javascript - QML Canvas - Why is the requestPaint() function not calling the paint? -


reproducible example:

here have drawn beizer curve qml canvas. paint gets called once though change start , end values explicitly causing signal generate.

see output too. why requestpaint() function doesn't call paint?

test.qml

import qtquick 2.4  canvas {     id: head; width: parent.width; height: parent.height      property int    curvestartx: -1     property int    curvestarty: -1     property int    curveendx: -1     property int    curveendy: -1      rectangle     {         id: startcontrolpoint         x:  head.curvestartx; y: head.curvestarty; width: 15; height: 15; color: "red"; radius: 100          onxchanged:           {             console.log("start called x1");             head.requestpaint();             console.log("start called x2")         }          onychanged:           {             console.log("start called y1");             head.requestpaint();             console.log("start called y2")         }     }      rectangle     {         id: endcontrolpoint         x: head.curveendx; y: head.curveendy; width: 15; height: 15; color: "red"; radius: 100         onxchanged:  head.requestpaint ()         onychanged:  head.requestpaint ()     }      onpaint:     {         console.log ("paint got called!")          var ctx = getcontext ("2d");         ctx.beginpath ();         ctx.clearrect (0, 0, head.height, head.width);         ctx.fill ();          ctx.strokestyle = head.curvecolor         ctx.linewidth   = 2;          ctx.beginpath ();         // start point of curve.         ctx.moveto (head.curvestartx, head.curvestarty)         ctx.beziercurveto (startcontrolpoint.x, startcontrolpoint.y,                            endcontrolpoint.x, endcontrolpoint.y,                            head.curveendx, head.curveendy);         ctx.stroke ();     } }

main.qml

import qtquick 2.4 import qtquick.window 2.2  window {     visible: true     height: 500     width: 500      test     {         id:     }      component.oncompleted:     {         what.curvestartx = 0         what.curvestarty = 0          what.curveendx = 50         what.curveendy = 50         /////////////////////////////////////////         what.curvestartx = 10         what.curvestarty = 10          what.curveendx = 60         what.curveendy = 60     } }

output:

qml debugging enabled. use in safe environment. qml: start called x1 qml: start called x2 qml: start called y1 qml: start called y2 qml: start called x1 qml: start called x2 qml: start called y1 qml: start called y2 qml: start called x1 qml: start called x2 qml: start called y1 qml: start called y2 qml: paint got called!

requestpaint() requests canvas repainted. if take qquickcanvasitem::requestpaint():

void qquickcanvasitem::requestpaint() {     markdirty(d_func()->canvaswindow); }

you can see calls qquickcanvasitem::markdirty():

void qquickcanvasitem::markdirty(const qrectf& rect) {     q_d(qquickcanvasitem);     if (!d->available)         return;      d->dirtyrect |= rect;      polish(); }

which in turn calls qquickitem::polish():

void qquickitem::polish() {     q_d(qquickitem);     if (!d->polishscheduled) {         d->polishscheduled = true;         if (d->window) {             qquickwindowprivate *p = qquickwindowprivate::get(d->window);             bool maybeupdate = p->itemstopolish.isempty();             p->itemstopolish.insert(this);             if (maybeupdate) d->window->maybeupdate();         }     } }

so paint() signal emitted whenever scenegraph decides ready. signal emitted in qquickcanvasitem::updatepolish().


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