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Javascript Html5 Canvas Draw Circle

This article will tell you how to employ Html5 canvas and javascript to draw a rectangle and a circle.

ane. Use Html5 Sheet To Draw Rectangle Steps.

  1. Get the Html5 canvas object in javascript.
    var rectCanvas = document.getElementById(id);
  2. Change the canvas backdrop such every bit width, peak, style, etc.
    rectCanvas.width = windowWidth;  rectCanvas.fashion.display = 'block';
  3. Get the 2d context object from the canvas object.
    var ctx = rectCanvas.getContext('second');
  4. Set the rectangle make full color.
    ctx.fillStyle = "yellow";
  5. Clear the rectangle in the canvas.
    ctx.clearRect(rectX, rectY, rectWidth, rectHeight);
  6. Fill the rectangle in the canvas with the specified color.
    ctx.fillRect(rectX, rectY, rectWidth, rectHeight)
  7. Set up the stroke rectangle border color.
    ctx.strokeStyle = "blueish";
  8. Fix the stroke rectangle border line width.
    ctx.lineWidth = strokeBorderLineWidth;
  9. Draw the stroke rectangle with the provided border colour and line width.
    ctx.strokeRect(rectX, rectY, rectWidth, rectHeight)
  10. Below is the case rectangle prototype.
    html5-canvas-draw-rectangle-example

ii. Use Html5 Canvass To Draw Circumvolve Steps.

  1. Go the Html5 canvas object by id.
    var circleCanvas = certificate.getElementById(id);
  2. Modify the canvas object attributes.
    circleCanvas.width = window.innerWidth; circleCanvas.height = window.innerHeight; circleCanvas.style.brandish = "cake";
  3. Become the canvas 2d context object.
    var ctx = circleCanvas.getContext('2d');
  4. Call the context object's beginPath() method to create the path.
    ctx.beginPath();
  5. Draw the radians or circle using the context object's arc() method.
    ctx.arc(circleCenterX, circleCenterY, circleRadius, startAngle, endAngle, truthful);
  6. Close path by invoking the context object's closePath() method.
    ctx.closePath();
  7. Set up the circumvolve color.
    ctx.fillStyle = "cherry-red";
  8. Fill up the circle with the to a higher place colour.
    ctx.fill();
  9. Set the stroke circle border color.
    ctx.strokeStyle = "greenish";
  10. Set the stroke circle edge line width.
    ctx.lineWidth = ten;
  11. Depict the stroke circumvolve.
    ctx.stroke();
  12. Below is the circle image.
    html5-canvas-draw-circle-example-1
  13. There is as well another example that shows how to draw multiple circles using Html5 canvas, below is the example epitome.
    html5-canvas-draw-multiple-circles-example

