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Ramazan Kornilov
Ramazan Kornilov

React Draw Shapes


All react-konva components correspond to Konva components of the same name.All the parameters available for Konva objects are valid props forcorresponding react-konva components, unless noted otherwise.




react draw shapes



is an HTML element that helps you to draw shapes. You can draw shapes inside a canvas element using the Canvas API provided by your browser. This element acts as a container in which you can draw different shapes. To draw inside a canvas element, a context for the element is required. A context is an entity that we can draw shapes on. We can use getContext to get the CanvasRenderingContext2D that returns the 2-D context.


The process that we are going to follow is very similar to what we had in the Square component. In the square component, we made use of the onClick attribute of the canvas element to draw a rectangle on the mouse click event. Similarly, we are going to make use of the onMouseMove attribute of the canvas element.


After drawing a bit of inspiration from The Shapes of CSS I decided to see if I could remake some of these shapes with a subset of css. If you haven't been on css-tricks check them out, Chris Coyier is fantastic!


Of course we have access to react-art here so drawing shapes is pretty simple but my goal is to see if I can just use normal Views and all of the styles I have at my exposure to make as many shapes as I can off of the Shapes of CSS list.


Well we don't have the ability to do pseudo elements but they were just hacks anyway so we'll just create a wrapping View with 2 elements and style them.Now this is not exactly the same, and it's partially due to the way border-radius are managed in react-native vs the web but it's closeish.


You can add various shapes to your map. A shape is an object on the map, tied to a latitude/longitude coordinate. The following shapes are available: lines, polygons, circles and rectangles. You can also configure your shapes so that users can edit or drag them.


To draw a line on your map, use a polyline. The Polyline class defines a linear overlay of connected line segments on the map. A Polyline object consists of an array of LatLng locations, and creates a series of line segments that connect those locations in an ordered sequence.


Polyline objects are drawn as a series of straight segments on the map. You can specify custom colors, weights, and opacities for the stroke of the line within the PolylineOptions when constructing your line, or you can change those properties after construction. A polyline supports the following stroke styles:


A polygon represents an area enclosed by a closed path (or loop), which is defined by a series of coordinates. Polygon objects are similar to Polyline objects in that they consist of a series of coordinates in an ordered sequence. Polygons are drawn with a stroke and a fill. You can define custom colors, weights, and opacities for the edge of the polygon (the stroke) and custom colors and opacities for the enclosed area (the fill). Colors should be indicated in hexadecimal HTML format. Color names are not supported.


The Polygon in the example above consists of four sets of LatLng coordinates, but notice that the first and last sets define the same location, which completes the loop. In practice, however, since polygons define closed areas, you don't need to specify the last set of coordinates. The Maps JavaScript API will automatically complete the polygon by drawing a stroke connecting the last location back to the first location for any given path.


In a geodesic polyline, the segments of the polyline are drawn as the shortest path between two points on the Earth's surface, assuming the Earth is a sphere, as opposed to straight lines on the Mercator projection.


To draw a shape, set the JSON of that shape to the drawType property of the diagram and activate the drawing tool by using the tool property. The following code example illustrates how to draw a rectangle at runtime.


To draw connectors, set the JSON of the connector to the drawType property. The drawing tool can be activated by using the tool property. The following code example illustrates how to draw a straight line connector.


Now that we have set up our canvas environment, we 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 150 pixels wide and 150 pixels high.


Unlike SVG, only supports two primitive shapes: rectangles and paths (lists of points connected by lines). 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.


The fillRect() function draws a large black square 100 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.


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. To make shapes using paths, we take some extra steps:


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 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.


This method takes two arguments, x and y, which are the coordinates of the line's end point. The starting point is dependent on previously drawn paths, where the end point of the previous path is the starting point for the following, etc. The starting point can also be changed by using the moveTo() method.


This starts by calling beginPath() to start a new shape path. We then use the moveTo() method to move the starting point to the desired position. Below this, two lines are drawn which make up two sides of the triangle.


You'll notice the difference between the filled and stroked triangle. This is, as mentioned above, because shapes are automatically closed when a path is filled, but not when they are stroked. If we left out the closePath() for the stroked triangle, only two lines would have been drawn, not a complete triangle.


Let's have a more detailed look at the arc method, which takes six parameters: x and y are the coordinates of the center of the circle on which the arc should be drawn. radius is self-explanatory. The startAngle and endAngle parameters define the start and end points of the arc in radians, along the curve of the circle. These are measured from the x axis. The counterclockwise parameter is a Boolean value which, when true, draws the arc counterclockwise; otherwise, the arc is drawn clockwise.


The statement for the clockwise parameter results in the first and third row being drawn as clockwise arcs and the second and fourth row as counterclockwise arcs. Finally, the if statement makes the top half stroked arcs and the bottom half filled arcs.


Using quadratic and cubic Bézier curves can be quite challenging, because unlike vector drawing software like Adobe Illustrator, we don't have direct visual feedback as to what we're doing. This makes it pretty hard to draw complex shapes. In the following example, we'll be drawing some simple organic shapes, but if you have the time and, most of all, the patience, much more complex shapes can be created.


In addition to the three methods we saw in Drawing rectangles, which draw rectangular shapes directly to the canvas, there's also the rect() method, which adds a rectangular path to a currently open path.


We won't go over this in detail, since it's actually surprisingly simple. The most important things to note are the use of the fillStyle property on the drawing context, and the use of a utility function (in this case roundedRect()). Using utility functions for bits of drawing you do often can be very helpful and reduce the amount of code you need, as well as its complexity.


As we have seen in the last example, there can be a series of paths and drawing commands to draw objects onto your canvas. To simplify the code and to improve performance, the Path2D object, available in recent versions of browsers, lets you cache or record these drawing commands. You are able to play back your paths quickly. Let's see how we can construct a Path2D object:


In this example, we are creating a rectangle and a circle. Both are stored as a Path2D object, so that they are available for later usage. With the new Path2D API, several methods got updated to optionally accept a Path2D object to use instead of the current path. Here, stroke and fill are used with a path argument to draw both objects onto the canvas, for example. 041b061a72


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