Thread: redraw after minimize or change window size

Hi guys

I have next problems
I have base class "Shape", it cointains virtual function draw(HWND), I have child class "Line" which contains same function draw(hwnd).
When I draw line in WM_MOUSEMOVE, it is all ok, but when I minimize or change window size, my line disappear
I have vector with pointer to base class

Code:

vector<Shape*>ff;
Shape *f;

 case WM_LBUTTONDOWN:
    {

        IsDrawing = TRUE;

        StartX = LOWORD(lParam);
        StartY = HIWORD(lParam);
        EndX = LOWORD(lParam);
        EndY = HIWORD(lParam);

        switch(iShape)
        {
        case LINE:
                f=new Line();
            break;
        case  RECTANGLE:
            f=new MyRectangle();
            break;
        }

        f->SetBrushWidth(5);
        f->SetColor(RGB(255,0,0));
        f->SetStartCoord(StartX,StartY);
        f->SetEndCoord(EndX,EndY);
        f->SetMode(1);
        f->draw(hWnd);
        break;
    }

  case WM_MOUSEMOVE:
    if( IsDrawing == TRUE )
    {
        f->SetEndCoord(EndX,EndY);
        f->SetMode(2);
        f->draw(hWnd);
        EndX = LOWORD(lParam);
        EndY = HIWORD(lParam);
        f->SetEndCoord(EndX,EndY);
        f->SetMode(2);
        f->draw(hWnd);
    }

    break;

case WM_LBUTTONUP:


    EndX = LOWORD(lParam);
    EndY = HIWORD(lParam);

    f->SetEndCoord(EndX,EndY);
    f->SetMode(3);
    f->draw(hWnd);
    ff.push_back(f);

    IsDrawing = FALSE;
 break;

It is drawing ok, but when change windows size
What I do wrong?

You need to do your drawing in the WM_PAINT message handler.

Originally Posted by DaveH

You need to do your drawing in the WM_PAINT message handler.

This works well when there is no interactive user drawing or interactive text output. Reading in some data and then
drawing a graph is a good example. All drawing is done in the WM_PAINT message handler. The program does the
initial drawing by calling InvalidateRect() for the client area to be drawn. A call to UpdateWindow() might also be needed
if the WM_PAINT message, will will be subsequently sent, needs to have more priority.

Nothing else needs to be done to maintain the drawing in the window in this case. The OS will send WM_PAINT messages
as necessary, and the WM_PAINT message handler will redraw the window. Obviously, the entire drawing procedure needs
to be within the WM_PAINT message handler.

So this would not work well with an interactive drawing program.

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