and your coworkers to find and share information. For a drawing application, I'm saving the mouse movement coordinates to an array then drawing them with lineTo. The resulting line is not smooth. How can I produce a single curve between all the gathered points? I've googled but I have only found 3 functions for drawing lines: For 2 sample points, simply use lineTo.
For 3 sample points quadraticCurveTofor 4 sample points, bezierCurveTo. I tried drawing a bezierCurveTo for every 4 points in the array, but this leads to kinks every 4 sample points, instead of a continuous smooth curve.
The problem with joining subsequent sample points together with disjoint "curveTo" type functions, is that where the curves meet is not smooth. This is because the two curves share an end point but are influenced by completely disjoint control points.
One solution is to "curve to" the midpoints between the next 2 subsequent sample points. Joining the curves using these new interpolated points gives a smooth transition at the end points what is an end point for one iteration becomes a control point for the next iteration.
In other words the two disjointed curves have much more in common now. This solution was extracted out of the book "Foundation ActionScript 3. Note: this solution does not actually draw through each of the points, which was the title of my question rather it approximates the curve through the sample points but never goes through the sample pointsbut for my purposes a drawing applicationit's good enough for me and visually you can't tell the difference.
You can achieve smooth lines by using cardinal splines aka canonical spline to draw smooth curves that goes through the points. I made this function for canvas - it's split into three function to increase versatility.
The main wrapper function looks like this:. To draw a curve have an array with x, y points in the order: x1,y1, x2,y2,Now that we have set up our canvas environmentwe can get into the details of how to draw on the canvas.
By the end of this article, you will have learned how to draw rectangles, triangles, lines, arcs and curves, providing familiarity with some of the basic shapes. Working with paths is essential when drawing objects onto the canvas and we will see how that can be done. Before we can start drawing, we need to talk about the canvas grid or coordinate space.
Our HTML skeleton from the previous page had a canvas element pixels wide and pixels high.
To the right, you see this canvas with the default grid overlayed. Normally 1 unit in the grid corresponds to 1 pixel on the canvas. The origin of this grid is positioned in the top left corner at coordinate 0,0. All elements are placed relative to this origin. So the position of the top left corner of the blue square becomes x pixels from the left and y pixels from the top, at coordinate x,y. Later in this tutorial we'll see how we can translate the origin to a different position, rotate the grid and even scale it, but for now we'll stick to the default.
All other shapes must be created by combining one or more paths. Luckily, we have an assortment of path drawing functions which make it possible to compose very complex shapes. Each of these three functions takes the same parameters. Below is the draw function from the previous page, but now it is making use of these three functions.
The fillRect function draws a large black square pixels on each side. The clearRect function then erases a 60x60 pixel square from the center, and then strokeRect is called to create a rectangular outline 50x50 pixels within the cleared square. In upcoming pages we'll see two alternative methods for clearRectand we'll also see how to change the color and stroke style of the rendered shapes.
Unlike the path functions we'll see in the next section, all three rectangle functions draw immediately to the canvas. Now let's look at paths. A path is a list of points, connected by segments of lines that can be of different shapes, curved or not, of different width and of different color.
A path, or even a subpath, can be closed. The first step to create a path is to call the beginPath.The CanvasRenderingContext2D method lineTopart of the Canvas 2D API, adds a straight line to the current sub-path by connecting the sub-path's last point to the specified x, y coordinates. Like other methods that modify the current path, this method does not directly render anything.
To draw the path onto a canvas, you can use the fill or stroke methods. Each call of lineTo and similar methods automatically adds to the current sub-path, which means that all the lines will all be stroked or filled together.
This example draws a letter 'M' with a single contiguous line. Get the latest and greatest from MDN delivered straight to your inbox. Sign in to enjoy the benefits of an MDN account. The compatibility table on this page is generated from structured data.
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Stack Overflow for Teams is a private, secure spot for you and your coworkers to find and share information. DEMO HERE showing how to draw the most complicated element on your example which has one field with lines branching to two other fields.
