In this part of my JavaScript Paint App tutorial I make the toolbar work, show how to get canvas mouse positions, save / redraw the canvas, create the rubber band system, find angles, convert to radians / degrees, save / import images and set up event handling. In the next video I’ll finish the whole app.
All of the code used is available below to help you learn. Here are the images used.
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Code from the Video
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JSTUT7.JS // Reference to the canvas element let canvas; // Context provides functions used for drawing and // working with Canvas let ctx; // Stores previously drawn image data to restore after // new drawings are added let savedImageData; // Stores whether I'm currently dragging the mouse let dragging = false; let strokeColor = 'black'; let fillColor = 'black'; let line_Width = 2; let polygonSides = 6; // Tool currently using let currentTool = 'brush'; let canvasWidth = 600; let canvasHeight = 600; // Stores size data used to create rubber band shapes // that will redraw as the user moves the mouse class ShapeBoundingBox{ constructor(left, top, width, height) { this.left = left; this.top = top; this.width = width; this.height = height; } } // Holds x & y position where clicked class MouseDownPos{ constructor(x,y) { this.x = x, this.y = y; } } // Holds x & y location of the mouse class Location{ constructor(x,y) { this.x = x, this.y = y; } } // Holds x & y polygon point values class PolygonPoint{ constructor(x,y) { this.x = x, this.y = y; } } // Stores top left x & y and size of rubber band box let shapeBoundingBox = new ShapeBoundingBox(0,0,0,0); // Holds x & y position where clicked let mousedown = new MouseDownPos(0,0); // Holds x & y location of the mouse let loc = new Location(0,0); // Call for our function to execute when page is loaded document.addEventListener('DOMContentLoaded', setupCanvas); function setupCanvas(){ // Get reference to canvas element canvas = document.getElementById('my-canvas'); // Get methods for manipulating the canvas ctx = canvas.getContext('2d'); ctx.strokeStyle = strokeColor; ctx.lineWidth = line_Width; // Execute ReactToMouseDown when the mouse is clicked canvas.addEventListener("mousedown", ReactToMouseDown); // Execute ReactToMouseMove when the mouse is clicked canvas.addEventListener("mousemove", ReactToMouseMove); // Execute ReactToMouseUp when the mouse is clicked canvas.addEventListener("mouseup", ReactToMouseUp); } function ChangeTool(toolClicked){ document.getElementById("open").className = ""; document.getElementById("save").className = ""; document.getElementById("brush").className = ""; document.getElementById("line").className = ""; document.getElementById("rectangle").className = ""; document.getElementById("circle").className = ""; document.getElementById("ellipse").className = ""; document.getElementById("polygon").className = ""; // Highlight the last selected tool on toolbar document.getElementById(toolClicked).className = "selected"; // Change current tool used for drawing currentTool = toolClicked; } // Returns mouse x & y position based on canvas position in page function GetMousePosition(x,y){ // Get canvas size and position in web page let canvasSizeData = canvas.getBoundingClientRect(); return { x: (x - canvasSizeData.left) * (canvas.width / canvasSizeData.width), y: (y - canvasSizeData.top) * (canvas.height / canvasSizeData.height) }; } function SaveCanvasImage(){ // Save image savedImageData = ctx.getImageData(0,0,canvas.width,canvas.height); } function RedrawCanvasImage(){ // Restore image ctx.putImageData(savedImageData,0,0); } function UpdateRubberbandSizeData(loc){ // Height & width are the difference between were clicked // and current mouse position shapeBoundingBox.width = Math.abs(loc.x - mousedown.x); shapeBoundingBox.height = Math.abs(loc.y - mousedown.y); // If mouse is below where mouse was clicked originally if(loc.x > mousedown.x){ // Store mousedown because it is farthest left shapeBoundingBox.left = mousedown.x; } else { // Store mouse location because it is most left shapeBoundingBox.left = loc.x; } // If mouse