3. Html5 Employ Sheet To Draw Rectangle & Circle Examples.

  1. The example demo video URL is https://youtu.exist/PbOhUrss1QE.
  2. This example contains 2 files html5-canvas-draw-rectangle-circle.html, html5-canvas-draw-rectangle-circle.js.
  3. On the Html file's onload event, it will telephone call the initialize_canvas() method to hibernate all the Html5 canvas on the web folio.
  4. When you lot click the Draw button, information technology will draw a rectangle or circle below the button, and the button's text volition exist inverse to Remove. When you click the Remove push button, it will hide the rectangle or circle canvas.
  5. html5-canvas-draw-rectangle-circumvolve.html.
    <!DOCTYPE html> <html> <head> <meta charset="ISO-8859-ane"> <title>How To Use Html5 Canvas To Draw Rectangle And Circle</title> <script type="text/javascript" src="html5-sheet-draw-rectangle-circumvolve.js" charset="utf-8"></script>  <mode> canvas{     display:block; } </style>  </head> <body onload="initialize_canvas()">  <h3>Case Of Draw Rectangle Utilise Html5 Canvas.</h3> <div>     <input type="button" id="describe-rectangle-button" value="Depict Rectangle" onclick="drawRectangle('rectangle-canvas', this)" />     <canvas id="rectangle-canvas"></sheet> </div>   <h3>Example Of Draw Circumvolve Use Html5 Sheet.</h3> <div>     <input type="button" id="draw-circle-button" value="Draw Circumvolve" onclick="drawCircle('circle-canvass', this)" />     <canvas id="circumvolve-canvas"></canvas> </div>  <h3>Example Of Describe Multiple Circles Use Html5 Canvas.</h3> <div>     <input type="button" id="draw-multiple-circles-button" value="Draw Multiple Circles" onclick="drawMultipleCircles('multiple-circles-canvas', this)" />     <sail id="multiple-circles-sail"></sheet> </div> </body> </html>
  6. html5-canvas-draw-rectangle-circle.js.
    /**  *   */  // Initialize all the Html sheet objects on the Html page. function initialize_canvas(){          // Become all the canvas object listing.     canvasList = document.getElementsByTagName('sail');          // Get the sail object list length.     length = canvasList.length;          // Loop all the canvas objects in the list.     for(var i=0; i < length; i++){                  // Become each cnavas object.         canvasObj = canvasList[i];         // Hide the canvas object by setting information technology's display style aspect to 'none'.         canvasObj.style.display = 'none';     } }  /* This function demo how to draw a rectangle using canvas.  */ part drawRectangle(id, src){              /*       Summate the destination rectangle object left, top, width, height values.     */     // The rectangle width and acme percent number of the window's width and elevation.     rectSizePercentage = 0.3;          // Get the web browser window's width, meridian value.     windowWidth = window.innerWidth;     windowHeight = window.innerHeight;          // Set the stroke border line width.     strokeBorderLineWidth = 10;          // Get the rectangle left, pinnacle coordinate value.     rectX = strokeBorderLineWidth;     rectY = strokeBorderLineWidth;     // Calculate the rectangle width and height value.     rectWidth = parseInt(windowWidth*rectSizePercentage);     rectHeight = parseInt(windowHeight*rectSizePercentage);          // Get the Html5 Sheet object.     var rectCanvas = certificate.getElementById(id);     // If not establish the Sheet object then return false.     if(rectCanvas==null){                  return false;              }          // Get the canvas display style value.     canvasDisplay = rectCanvas.style.brandish;          if(canvasDisplay == 'none'){                  src.value = "Remove Rectangle";                  // You should first modify the Canvas object attributes such every bit width, summit, style.         // Then you tin can call the canvasObject.getContext('2d') to get the Canvas context object.         // If you modify the Canvass object'southward attributes afterward yous become the Canvass object's context,          // then yous will find the change does non take effect.         rectCanvas.width = windowWidth;         rectCanvas.height = windowHeight*(rectSizePercentage + 0.05);         // Set the canvas object's display style to 'block' to display it.         rectCanvas.style.display = 'block';	                  // Go the Canvass context object after modify it's attributes.         var ctx = rectCanvas.getContext('second');                  // Then you can alter the context attribute.         ctx.fillStyle = "yellow";                  // You should clear canvass after you change it's size to avert draw black color canvas event.         ctx.clearRect(rectX, rectY, rectWidth, rectHeight);                  // Draw the rectangle and fill the colour.         ctx.fillRect(rectX, rectY, rectWidth, rectHeight)                  // Ready the stroke rectangle ( rectamgle without fill color and only has a border ) style color.         ctx.strokeStyle = "blue";                  // Gear up the stroke rectangle edge line width.         ctx.lineWidth = strokeBorderLineWidth;                  // Describe the stoke rectangle.         ctx.strokeRect(rectX, rectY, rectWidth, rectHeight)                  console.log('window.innerWidth = ' + window.innerWidth);                  console.log('window.innerHeight = ' + window.innerHeight);                  panel.log('rectX = ' + rectX);                  console.log('rectY = ' + rectY);                  console.log('rectWidth = ' + rectWidth);                  console.log('rectHeight = ' + rectHeight);              }else if(canvasDisplay == 'cake'){                  src.value = "Draw Rectangle";                  rectCanvas.way.brandish = 'none';     } }   /* This function demo how to describe a circle using canvass.  */ function drawCircle(id, src){          // Become the Html5 Canvas object.     var circleCanvas = document.getElementById(id);     // If not found the Sail object so render fake.     if(circleCanvas==nada){                  return false;              }          // Become the canvas display style value.     canvasDisplay = circleCanvas.fashion.brandish;          if(canvasDisplay == 'none'){                  circleCanvas.width = window.innerWidth;         circleCanvas.superlative = window.innerHeight*0.3;         circleCanvas.manner.display = "block";	                  src.value = "Remove Circle";                  // Get the Canvas context object later on modify it'south attributes.         var ctx = circleCanvas.getContext('2d');                  // Phone call the context object's beginPath() method to create the path.         ctx.beginPath();                  // Define the circumvolve eye point coordinates.         circleCenterX = 100;         circleCenterY = 100;         circleRadius = xc;         startAngle = 0;         endAngle = Math.PI * 2;                  // Describe the radians or circle using the context object'due south arc() method.         ctx.arc(circleCenterX, circleCenterY, circleRadius, startAngle, endAngle, truthful);                  // Close path by invoking the context object'due south closePath() method.         ctx.closePath();                   // Set the circle color.         ctx.fillStyle = "cherry";                  // Fill the circle with the above colour.         ctx.fill();	                  // Set the stroke circumvolve border color.         ctx.strokeStyle = "green";                  // Ready the stroke circle border line width.         ctx.lineWidth = 10;                  // Draw the stroke circle.         ctx.stroke();              }else if(canvasDisplay == 'cake'){                  src.value = "Draw Circle";                  circleCanvas.fashion.display = 'none';     }      }   /* This function demo how to draw multiple circles using sail.  */ office drawMultipleCircles(id, src){          // Get the canvas object first.     var sail = document.getElementById(id);          if(sheet==null){         render faux;     }          // Go the canvas display style value.     canvasDisplay = canvass.style.display;          if(canvasDisplay == 'none'){                  sail.width = window.innerWidth*0.5;         canvas.tiptop = window.innerHeight*0.5;         sheet.style.display = "block";	                  src.value = "Remove Multiple Circles";                  // Get the Canvas context object after alter it's attributes.         var ctx = canvas.getContext('2d');                  ctx.fillStyle = "blueish";                  ctx.fillRect(0, 0, canvas.width, canvass.acme);                           for(var i=0;i<10;i++)         {             // Phone call the context object's beginPath() method to create the path.             ctx.beginPath();                      // Define the circle center indicate coordinates.             circleCenterX = i*25;             circleCenterY = i*25;             circleRadius = i*ten;             startAngle = 0;             endAngle = Math.PI * 2;                      // Depict the radians or circle using the context object'due south arc() method.             ctx.arc(circleCenterX, circleCenterY, circleRadius, startAngle, endAngle, truthful);                      // Close path by invoking the context object's closePath() method.             ctx.closePath();                       // Set the circle colour.             ctx.fillStyle = "yellow";                      // Fill the circle with the higher up color.             ctx.make full();	         }               }else if(canvasDisplay == 'block'){                  src.value = "Depict Multiple Circles";                  canvas.style.display = 'none';     } }

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Source: https://www.dev2qa.com/how-to-use-html5-canvas-to-draw-rectangle-and-circle/