Adjust Canvas Size To Orientation

indian_lincoln · June 21, 2017, 2:14pm

I’m pretty new to programming and I’ve been following this tutorial for making a simple drawing app in Ionic.

Here is a link to the tutorial I was using: https://www.joshmorony.com/creating-a-drawing-application-in-ionic/

I followed the tutorial and was able to make it work. However when I test it on my browser using ionic serve and responsive device mode the canvas doesn’t adjust after starting to draw when changing the orientation. I start drawing in portrait view and then when I flip the orientation or landscape and start drawing again I can clearly see the cut off point of the canvas.

I’ve attached screenshots and the code below.

canvas-draw.html

<ion-toolbar id="top-toolbar">
  <ion-buttons left>
    <button *ngFor="let colour of availableColours" icon-only ion-button (click)="changeColour(colour)">
      <ion-icon [style.color]="colour" name="brush"></ion-icon>
    </button>
  </ion-buttons>
  <ion-buttons right>
    <button style="border: 1px solid #cecece;" ion-button icon-only style.color="#fff" (click)="changeColour('#fff')">
      <ion-icon style="color: #fff;" name="square"></ion-icon>
    </button>
  </ion-buttons>
</ion-toolbar>

<canvas #myCanvas (touchstart)="handleStart($event)" (touchmove)="handleMove($event)" (touched)="handleEnd($event)"></canvas>

<ion-toolbar id="bottom-toolbar">
  <ion-buttons left>
    <button color="dark" ion-button icon-only (click)="clearCanvas()"><ion-icon name="trash"></ion-icon></button>
  </ion-buttons>
  <ion-buttons right>
    <button color="dark" ion-button icon-only (click)="changeSize(5)"><ion-icon style="font-size: 0.25em;" name="radio-button-on"></ion-icon></button>
    <button color="dark" ion-button icon-only (click)="changeSize(10)"><ion-icon style="font-size: 0.5em;" name="radio-button-on"></ion-icon></button>
    <button color="dark" ion-button icon-only (click)="changeSize(20)"><ion-icon style="font-size: 1em;" name="radio-button-on"></ion-icon></button>
    <button color="dark" ion-button icon-only (click)="changeSize(50)"><ion-icon style="font-size: 2em;" name="radio-button-on"></ion-icon></button>
    <button color="dark" ion-button icon-only (click)="changeSize(200)"><ion-icon style="font-size: 3em;" name="radio-button-on"></ion-icon></button>
  </ion-buttons>
</ion-toolbar>

canvas-draw.module.ts

import { NgModule } from '@angular/core';
import { IonicPageModule } from 'ionic-angular';
import { CanvasDraw } from './canvas-draw';

@NgModule({
  declarations: [
    CanvasDraw,
  ],
  imports: [
    IonicPageModule.forChild(CanvasDraw),
  ],
  exports: [
    CanvasDraw
  ]
})
export class CanvasDrawComponentModule {}

canvas-draw.scss

canvas-draw {
    height: 100%;
    width: 100%;
    display: block;
    #top-toolbar{
        position: absolute;
        top: 0;
    }
    #bottom-toolbar{
        position: absolute;
        bottom: 0;
    }
}

canvas-draw.ts

import { Component,ViewChild,Renderer } from '@angular/core';
import { Platform } from 'ionic-angular';

@Component({
  selector: 'canvas-draw',
  templateUrl: 'canvas-draw.html'
})
export class CanvasDraw {
    @ViewChild('myCanvas') canvas: any;

    canvasElement: any;
    lastX: number;
    lastY: number;

    currentColour: string = '#1abc9c';
    availableColours: any;

    brushSize: number = 10;

    constructor(public platform: Platform, public renderer: Renderer) {
        console.log('Hello CanvasDraw Component');

        this.availableColours = [
            '#1abc9c',
            '#3498db',
            '#9b59b6',
            '#e67e22',
            '#e74c3c'
        ];

    }

    ngAfterViewInit(){

        this.canvasElement = this.canvas.nativeElement;

        this.renderer.setElementAttribute(this.canvasElement, 'width', this.platform.width() + '');
        this.renderer.setElementAttribute(this.canvasElement, 'height', this.platform.height() + '');

    }

    changeColour(colour){
        this.currentColour = colour;
    }

    changeSize(size){
        this.brushSize = size;
    }

    handleStart(ev){

        this.lastX = ev.touches[0].pageX;
        this.lastY = ev.touches[0].pageY;
    }

    handleMove(ev){

        let ctx = this.canvasElement.getContext('2d');
        let currentX = ev.touches[0].pageX;
        let currentY = ev.touches[0].pageY;

        ctx.beginPath();
        ctx.lineJoin = "round";
        ctx.moveTo(this.lastX, this.lastY);
        ctx.lineTo(currentX, currentY);
        ctx.closePath();
        ctx.strokeStyle = this.currentColour;
        ctx.lineWidth = this.brushSize;
        ctx.stroke();       

        this.lastX = currentX;
        this.lastY = currentY;

    }

    handleEnd(ev){

        console.log(ev);
    }

    clearCanvas(){
        let ctx = this.canvasElement.getContext('2d');
        ctx.clearRect(0, 0, this.canvasElement.width, this.canvasElement.height);   
    }

}

Screenshots

First I’m drawing in portrait view.

Then flip the orientation and I continue drawing but you can see where the canvas is cut off.