dinusv / paperqml

Paper.js port to qml

PaperQml

PaperQml is a port of paper.js to qml (see paper.js).

PaperQml adds vector graphics scripting to qml.

It's also used as the main library for a vector editing application at https://github.com/dinusv/papergrapherqml.

Installation

To install, simply clone the repo, and compile the sample in sample/paperqml.pro:

cd sample
qmake -r .
make (or nmake)

Usage

The sample in sample/main.qml shows how to draw simple paths, include mouse interactions and add animations.

PaperQml wraps everything around a PaperCanvas item:

PaperCanvas{
    id: paperCanvas
    width: 300
    height: 300

    onPaperReady: { // paper.js functions
        var path = new paper.Path()
        path.strokeColor = '#ff0000'
        var start = new paper.Point(100, 100)
        path.moveTo(start);
        path.lineTo(start.add([ 200, -50 ]));
        paperCanvas.paint()
    }
}

PaperCanvas also provides a qml Timer internally, so adding animations will work out of the box:

PaperCanvas{
    id: paperCanvas3
    width: 300
    height: 300

    onPaperReady: {
        var path = new paper.Path.Rectangle({
            point: [75, 75],
            size: [75, 75],
            strokeColor: 'black'
        });

        paper.view.onFrame = function(event){
            path.rotate(3);
        }
    }
}

Including PaperQml in other projects

To include PaperQml in your project, you will need to:

• Compile the JsModule class found in the src folder.

• Set it as part of the root context in jsModule when starting the application:

QQmlApplicationEngine engine;
engine.rootContext()->setContextProperty("jsModule", JsModule::provider(&engine, nullptr));

• Include and make qml/PaperCanvas.qml available in your project
• Include js/paper-dom.js, js/paper-full.js, js/xmldom.js in your project. When loading these files, PaperCanvas searches for them in the main resource file of the application. In case the files are copied to another path, they can be configured as such:

PaperCanvas{
    id: paperCanvas
    width: 300
    height: 300
    xmldomPath: 'path/to/xmldom.js'
    domScriptPath: 'path/to/paper-dom.js'
    paperScriptPath: 'path/to/paper-full.js'
}

Implementation Info

Since qml's javascript engine does not properly support requiring javascript files, PaperQml uses the distributed paper-full.js file.

The js/paper-dom.js file provides minimal DOM functionality to make paperjs work.

PaperCanvas wraps a qml Canvas object, and loads both paper-dom and paper-full and emits the paperReady signal once both files have finished loading.

Limitations

Opacity and blend modes

In comparison to the html Canvas, the qml Canvas allows access to its context only during the onPaint handler:

Canvas{
    onPaint: {
        var ctx = getContext("2d");
        // use ctx ...
    }
}

This disables the application to create and work with multiple Canvases at the same time, as the application needs to wait for each Canvas to trigger the onPaint handler.

Paper.js uses this functionality in CanvasProvider, where it creates and reuses canvases for a number of reasons, including opacity and blending of items. Due to the above constraints, this implementation forces CanvasProvider to work with a single canvas, so features like opacity and blend modes will not work.

Speed

This implementation runs slightly slower than the browser alternative.