Introduction

In this article, we are going to understand the creation of graphical equation representations using the HTML 5 canvas. In this section of this article, we will perform a graphical equation by setting up the co-ordinate geometry within the canvas tag and its properties.
A Graphical equation displays when the application runs in the browser. Here we will use some JavaScript and some styles along with HTML code. Just go through the steps to see how to create this application.
Let's see how the CanvasGraphEquation application can be created. To do so use the following steps.
Step 1 : Open a HTML editor or Visual Studio. Open File menu ->select new ->Choose Website
0000.jpg
This is where we will create an HTML5 application.
canvasg1.png
Step 2: In this section, we will create the style for the media and create the .css on the media screen. Put the given script in the Head section of the HTML or between the <head>--</head> tags. Here the CSS is used for design purposes.
CSS Script
  1. <style>
  2. body
  3. {
  4. margin: 0px;
  5. padding: 0px;
  6. }
  7. Canvas
  8. {
  9. border: 2px solid #9C9898;
  10. margin-top: 50px;
  11. margin-left: 50px;
  12. background-color: #F4D19F;
  13. box-shadow: 5px 5px 8px #222;
  14. }
  15. .title
  16. {
  17. text-align: center;
  18. font-family: Segoe UI Light, Arial, Helvetica;
  19. font-size: 2.2em;
  20. margin: 1em;
  21. }
  22. .info
  23. {
  24. text-align: center;
  25. font-family: Segoe UI Light, Arial, Helvetica;
  26. font-size: 1.2em;
  27. margin: 0.25em;
  28. }
  29. </style>
Step 3: In this part, we need to work on some JavaScript. To fully understand how JavaScript works, download the attached .rar file and run the CanvasGraphEquation application.
The whole JavaScript looks as in the following:
  1. <script>
  2. function Graph(config)
  3. {
  4. // user defined properties
  5. this.canvas = document.getElementById(config.canvasId);
  6. this.minX = config.minX;
  7. this.minY = config.minY;
  8. this.maxX = config.maxX;
  9. this.maxY = config.maxY;
  10. this.unitsPerTick = config.unitsPerTick;
  11. // constants
  12. this.axisColor = "#aaa";
  13. this.font = "8pt Calibri";
  14. this.tickSize = 20;
  15. // relationships
  16. this.context = this.canvas.getContext("2d");
  17. this.rangeX = this.maxX - this.minX;
  18. this.rangeY = this.maxY - this.minY;
  19. this.unitX = this.canvas.width / this.rangeX;
  20. this.unitY = this.canvas.height / this.rangeY;
  21. this.centerY = Math.round(Math.abs(this.minY / this.rangeY) * this.canvas.height);
  22. this.centerX = Math.round(Math.abs(this.minX / this.rangeX) * this.canvas.width);
  23. this.iteration = (this.maxX - this.minX) / 1000;
  24. this.scaleX = this.canvas.width / this.rangeX;
  25. this.scaleY = this.canvas.height / this.rangeY;
  26. // draw x and y axis
  27. this.drawXAxis();
  28. this.drawYAxis();
  29. }
  30. Graph.prototype.drawXAxis = function ()
  31. {
  32. var context = this.context;
  33. context.save();
  34. context.beginPath();
  35. context.moveTo(0, this.centerY);
  36. context.lineTo(this.canvas.width, this.centerY);
  37. context.strokeStyle = this.axisColor;
  38. context.lineWidth = 2;
  39. context.stroke();
  40. // draw tick marks
  41. var xPosIncrement = this.unitsPerTick * this.unitX;
  42. var xPos, unit;
  43. context.font = this.font;
  44. context.textAlign = "center";
  45. context.textBaseline = "top";
  46. // draw left tick marks
  47. xPos = this.centerX - xPosIncrement;
  48. unit = -1 * this.unitsPerTick;
  49. while (xPos > 0)
  50. {
  51. context.moveTo(xPos, this.centerY - this.tickSize / 2);
  52. context.lineTo(xPos, this.centerY + this.tickSize / 2);
  53. context.stroke();
  54. context.fillText(unit, xPos, this.centerY + this.tickSize / 2 + 3);
  55. unit -= this.unitsPerTick;
  56. xPos = Math.round(xPos - xPosIncrement);
  57. }
  58. // draw right tick marks
  59. xPos = this.centerX + xPosIncrement;
  60. unit = this.unitsPerTick;
  61. while (xPos < this.canvas.width)
  62. {
  63. context.moveTo(xPos, this.centerY - this.tickSize / 2);
  64. context.lineTo(xPos, this.centerY + this.tickSize / 2);
  65. context.stroke();
  66. context.fillText(unit, xPos, this.centerY + this.tickSize / 2 + 3);
  67. unit += this.unitsPerTick;
  68. xPos = Math.round(xPos + xPosIncrement);
  69. }
  70. context.restore();
  71. };
  72. window.onload = function ()
  73. {
  74. var myGraph = new Graph({
  75. canvasId: "myCanvas",
  76. minX: -10,
  77. minY: -10,
  78. maxX: 10,
  79. maxY: 10,
  80. unitsPerTick: 1
  81. });
  82. myGraph.drawEquation(function (x)
  83. {
  84. return 5 * Math.sin(x);
  85. }, "yellow", 3);
  86. myGraph.drawEquation(function (x)
  87. {
  88. return x * x;
  89. }, "orange", 3);
  90. myGraph.drawEquation(function (x)
  91. {
  92. return 1 * x;
  93. }, "green", 3);
  94. };
  95. </script>
Step 4: In this section we are going to become familiar with the body part of HTML scripting. Replace this script from the body section of the canvasgraphicalequation.aspx page. Here we pass a Canvas in the canvas tag.
  1. <body style="background-color: #C9E0E6">
  2. <center>
  3. <h1>
  4. Canvas Graphical Equation Representation
  5. </h1>
  6. </center>
  7. <hr />
  8. <canvas id="myCanvas" width="578" height="300">
  9. </canvas>
  10. </body>
Step 5: The complete code for the CanvasGraphEquation application.
  1. <%@ Page Language="C#" AutoEventWireup="true" CodeBehind="canvasgraphicalequation.aspx.cs" Inherits="CanvasGraphEquation._Default" %>
  2. <!DOCTYPE html PUBLIC "-//W3C//DTD XHTML 1.0 Transitional//EN" "http://www.w3.org/TR/xhtml1/DTD/xhtml1-transitional.dtd">
  3. <html xmlns="http://www.w3.org/1999/xhtml">
  4. <head runat="server">
  5. <style>
  6. </style>
  7. <script>
  8. </script>
  9. </head>
  10. <body style="background-color: #C9E0E6">
  11. <center>
  12. <h1>
  13. Canvas Graphical Equation Representation
  14. </h1>
  15. </center>
  16. <hr />
  17. <canvas id="myCanvas" width="578" height="300">
  18. </canvas>
  19. </body>
  20. </html>
Step 6: Output Press F5
Note: For the accurate output of HTML5 applications, you must have the Google Chrome browser on your PC. A Graphical equation displays when the application runs on the browser.
canvasg.png
Here are some useful resources