Need help on drawling line in OnPaint function

[John502]

Hi, I am able to draw vertical line on dialog, line will move from left to right for the period of time. while moving i am erasing the previous line with previous pixels and drawing new line with new pixels... but while the line is moving, if i have opened any other application on dialog box, the prevois line is not erasing and it is continue with the new line.. can any one help me why it is happening like this...? Thanks in advance.. Any advice will be appriciated..

[Cedric Moonen]

What are you doing exactly in the OnPaint handler ? What you have to think is that windows doesn't remember the drawings for your window. So it means that whenever it needs to repaint the window (for instance because you have another window on top), then it will ask your window to repaint itself (by sending a WM_PAINT message). If you don't redraw your window properly, then you will loose some data. Also, the ebest way to erase a previous line your example is to simply request a new repainting of your window and draw the line at the new position (as everything is cleared, your previous line won't be visible anymore).

Cédric Moonen Software developer
Charting control [v1.5] OpenGL game tutorial in C++

[John502]

Hi cedric, Thanks for your reply.. actually i am drawing line along with the slider positions on dialog, i mean slider will move from left to right, that time along with slider positions the line will also move. I have written the below code in one thread.. m_pDlg->GetClientRect( &deflatedClientRect ); deflatedClientRect.DeflateRect( TB_WIDTH, TB_WIDTH ); m_pDlg->m_slider_bar1.SetPos(slide_pos); m_pDlg->m_slider_bar2.SetPos(slide_pos); m_pDlg->m_slider_bar1.GetThumbRect( &thumbRect ); m_pDlg->m_slider_bar1.ClientToScreen( &thumbRect ); m_pDlg->ScreenToClient( &thumbRect ); ptStart.x = thumbRect.CenterPoint().x; ptStart.y = TB_WIDTH; //ptEnd.x = ptStart.x; //ptEnd.y = deflatedClientRect.bottom; m_pDlg->x1 = ptStart.x; m_pDlg->x2 = ptStart.x; //m_pDlg->x2 = ptEnd.x; //m_pDlg->y2 = 280; m_pDlg->InvalidateRect(deflatedClientRect,TRUE); using this code i will get sliders pixels information, and i am calling InavalidateRect from here. In Onpaint i am using below code snippet.. int nOldmode=dc.SetROP2(R2_NOTXORPEN); dc.MoveTo(old_x1,old_y1); dc.LineTo(old_x2,old_y2); dc.MoveTo(x1,y1); dc.LineTo(x2,y2); old_x1 = x1; old_y1 = y1; old_x2 = x2; old_y2 = y2; plase check the code and let me know that is the problem..> thnaks in advance..

[Cedric Moonen]

Did you read my previous message ? Why are you repainting the old line ?

venki502 wrote:

I have written the below code in one thread..

You are doing that in a separate thread ? :wtf: I wouldn't do that: instead simply handle the slider moved event and update the position of your line at that point. Why do you need a thread for that ?

Cédric Moonen Software developer
Charting control [v1.5] OpenGL game tutorial in C++

[John502]

Hi, Actualli i am setting the slider position in OnTimer function, Okay can you please tell me the event fired at silder movement, so that i will try with that.. Thanks.

[Iain Clarke Warrior Programmer]

This is getting painful to read. 1/ In your thumbtrack handler, just call InvalidateRect () to cause the window to redraw. 2/ In the OnPaint routine, get the thumb positions, calculate your two end points for the line. Draw the line. Go home and sleep. It's not a complex problem. I have no idea why you're bringing in threads, etc. If you want, you could be clever and use R2_NOT to undraw a line, and draw it in the new position, but that seems a little over complex at the moment. Good luck, Iain.

Codeproject MVP for C++, I can't believe it's for my lounge posts...