Optimized Line drawing in QT -

i new qt. working on graphics.

i using qwidget drawing graphics(for drawing graphics in qwidget paint event). need draw background , foreground graphics. background fixed graphics. foregrounds drawing lines.

each 100 millisecond need draw 20points. drawing time 8 sec. total need draw 1600 points (total points represents contentious line).

i using qtimer invoke drawing in each 100ms. first few drawing drawn fast. in middle of drawing it's become slow.

the problem need draw foreground , background in each 100ms.

please me fix problem. if 1 have sample code please provide. in advance.

is there way draw partial area ie. particular modified region of graphics?

qpainter-drawing can slow without hardware support. using qgraphicsview won't if lines visible, since internally uses qpainter anyway.

if have draw 20 new points (or lines) per update , per update background gets cleared have render again, there few things try:

1) disable background autofill. see: qwidget::autofillbackground add widget init:

setautofillbackground(false); setattribute(qt::wa_opaquepaintevent, true); setattribute(qt::wa_nosystembackground, true); 

now on first update render background , first lines. next updates skip rendering background , render new lines.

2) use double buffering. example, create qimage of size of widget.

.h private:   qimage m_targetimage;   .cpp   // constructor     m_targetimage = qimage(width(), height(), qimage::format_argb32);     // paint event     // draw image    qpainter p;    p.begin(&m_targetimage);    static bool firstupdate = true;    if (firstupdate)    {      // draw background)     p.drawimage(...);     firstupdate = false;    }     // draw latest lines    p.drawlines(....);    p.end();     // draw image in widget paint    qpainter painter;    painter.begin(this);    painter.drawimage(0, 0, m_targetimage);    painter.end(); 

3) use qglwidget if possible. inherit widget qglwidget instead of qwidget. method doesn't work on platforms , speed increase might not enough. using opengl brings kind of new problems.