Mouse click dragging: surprising click positions?

[unpacklo]

Hey Omar,

I've been working on a feature that required me to detect when the mouse was clicked and subsequently dragged. I wrote a small code sequence to help me detect this case:

    static bool leftPressed = false, leftReleased = false, leftPrev = false, isDragging = false;
    static int dragCount = 0;
    ImGuiIO *io = &ImGui::GetIO();
    leftPressed = !leftPrev && io->MouseDown[0];
    leftReleased = leftPrev && !io->MouseDown[0];
    leftPrev = io->MouseDown[0];

    if (leftReleased)
    {
        printf("Left released!\n");
        isDragging = false;
    }

    const float DRAG_RADIUS = 4.0f;
    ImVec2 distFromClick(io->MouseClickedPos[0]);
    distFromClick -= ImGui::GetMousePos();

    if (!isDragging && io->MouseDown[0] && (((distFromClick.x * distFromClick.x) + (distFromClick.y * distFromClick.y)) > (DRAG_RADIUS * DRAG_RADIUS)))
    {
        printf("Started dragging!\n");
        isDragging = true;
    }

    if (isDragging)
    {
        printf("Dragging %d\n", ++dragCount);
    }

The issue I ran into was that this can detect double clicking as a drag if the mouse is moved quickly between each click (so that the drag threshold is exceeded).

I took a look at the code that sets the click positions

imgui/imgui.cpp

Lines 1829 to 1839 in ff5378b

	if (g.Time - g.IO.MouseClickedTime[i] < g.IO.MouseDoubleClickTime)
	{
	if (ImLengthSqr(g.IO.MousePos - g.IO.MouseClickedPos[i]) < g.IO.MouseDoubleClickMaxDist * g.IO.MouseDoubleClickMaxDist)
	g.IO.MouseDoubleClicked[i] = true;
	g.IO.MouseClickedTime[i] = -FLT_MAX; // so the third click isn't turned into a double-click
	}
	else
	{
	g.IO.MouseClickedTime[i] = g.Time;
	g.IO.MouseClickedPos[i] = g.IO.MousePos;
	}

and was wondering if there is a reason why the click position is not updated during the double click time? Updating the click positions on every click, regardless of whether or not its in the double click time, makes more sense to me.

For now, I work around this issue by keeping track of the click positions on my own.

-Dale Kim

[ocornut]

Looking into it. Allow refer to the ImGui::GetItemActiveDragDelta() function which gives you the dragging delta for a given widget (and that widget can be an invisible button as well).

[ocornut]

Was just a bug. Fixed!

[ocornut]

I have replaced GetItemActiveDragDelta() which was added a day or two ago with a more consistent and useful dragging API

bool          IsMouseDragging(int button = 0, float lock_threshold = -1.0f);
ImVec2        GetMouseDragDelta(int button = 0, float lock_threshold = -1.0f);

lock_threshold < 0.0f uses the default in io.MouseDragThreshold (6.0f by default)
You can override it if you need a widget that doesn't have a threshold. The data are stored in a way that you can query it using different threshold.