C++ Draggable Borderless Window Issue

3
votes

I'm designing a custom window border, and i put a bitmap on the top as a drag bar. This works, however when i try to drag the window, it places itself in two different areas and flickers between the two. Here's a video:

http://dl.dropbox.com/u/85700751/capture-1.avi

When the window is flashing, i'm trying to drag it (it doesn't show my cursor for some reason). Here's my dragging code:

case WM_LBUTTONDOWN: {
    int posX = LOWORD(lParam);
    int posY = HIWORD(lParam);
    if((isDragging==false)&&(posX>4)&&(posX<470)&&(posY>4)&&(posY<24))
        {
            isDragging = true;
            ClipCursor(rect);
            oldCursorX = posX;
            oldCursorY = posY;
        }
    }
    break;
case WM_LBUTTONUP: {
    isDragging = false;
    ClipCursor(NULL);
    }
    break;
case WM_MOUSEMOVE: {
        if(isDragging)  {
            SetWindowPos(hWnd, NULL, LOWORD(lParam)-oldCursorX, HIWORD(lParam)-oldCursorY, 500, 500, NULL);
        }
    }
    break;
2
c++winapivisual-studio-2012

2 Answers

5
votes

It's generally easiest to simply resond to WM_NCHITTEST. For that message, the LPARAM will have the mouse hit X and Y coordinates (same as WM_LBUTTONDOWN). If they're within your draggable area just return HTCAPTION. The system will then automatically handle all the drag logic for you.

0
votes

The cursor coordinates passed to WM_MOUSEMOVE are relative to the window position. But you keep changing the window position with every WM_MOUSEMOVE recieved.

Convert the coordinates to Screen coordinates using ::ClientToScreen().