Simple QGraphicsTextItem animation (pos or blurRadius) is not smooth.

Diracsbracket

Hello,
I'm am trying out a simple text animation using the QGraphicsView framework, using the code shown below to scroll the text vertically in and back out of the view.
However, the movement e.g. with the linear easing curve is not fluid as there seem to be transition discontinuities at certain times.

How can I prevent this?

MainWindow::MainWindow(QWidget *parent) :
    QMainWindow(parent),
    ui(new Ui::MainWindow)
{
    ui->setupUi(this);
    QGraphicsScene* scene;

    scene = new QGraphicsScene(this);
    scene->setSceneRect(ui->graphicsView->rect());

    ui->graphicsView->setScene(scene);
    //ui->graphicsView->setRenderHint(QPainter::Antialiasing, true);

    m_text = scene->addText("Hello World", QFont("Arial", 20));
    m_text->setScale(4.0);

    qreal h = m_text->boundingRect().height()*m_text->scale();

    m_text->setPos(0, -h);
    m_anim = new QPropertyAnimation(m_text, "y" , this);
    m_anim->setDuration(2000);
    m_anim->setStartValue(-h);
    m_anim->setEndValue(ui->graphicsView->height());
    m_anim->setEasingCurve(QEasingCurve::Linear);
}

void MainWindow::on_pushButton_clicked()
{
    m_anim->start();
}

Diracsbracket

With a blur graphics effect, the result is even worse. When animating the blurRadius property from 100 to 0, the last part of the animation is completely unstable, as the gif animation below shows
(the higher frame-rate GIF is too big to upload here, but shows the effect as even worse).

Asperamanca

My first approach would be to dump the values set during the property animation.
Any reason you commented the line that enables antialiasing? That could at least explain part of the text movement being irregular.

Diracsbracket

@Asperamanca said in Simple QGraphicsTextItem animation (pos or blurRadius) is not smooth.:

Any reason you commented the line that enables antialiasing

Hey, thanks for your reply. I commented that one as a test. I tried both with antialiasing enabled and disabled.

Asperamanca

I've tested your example and dumped the property animation output. The numbers really are irregular, although I do not know whether this sufficiently explains the visible effect. It may also be related to this bug report: https://bugreports.qt.io/browse/QTBUG-4416

Absolute value   Relative to previous value
-204	
-202,245	-1,755
-200,373	-1,872
-198,501	-1,872
-196,629	-1,872
-194,757	-1,872
-192,885	-1,872
-191,013	-1,872
-189,141	-1,872
-187,269	-1,872
-185,397	-1,872
-183,525	-1,872
-181,653	-1,872
-179,781	-1,872
-177,909	-1,872
-176,037	-1,872
-174,165	-1,872
-172,293	-1,872
-170,304	-1,989
-168,549	-1,755
-166,677	-1,872
-164,805	-1,872
-162,933	-1,872
-161,061	-1,872
-159,189	-1,872
-157,317	-1,872
-155,328	-1,989
-153,573	-1,755
-151,701	-1,872
-149,829	-1,872
-147,957	-1,872
-146,085	-1,872
-144,213	-1,872
-142,341	-1,872
-140,469	-1,872
-138,48	-1,989
-136,725	-1,755
-134,853	-1,872
-132,981	-1,872
-131,109	-1,872
-129,237	-1,872
-127,365	-1,872
-125,493	-1,872
-123,621	-1,872
-121,749	-1,872
-119,877	-1,872
-118,005	-1,872
-116,133	-1,872
-114,261	-1,872
-112,389	-1,872
-110,517	-1,872
-108,645	-1,872
-106,773	-1,872
-104,901	-1,872
-103,029	-1,872
-101,157	-1,872
-99,168	-1,989
-97,413	-1,755
-95,541	-1,872
-93,669	-1,872
-91,797	-1,872
-89,925	-1,872
-88,053	-1,872
-86,181	-1,872
-84,309	-1,872
-82,437	-1,872
-80,565	-1,872
-78,576	-1,989
-76,821	-1,755
-74,832	-1,989
-73,077	-1,755
-71,088	-1,989
-69,333	-1,755
-67,461	-1,872
-65,589	-1,872
-63,717	-1,872
-61,845	-1,872
-59,973	-1,872
-58,101	-1,872
-56,229	-1,872
-54,357	-1,872
-52,485	-1,872
-50,613	-1,872
-48,741	-1,872
-46,869	-1,872
-44,997	-1,872
-43,125	-1,872
-41,253	-1,872
-39,381	-1,872
-37,509	-1,872
-35,637	-1,872
-33,765	-1,872
-31,776	-1,989
-30,021	-1,755
-28,149	-1,872
-26,16	-1,989
-24,288	-1,872
-22,533	-1,755
-20,661	-1,872
-18,789	-1,872
-16,917	-1,872
-15,045	-1,872
-13,173	-1,872
-11,301	-1,872
-9,429	-1,872
-7,557	-1,872
-5,685	-1,872
-3,813	-1,872
-1,941	-1,872
-0,069	-1,872
1,803	-1,872
3,675	-1,872
5,547	-1,872
7,419	-1,872
9,291	-1,872
11,163	-1,872
13,035	-1,872
15,024	-1,989
16,779	-1,755
18,651	-1,872
20,523	-1,872
22,512	-1,989
24,267	-1,755
26,139	-1,872
28,011	-1,872
29,883	-1,872
30	-0,117

Diracsbracket

@Asperamanca
Thanks for taking the time to try my example and investigate it, and sorry for not reacting sooner. I have completed my simple scrolling text widget which fades in and out using a transparency gradient, and although not perfectly smooth, I didn't have the time to investigate the issue further, but I'll post any findings that I may find later here. Cheers~