Computer programming. Intro to programming. Animation basics. Interactive programs. Becoming a community coder. Bonus: Resizing with variables. Logic and if Statements. Debugging programs. Writing clean code. Object-Oriented Design.
If you're new here, watch our intro video and get a brief tour of our programming course. Then get coding! What is Programming? Learning programming on Khan Academy. Drawing basics. Making drawings with code. Quick tip: number scrubbing. Challenge: Simple snowman. Drawing more shapes with code.Images can be displayed inside a canvas, where they can be integrated with the vector-drawing techniques of the canvas API. You can also select a portion of an image to display and apply the various transformations to your image to create interesting compositions and animations.
Top left corner of source: The first job is to choose the part of the original picture that will be displayed.
The next two parameters indicate the top left corner of a selection on the original picture. You might use an image editor like Gimp or IrfanView to determine the selection position and size.
Height and width of source: The next two parameters indicate the height and width of the source selection. Size of destination: The last two parameters describe the size of the destination image on the canvas.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.
Internally, paths are stored as a list of sub-paths lines, arcs, etc which together form a shape. Every time this method is called, the list is reset and we can start drawing new shapes.
The second step is calling the methods that actually specify the paths to be drawn. We'll see these shortly. The third, and an optional step, is to call closePath. This method tries to close the shape by drawing a straight line from the current point to the start.
If the shape has already been closed or there's only one point in the list, this function does nothing. One very useful function, which doesn't actually draw anything but becomes part of the path list described above, is the moveTo function. You can probably best think of this as lifting a pen or pencil from one spot on a piece of paper and placing it on the next. When the canvas is initialized or beginPath is called, you typically will want to use the moveTo function to place the starting point somewhere else.
We could also use moveTo to draw unconnected paths. Take a look at the smiley face below. To try this for yourself, you can use the code snippet below.This article provides an introduction to canvas, and further resources to allow you to learn more. As we talked about in our HTML Multimedia and embedding module, the Web was originally just text, which was very boring, so images were introduced — first via the element embeds an image into the document. This however was still not enough.
This became WebGLwhich gained traction among browser vendors, and was standardized around — WebGL allows you to create real 3D graphics inside your web browser; the below example shows a simple rotating WebGL cube:. This article will focus mainly on 2D canvas, as raw WebGL code is very complex. This element is used to define the area on the page into which the image will be drawn.
This is as simple as including the element on the page:. Inside the canvas tags, you can put some fallback content, which is shown if the user's browser doesn't support canvas.
Of course, the above message is really unhelpful! In a real example you'd want to relate the fallback content to the canvas content. For example, if you were rendering a constantly updating graph of stock prices, the fallback content could be a static image of the latest stock graph, with alt text saying what the prices are in text. Canvases with no explicit width and height default to pixels wide by pixels high.
We need to do one final thing before we can consider our canvas template finished. To draw onto the canvas we need to get a special reference to the drawing area called a context. So that's it — our canvas is now primed and ready for drawing on! The ctx variable now contains a CanvasRenderingContext2D object, and all drawing operations on the canvas will involve manipulating this object. Let's do one last thing before we move on.
Using Canviz has advantages for your web application over generating and sending bitmapped images and image maps to the browser as the server only needs to have Graphviz generate xdot text; this is faster than generating bitmapped images.
Flotr enables you to draw appealing graphs in most modern browsers with an easy to learn syntax. It comes with great features like legend support, negative value support, mouse tracking, selection support, zoom support, event hooks, CSS styling support and much more.
From there, you can add all kinds of other features like giving the user the ability to choose a line thickness, color, brush strokes, and even layers.
Active 3 months ago. Viewed k times. Please help me how can I do? Please give some source code. Thank you. Han 5 5 silver badges 18 18 bronze badges. MartinJoo MartinJoo 2, 7 7 gold badges 26 26 silver badges 36 36 bronze badges. See also: How do I hand draw on canvas? Active Oldest Votes. Here is a working sample. Why do you do switch?
I'm trying to use this code, but have issues with the drawing being off vertically when I'm not scrolled all the way down on the page.
The client software is a graph component with an optional application wrapper that is integrated into an existing web interface. The client requires a web server to deliver the required files to the client or can be run from the local filesystem without a web server. The backends may be used as is, or they may be embedded into an existing server application in one of the supported languages.
The API is very well documented to make sure you can start using in no time. We covered extensively GoJS in this post.