There's some great tutorials HERE. Learn more. Draw lines between 2 elements in html page Ask Question. Asked 6 years, 1 month ago. Active 2 years, 10 months ago. Viewed 47k times. JPG i wondered what the best way do this using canvas and html5 using background image.
When and will the image change? Are the lines straight or curve? Do they need to be changed dynamically? And any user interactions required e. Possible duplicate of How to draw a line between two divs? Active Oldest Votes.
How it basically works is as follows. Start the drawing function with: context. Aaron Aaron 2, 5 5 gold badges 27 27 silver badges 46 46 bronze badges. BruceWayne BruceWayne 1 1 silver badge 7 7 bronze badges.
Sign up or log in Sign up using Google. Sign up using Facebook. Sign up using Email and Password. Post as a guest Name. Email Required, but never shown. The Overflow Blog. Podcast Programming tutorials can be a real drag.It is renderer agnostic enabling the same api to draw in multiple contexts: svgcanvasand webgl.
Development Version Uncompressed with comments about kb.
Production Version Minified using Closure Compiler about 50kb. Prior to v0. If you're already loading these files elsewhere then you can build the project yourself and get the file size even smaller. For more information on custom builds check out the source on github.
As a result, two. At its core two. This means that when you draw or create an object a Two. Path or Two. Grouptwo actually stores and remembers that. After you make the object you can apply any number of operations to it — e.
It is simple in nature and can be automated or paired with another animation library. For more information check out the examples. This means developers and designers alike can create SVG elements in commercial applications like Adobe Illustrator and bring them into your two. In order to start any of these demos you'll want to download two. When you visit the page, you should be able to open up the console and type Two. If this returns a function then you're ready to begin! Before we get into all the fancy animating it's good to get a feel for how to make shapes in two.
In order to do this we need to have an instance of two. This sets up a dom element that contains either an svg or canvas element to add to the webpage. The two object has a scene which holds all shapes as well as methods for creating shapes.
For a list of all properties and construction parameters check out the documentation. Adding shapes to groups makes managing multiple shapes easier and more sane. Group's provide an easy way to move your content through translationrotationand scale.
These operations emit from the coordinate space 0, 0. In the example below we can see that the initial orientation of the circle and rectangle changed from the first example. These shapes are oriented around 0, 0which allows us to transform the group around the centeroid of the shapes.
In addition Group's styling operations trickle down and apply to each shape. All rendered objects in two. Every two instance has a property scene.
This property is a root-level Two. Group and can act as a camera through the same transformations described above. Finally, let's add some motion to our shapes.
The first idea that may strike you is to generate a serie of DIV of 1px per 1px to draw the line. It works, it's dead simple and extremely short. Alas it's slow and generates a hell lot of useless tags, not to mention the difficulty to move a line. Of course it can be optimized a bit using some Bresenham line algorithms and making use of symetry, etc The key to get a fast script, is to do the minimum.
Trying to figure the common factors of the lines we saw above will lead us in that direction. Try to project mentally the lines on the small edge of their bounding box. It should ring a bell.
Any line can be reproduced by stretching a diagonal. If you need more to be convinced, just look the figure below. So what we need is to figure the width and height of the bouding box, and the direction of the line and size of the small edge.
Both things can be considered if we only use some diagonnals whose size is a power of 2, that is : 1, 2, 4, 8, 16, 32, 64, Ok, it will introduce some small stretching artifacts but that's a small price to pay to move the lines in realtime. Getting the position of the bounding box and the size of its smaller edge is staight forward.
Calculating the direction of the line corresponds more or less to compute in which quadrant of a circle it is pointing. Pixel perfect precision can be achieved at the price of having all possible diagonals. It takes a lot more time, and connections, to preload the images but the end result look nicer and is slightly faster than the quirk method above.
The number of applications is endless: route annotations on maps, drawing app, measuring tool, games, Don't be shy; get in touch by mailtwittergithublinkedin or pouet if you have any questions, feedback, speaking, workshop or performance opportunity.