Question
Answer and Explanation
Creating a dashed line on a canvas using CreateJS involves utilizing the graphics API provided by CreateJS. Unlike native HTML5 canvas, CreateJS doesn't have a direct property for dashed lines. Instead, you need to emulate the effect by drawing alternating lines and gaps. Here's how you can achieve it:
1. Set Up the Canvas and Stage:
- First, you need to create a canvas element and initialize a CreateJS Stage. This provides the environment to draw on.
2. Create a Graphics Object:
- Obtain a graphics object from a Shape instance, which will allow you to use the drawing methods to create the dashed line.
3. Define Dashed Line Parameters:
- Decide the length of the dashes and the gaps between them. These parameters will be the key to defining your dashed line.
4. Implement the Dashed Line Logic:
- You will move your "pen" along the path and periodically toggle drawing on and off to create a dash-gap pattern. This requires an algorithm to repeatedly move and either draw or move with the pen up depending on the dash pattern.
5. Example Code to Create a Dashed Line:
<canvas id="myCanvas" width="500" height="200"></canvas>
<script src="https://code.createjs.com/1.0.0/createjs.min.js"></script>
<script>
document.addEventListener("DOMContentLoaded", function() {
const canvas = document.getElementById("myCanvas");
const stage = new createjs.Stage(canvas);
const shape = new createjs.Shape();
const graphics = shape.graphics;
const x1 = 50, y1 = 100;
const x2 = 450, y2 = 100;
const dashLength = 10;
const gapLength = 5;
const color = "#000000";
const thickness = 2;
graphics.setStrokeStyle(thickness);
graphics.beginStroke(color);
let currentX = x1;
let currentY = y1;
let distance = Math.sqrt(Math.pow(x2-x1, 2) + Math.pow(y2-y1, 2));
let angle = Math.atan2(y2-y1, x2-x1);
let drawing = true;
while (currentX <= x2 && distance > 0) {
if (drawing) {
let nextX = currentX + Math.cos(angle) dashLength;
let nextY = currentY + Math.sin(angle) dashLength;
if(nextX > x2){
nextX = x2;
nextY = y2;
}
graphics.lineTo(nextX, nextY);
currentX = nextX;
currentY = nextY;
} else {
let nextX = currentX + Math.cos(angle) gapLength;
let nextY = currentY + Math.sin(angle) gapLength;
if(nextX > x2){
nextX = x2;
nextY = y2;
}
graphics.moveTo(nextX, nextY);
currentX = nextX;
currentY = nextY;
}
drawing = !drawing;
distance = Math.sqrt(Math.pow(x2-currentX, 2) + Math.pow(y2-currentY, 2));
}
graphics.endStroke();
stage.addChild(shape);
stage.update();
});
</script>
6. Add Shape to Stage and Update:
- Finally, add the shape to the stage, and call stage.update() to render the changes.
7. Customization:
- Feel free to adjust parameters like dashLength, gapLength, color, thickness or the line's starting and ending points to achieve the desired look and feel. You can also modify it to create different types of dashed lines (e.g. dot patterns by reducing dashLength).
By using this approach you will be able to create a dashed line on the canvas with CreateJS, by emulating it's behaviour via a loop and different drawing actions.