Ali Parr Ali Parr - 3 years ago 95
C++ Question

How to fix an MFC Painting Glitch?

I'm trying to implement some drag and drop functionality for a material system being developed at my work. Part of this system includes a 'Material Library' which acts as a repository, divided into groups, of saved materials on the user's hard drive.

As part of some UI polish, I was hoping to implement a 'highlight' type feature. When dragging and dropping, windows that you can legally drop a material onto will very subtly change color to improve feedback to the user that this is a valid action.

I am changing the bar with 'Basic Materials' (Just a CWnd with a CStatic) from having a medium gray background when unhighlighed to a blue background when hovered over. It all works well, the OnDragEnter and OnDragExit messages seem robust and set a flag indicating the highlight status. Then in OnCtrlColor I do this:

if (!m_bHighlighted) {
pDC->FillSolidRect(0, 0, m_SizeX, kGroupHeaderHeight, kBackgroundColour);
else {
pDC->FillSolidRect(0, 0, m_SizeX, kGroupHeaderHeight, kHighlightedBackgroundColour);

However, as you can see in the screenshot, the painting 'glitches' below the dragged object, leaving the original gray in place. It looks really ugly and basically spoils the whole effect.

Is there any way I can get around this?

Answer Source

Thanks for the answers guys, ajryan, you seem to always come up with help for my questions so extra thanks.

Thankfully this time the answer was fairly straightforward....

m_pDragDropTargetWnd->SendMessage(WM_USER_DRAG_DROP_OBJECT_DRAG_ENTER, (WPARAM)pDragDropObject, (LPARAM)(&dragDropPoint));

This turns off the drawing of the dragged image, then sends a message to the window being entered to repaint in a highlighted state, then finally redraws the drag image over the top. Seems to have done the trick.

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