JavaScript Paint App Finished
In this part I finish my JavaScript Paint App. In this part I finish my JavaScript Paint App. It can draw brush strokes, lines, rectangles, circles, ellipses, and polygons. The app also saves and loads new images. When I cover other libraries and frameworks in the future like Node I will add additional capabilities.
All of the code and a transcript of the video follows below. Take notes as you watch to help you learn. I hope you have enjoyed the tutorial.
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Code & Transcript
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// JavaScript Paint App JavaScript Canvas API // 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 whether I'm currently using brush let usingBrush = false; // Stores line x & ys used to make brush lines let brushXPoints = new Array(); let brushYPoints = new Array(); // Stores whether mouse is down let brushDownPos = new Array(); // 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 getPolygonPoints(){ // Get angle in radians based on x & y of mouse location let angle = degreesToRadians(getAngleUsingXAndY(loc.x, loc.y)); // X & Y for the X & Y point representing the radius is equal to // the X & Y of the bounding rubberband box let radiusX = shapeBoundingBox.width; let radiusY = shapeBoundingBox.height; // Stores all points in the polygon let polygonPoints = []; // Each point in the polygon is found by breaking the // parts of the polygon into triangles // Then I can use the known angle and adjacent side length // to find the X = mouseLoc.x + radiusX * Sin(angle) // You find the Y = mouseLoc.y + radiusY * Cos(angle) for(let i = 0; i < polygonSides; i++){ polygonPoints.push(new PolygonPoint(loc.x + radiusX * Math.sin(angle), loc.y - radiusY * Math.cos(angle))); // 2 * PI equals 360 degrees // Divide 360 into parts based on how many polygon // sides you want angle += 2 * Math.PI / polygonSides; } return polygonPoints; } // Get the polygon points and draw the polygon function getPolygon(){ let polygonPoints = getPolygonPoints(); ctx.beginPath(); ctx.moveTo(polygonPoints[0].x, polygonPoints[0].y); for(let i = 1; i < polygonSides; i++){ ctx.lineTo(polygonPoints[i].x, polygonPoints[i].y); } ctx.closePath(); } // Called to draw the line function drawRubberbandShape(loc){ ctx.strokeStyle = strokeColor; ctx.fillStyle = fillColor; if(currentTool === "brush"){ // Create paint brush DrawBrush(); } else if(currentTool === "line"){ // Draw Line ctx.beginPath(); ctx.moveTo(mousedown.x, mousedown.y); ctx.lineTo(loc.x, loc.y); ctx.stroke(); } else if(currentTool === "rectangle"){ // Creates rectangles ctx.strokeRect(shapeBoundingBox.left, shapeBoundingBox.top, shapeBoundingBox.width, shapeBoundingBox.height); } else if(currentTool === "circle"){ // Create circles let radius = shapeBoundingBox.width; ctx.beginPath(); ctx.arc(mousedown.x, mousedown.y, radius, 0, Math.PI * 2); ctx.stroke(); } else if(currentTool === "ellipse"){ // Create ellipses // ctx.ellipse(x, y, radiusX, radiusY, rotation, startAngle, endAngle) let radiusX = shapeBoundingBox.width / 2; let radiusY = shapeBoundingBox.height / 2; ctx.beginPath(); ctx.ellipse(mousedown.x, mousedown.y, radiusX, radiusY, Math.PI / 4, 0, Math.PI * 2); ctx.stroke(); } else if(currentTool === "polygon"){ // Create polygons getPolygon(); ctx.stroke(); } } function UpdateRubberbandOnMove(loc){ // Stores changing height, width, x & y position of most // top left point being either the click or mouse location UpdateRubberbandSizeData(loc); // Redraw the shape drawRubberbandShape(loc); } // Store each point as the mouse moves and whether the mouse // button is currently being dragged function AddBrushPoint(x, y, mouseDown){ brushXPoints.push(x); brushYPoints.push(y); // Store true that mouse is down brushDownPos.push(mouseDown); } // Cycle through all brush points and connect them with lines function DrawBrush(){ for(let i = 1; i < brushXPoints.length; i++){ ctx.beginPath(); // Check if the mouse button was down at this point // and if so continue drawing if(brushDownPos[i]){ ctx.moveTo(brushXPoints[i-1], brushYPoints[i-1]); } else { ctx.moveTo(brushXPoints[i]-1, brushYPoints[i]); } ctx.lineTo(brushXPoints[i], brushYPoints[i]); ctx.closePath(); ctx.stroke(); } } 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; // Brush will store points in an array if(currentTool === 'brush'){ usingBrush = true; AddBrushPoint(loc.x, loc.y); } }; function ReactToMouseMove(e){ canvas.style.cursor = "crosshair"; loc = GetMousePosition(e.clientX, e.clientY); // If using brush tool and dragging store each point if(currentTool === 'brush' && dragging && usingBrush){ // Throw away brush drawings that occur outside of the canvas if(loc.x > 0 && loc.x < canvasWidth && loc.y > 0 && loc.y < canvasHeight){ AddBrushPoint(loc.x, loc.y, true); } RedrawCanvasImage(); DrawBrush(); } else { if(dragging){ RedrawCanvasImage(); UpdateRubberbandOnMove(loc); } } }; 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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