Draw rectangle on mousedown event












0














I have a basic zoomable and pannable canvas build in Fabric.js. I need to draw a rectangle on every mousedown event at the clicked coordinate position. The problem happens when the canvas is transformed from it's initial state - the drawing is not accurate because the coordinates must be transformed with the new matrix.



How can I transform the coordinates from the mouse event using the new matrix?



Here is the code I am using. Thanks



canvas.on('mouse:down', function (opt) {

  const evt = opt.e;

  const p = new fabric.Rect({

    left: opt.e.offsetX,

    top: opt.e.offsetY,

    fill: 'red',

    width: 30,

    height: 30,

  });

  canvas.add(p);

});


Update 1: I found a method to transform points (fabric.util.transformPoint()), but
the transformed points were not correct according to the canvas context.



  const evt = opt.e;

  const point = new fabric.Point(opt.e.offsetX, opt.e.offsetY);

  const transformedPoint = fabric.util.transformPoint(point, this.viewportTransform);

  const p = new fabric.Rect({

    left: transformedPoint.x,

    top: transformedPoint.y,

    fill: 'red',

    width: 30,

    height: 30,

  });

  this.add(p);





javascript html5-canvas fabricjs







share|improve this question
























  • What do you mean by 'it isn't working for me'?
    – Konowy
    Nov 19 '18 at 23:32










  • Sorry, I meant that the transformed points were not correct according to the canvas context (using fabric.util.transformPoint())
    – xepe
    Nov 20 '18 at 9:15
















0














I have a basic zoomable and pannable canvas build in Fabric.js. I need to draw a rectangle on every mousedown event at the clicked coordinate position. The problem happens when the canvas is transformed from it's initial state - the drawing is not accurate because the coordinates must be transformed with the new matrix.



How can I transform the coordinates from the mouse event using the new matrix?



Here is the code I am using. Thanks



canvas.on('mouse:down', function (opt) {

  const evt = opt.e;

  const p = new fabric.Rect({

    left: opt.e.offsetX,

    top: opt.e.offsetY,

    fill: 'red',

    width: 30,

    height: 30,

  });

  canvas.add(p);

});


Update 1: I found a method to transform points (fabric.util.transformPoint()), but
the transformed points were not correct according to the canvas context.



  const evt = opt.e;

  const point = new fabric.Point(opt.e.offsetX, opt.e.offsetY);

  const transformedPoint = fabric.util.transformPoint(point, this.viewportTransform);

  const p = new fabric.Rect({

    left: transformedPoint.x,

    top: transformedPoint.y,

    fill: 'red',

    width: 30,

    height: 30,

  });

  this.add(p);





javascript html5-canvas fabricjs







share|improve this question
























  • What do you mean by 'it isn't working for me'?
    – Konowy
    Nov 19 '18 at 23:32










  • Sorry, I meant that the transformed points were not correct according to the canvas context (using fabric.util.transformPoint())
    – xepe
    Nov 20 '18 at 9:15














0












0








0







I have a basic zoomable and pannable canvas build in Fabric.js. I need to draw a rectangle on every mousedown event at the clicked coordinate position. The problem happens when the canvas is transformed from it's initial state - the drawing is not accurate because the coordinates must be transformed with the new matrix.



How can I transform the coordinates from the mouse event using the new matrix?



Here is the code I am using. Thanks



canvas.on('mouse:down', function (opt) {

  const evt = opt.e;

  const p = new fabric.Rect({

    left: opt.e.offsetX,

    top: opt.e.offsetY,

    fill: 'red',

    width: 30,

    height: 30,

  });

  canvas.add(p);

});


Update 1: I found a method to transform points (fabric.util.transformPoint()), but
the transformed points were not correct according to the canvas context.



  const evt = opt.e;

  const point = new fabric.Point(opt.e.offsetX, opt.e.offsetY);

  const transformedPoint = fabric.util.transformPoint(point, this.viewportTransform);

  const p = new fabric.Rect({

    left: transformedPoint.x,

    top: transformedPoint.y,

    fill: 'red',

    width: 30,

    height: 30,

  });

  this.add(p);





javascript html5-canvas fabricjs







share|improve this question















I have a basic zoomable and pannable canvas build in Fabric.js. I need to draw a rectangle on every mousedown event at the clicked coordinate position. The problem happens when the canvas is transformed from it's initial state - the drawing is not accurate because the coordinates must be transformed with the new matrix.



How can I transform the coordinates from the mouse event using the new matrix?



