Question

I need to implement mouse drag events which look something like this:

class MouseDragEvent
{
public:
   uint m_btn;
   uint m_x, m_y;
   uint m_delta_x, m_delta_y;
};

I think I will need to check for WM_LBUTTONDOWN and WM_LBUTTONUP messages and manually find the change in x and y. Is there a drag message or a better way?

Answer 1

Start by detecting WM_LBUTTONDOWN. Record the starting coordinates where the mouse button was pressed. Check for WM_MOUSEMOVE, and when the mouse has moved outside the rectangle determined by GetSystemParameters(SM_CXDRAG) and GetSystemParameters(SM_CYDRAG) use SetCapture to capture the mouse. At this point continue responding to WM_MOUSEMOVE and check for WM_LBUTTONUP. You might want to change the mouse cursor at this point. Also check for WM_CAPTURECHANGED, which means the drag has been aborted. After the drag is complete call ReleaseCapture.

Edit: Most of this process can be automated with the DragDetect function. Call this function from the WM_LBUTTONDOWN handler.