location is below where clicked originally if(loc.y > mousedown.y){ // Store mousedown because it is closer to the top // of the canvas shapeBoundingBox.top = mousedown.y; } else { // Otherwise store mouse position shapeBoundingBox.top = loc.y; } } // Returns the angle using x and y // x = Adjacent Side // y = Opposite Side // Tan(Angle) = Opposite / Adjacent // Angle = ArcTan(Opposite / Adjacent) function getAngleUsingXAndY(mouselocX, mouselocY){ let adjacent = mousedown.x - mouselocX; let opposite = mousedown.y - mouselocY; return radiansToDegrees(Math.atan2(opposite, adjacent)); } function radiansToDegrees(rad){ if(rad < 0){ // Correct the bottom error by adding the negative // angle to 360 to get the correct result around // the whole circle return (360.0 + (rad * (180 / Math.PI))).toFixed(2); } else { return (rad * (180 / Math.PI)).toFixed(2); } } // Converts degrees to radians function degreesToRadians(degrees){ return degrees * (Math.PI / 180); } function ReactToMouseDown(e){ // Change the mouse pointer to a crosshair canvas.style.cursor = "crosshair"; // Store location loc = GetMousePosition(e.clientX, e.clientY); // Save the current canvas image SaveCanvasImage(); // Store mouse position when clicked mousedown.x = loc.x; mousedown.y = loc.y; // Store that yes the mouse is being held down dragging = true; } }; function ReactToMouseMove(e){ canvas.style.cursor = "crosshair"; loc = GetMousePosition(e.clientX, e.clientY); }; function ReactToMouseUp(e){ canvas.style.cursor = "default"; loc = GetMousePosition(e.clientX, e.clientY); RedrawCanvasImage(); UpdateRubberbandOnMove(loc); dragging = false; usingBrush = false; } // Saves the image in your default download directory function SaveImage(){ // Get a reference to the link element var imageFile = document.getElementById("img-file"); // Set that you want to download the image when link is clicked imageFile.setAttribute('download', 'image.png'); // Reference the image in canvas for download imageFile.setAttribute('href', canvas.toDataURL()); } function OpenImage(){ let img = new Image(); // Once the image is loaded clear the canvas and draw it img.onload = function(){ ctx.clearRect(0,0,canvas.width, canvas.height); ctx.drawImage(img,0,0); } img.src = 'image.png'; } JSTUT7.HTML <!doctype html> <html lang="en"> <head> <meta charset="utf-8"> <meta name="viewport" content="width = device-width, initial-scale = 1"> <title>JavaScript Paint App</title> <link rel="stylesheet" type="text/css" href="mainstyle.css"> <script src="jscolor.js"></script> <script src="jstut7-2.js"></script> </head> <body> <div class="wrapper"> <div class="toolbar"> <a class="selected" href="#" id="open" onclick="OpenImage()"><img src="open-icon.png"></a> <a href="#" id="save" onclick="SaveImage()"><img src="save-icon.png"></a> <a href="#" id="brush" onclick="ChangeTool('brush')"><img src="brush-icon.png"></a> <a href="#" id="line" onclick="ChangeTool('line')"><img src="line-icon.png"></a> <a href="#" id="rectangle" onclick="ChangeTool('rectangle')"><img src="rectangle-icon.png"></a> <a href="#" id="circle" onclick="ChangeTool('circle')"><img src="circle-icon.png"></a> <a href="#" id="ellipse" onclick="ChangeTool('ellipse')"><img src="ellipse-icon.png"></a> <a href="#" id="polygon" onclick="ChangeTool('polygon')"><img src="polygon-icon.png"></a> </div><br> <canvas id="my-canvas" width="600" height="600"></canvas> <div id="img-data-div"> <a href="#" id="img-file" download="image.png">download image</a> </div> </div> </body> </html> MAINSTYLE.CSS .wrapper { max-width: 900px; margin: auto; font-family: "Arial"; } .toolbar{ width: 100%; background-color: #444444; overflow: auto; } .toolbar a { float: left; width: 11%; text-align: center; padding: 6px 5px; transition: all 0.5s ease; color: white; } /* Change color on hover */ .toolbar a:hover { background-color: #000; } /* Change color on selected icon */ .selected { background-color: #000; } #my-canvas{ width: 100%; border: 3px solid #000000; } #img-data-div{ width: 100%; max-width: 900px; height: 200px; } /* Resize image to container */ .toolbar a img{ max-width:100%; height:auto; } |
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