Here is the code I am using. Thanks



canvas.on('mouse:down', function (opt) {

  const evt = opt.e;

  const p = new fabric.Rect({

    left: opt.e.offsetX,

    top: opt.e.offsetY,

    fill: 'red',

    width: 30,

    height: 30,

  });

  canvas.add(p);

});


Update 1: I found a method to transform points (fabric.util.transformPoint()), but
the transformed points were not correct according to the canvas context.



  const evt = opt.e;

  const point = new fabric.Point(opt.e.offsetX, opt.e.offsetY);

  const transformedPoint = fabric.util.transformPoint(point, this.viewportTransform);

  const p = new fabric.Rect({

    left: transformedPoint.x,

    top: transformedPoint.y,

    fill: 'red',

    width: 30,

    height: 30,

  });

  this.add(p);





javascript html5-canvas fabricjs




javascript html5-canvas fabricjs






share|improve this question















share|improve this question













share|improve this question




share|improve this question








edited Nov 20 '18 at 9:28







xepe

















asked Nov 19 '18 at 20:58









xepexepe

5016




5016












  • What do you mean by 'it isn't working for me'?
    – Konowy
    Nov 19 '18 at 23:32










  • Sorry, I meant that the transformed points were not correct according to the canvas context (using fabric.util.transformPoint())
    – xepe
    Nov 20 '18 at 9:15


















  • What do you mean by 'it isn't working for me'?
    – Konowy
    Nov 19 '18 at 23:32










  • Sorry, I meant that the transformed points were not correct according to the canvas context (using fabric.util.transformPoint())
    – xepe
    Nov 20 '18 at 9:15
















What do you mean by 'it isn't working for me'?
– Konowy
Nov 19 '18 at 23:32




What do you mean by 'it isn't working for me'?
– Konowy
Nov 19 '18 at 23:32












Sorry, I meant that the transformed points were not correct according to the canvas context (using fabric.util.transformPoint())
– xepe
Nov 20 '18 at 9:15




Sorry, I meant that the transformed points were not correct according to the canvas context (using fabric.util.transformPoint())
– xepe
Nov 20 '18 at 9:15












1 Answer
1






active

oldest

votes


















1














I finally solved it using fabric.util.transformPoint() using an inverted matrix. Here is the code for transforming a point in the canvas to a point in the canvas context.



  const point = new fabric.Point(offsetX, offsetY);

  const invertedMatrix = fabric.util.invertTransform(canvas.viewportTransform)

  const transformedPoint = fabric.util.transformPoint(point, invertedMatrix);





share|improve this answer





















    Your Answer






    StackExchange.ifUsing("editor", function () {
    StackExchange.using("externalEditor", function () {
    StackExchange.using("snippets", function () {
    StackExchange.snippets.init();
    });
    });
    }, "code-snippets");

    StackExchange.ready(function() {
    var channelOptions = {
    tags: "".split(" "),
    id: "1"
    };
    initTagRenderer("".split(" "), "".split(" "), channelOptions);

    StackExchange.using("externalEditor", function() {
    // Have to fire editor after snippets, if snippets enabled
    if (StackExchange.settings.snippets.snippetsEnabled) {
    StackExchange.using("snippets", function() {
    createEditor();
    });
    }
    else {
    createEditor();
    }
    });

    function createEditor() {
    StackExchange.prepareEditor({
    heartbeatType: 'answer',
    autoActivateHeartbeat: false,
    convertImagesToLinks: true,
    noModals: true,
    showLowRepImageUploadWarning: true,
    reputationToPostImages: 10,
    bindNavPrevention: true,
    postfix: "",
    imageUploader: {
    brandingHtml: "Powered by u003ca class="icon-imgur-white" href="https://imgur.com/"u003eu003c/au003e",
    contentPolicyHtml: "User contributions licensed under u003ca href="https://creativecommons.org/licenses/by-sa/3.0/"u003ecc by-sa 3.0 with attribution requiredu003c/au003e u003ca href="https://stackoverflow.com/legal/content-policy"u003e(content policy)u003c/au003e",
    allowUrls: true
    },
    onDemand: true,
    discardSelector: ".discard-answer"
    ,immediatelyShowMarkdownHelp:true
    });


    }
    });














    draft saved

    draft discarded


















    StackExchange.ready(
    function () {
    StackExchange.openid.initPostLogin('.new-post-login', 'https%3a%2f%2fstackoverflow.com%2fquestions%2f53382527%2fdraw-rectangle-on-mousedown-event%23new-answer', 'question_page');
    }
    );

    Post as a guest















    Required, but never shown

























    1 Answer
    1






    active

    oldest

    votes








    1 Answer
    1






    active

    oldest

    votes









    active

    oldest

    votes






    active

    oldest

    votes









    1














    I finally solved it using fabric.util.transformPoint() using an inverted matrix. Here is the code for transforming a point in the canvas to a point in the canvas context.



      const point = new fabric.Point(offsetX, offsetY);
    
  const invertedMatrix = fabric.util.invertTransform(canvas.viewportTransform)
    
  const transformedPoint = fabric.util.transformPoint(point, invertedMatrix);





    share|improve this answer


























      1














      I finally solved it using fabric.util.transformPoint() using an inverted matrix. Here is the code for transforming a point in the canvas to a point in the canvas context.



        const point = new fabric.Point(offsetX, offsetY);
      
  const invertedMatrix = fabric.util.invertTransform(canvas.viewportTransform)
      
  const transformedPoint = fabric.util.transformPoint(point, invertedMatrix);





      share|improve this answer
























        1












        1








        1






        I finally solved it using fabric.util.transformPoint() using an inverted matrix. Here is the code for transforming a point in the canvas to a point in the canvas context.



          const point = new fabric.Point(offsetX, offsetY);
        
  const invertedMatrix = fabric.util.invertTransform(canvas.viewportTransform)
        
  const transformedPoint = fabric.util.transformPoint(point, invertedMatrix);





        share|improve this answer












        I finally solved it using fabric.util.transformPoint() using an inverted matrix. Here is the code for transforming a point in the canvas to a point in the canvas context.



          const point = new fabric.Point(offsetX, offsetY);
        
  const invertedMatrix = fabric.util.invertTransform(canvas.viewportTransform)
        
  const transformedPoint = fabric.util.transformPoint(point, invertedMatrix);






        share|improve this answer












        share|improve this answer



        share|improve this answer










        answered Nov 20 '18 at 9:22









        xepexepe

        5016




        5016






























            draft saved

            draft discarded




















































            Thanks for contributing an answer to Stack Overflow!


            • Please be sure to answer the question. Provide details and share your research!

            But avoid …



            • Asking for help, clarification, or responding to other answers.

            • Making statements based on opinion; back them up with references or personal experience.


            To learn more, see our tips on writing great answers.




            draft saved


            draft discarded














            StackExchange.ready(
            function () {
            StackExchange.openid.initPostLogin('.new-post-login', 'https%3a%2f%2fstackoverflow.com%2fquestions%2f53382527%2fdraw-rectangle-on-mousedown-event%23new-answer', 'question_page');
            }
            );

            Post as a guest















            Required, but never shown





















































            Required, but never shown














            Required, but never shown












            Required, but never shown







            Required, but never shown

































            Required, but never shown














            Required, but never shown












            Required, but never shown







            Required, but never shown







            Popular posts from this blog

            android studio warns about leanback feature tag usage required on manifest while using Unity exported app?

            Image
            .everyoneloves__top-leaderboard:empty,.everyoneloves__mid-leaderboard:empty,.everyoneloves__bot-mid-leaderboard:empty{ height:90px;width:728px;box-sizing:border-box; } 0 This is a simple project showing cubes on Unity, exported to android project and imported on Android studio. On maifest file it showed following warning: Expecting <uses-feature android:name="android.software.leanback" android:required="false" /> tag I have no information about it. And also on default emptyview android project does not use/mention this feature. I know it is required by TV's and such but why its not added by default? Why is this? And Should I concern about it? android unity3d
            Read more

            SQL update select statement

            Image
            0 I'm trying to update an entry in my database (postgresql). I'm having a problem with updating the query: INSERT INTO prices (price, product_id) SELECT product_price, commn_id FROM products_temp as prod WHERE NOT EXISTS (SELECT * FROM prices od WHERE prod.commn_id = od.product_id) OR prod.product_price != ( SELECT price FROM prices as p WHERE p.product_id = prod.commn_id order by p.end desc LIMIT 1 ) Query works fine when i delete: OR prod.product_price != ( SELECT price FROM prices as p WHERE p.product_id = prod.commn_id order by p.end desc LIMIT 1 ) So it seems to me that it's looping through this operation. My question is, how can I fix it? sql postgresql
            Read more

            'app-layout' is not a known element: how to share Component with different Modules

            Image
            0 My application was working fine until I decided to go with lazy loading: So, my shared component looks like this: import { Component, Renderer2 } from '@angular/core'; export interface FormModel { captcha?: string; } @Component({ selector: 'app-layout', templateUrl: './app-layout.component.html', styleUrls: ['./app-layout.css'] }) export class FullLayoutComponent { } app-layout.component.ts I am using this component in my Another component say school-home.component.html like this: <app-layout> </app-layout> and it was working fine until I created a Module school-home.module.ts like this: import { NgModule } from '@angular/core'; import { CommonModule } from '@angular/common'; import { SchoolhomeRoutingModule
            Read more