Invalid hover detection when windows are touching

[luknw]

What?

When windows are pixel-perfect aligned one next to the other, the hover status isn't updated properly.

Minimum example

Replace the window in the default demo with the following:

if (nk_begin(ctx, "Demo1", nk_rect(100, 100, 200, 200),
    NK_WINDOW_MOVABLE|NK_WINDOW_CLOSABLE|NK_WINDOW_MINIMIZABLE|NK_WINDOW_TITLE))
{
    nk_layout_row_dynamic(ctx, 80, 1);
    nk_button_label(ctx, "button");
}
nk_end(ctx);
if (nk_begin(ctx, "Demo2", nk_rect(300, 100, 200, 200),
    NK_WINDOW_MOVABLE|NK_WINDOW_CLOSABLE|NK_WINDOW_MINIMIZABLE|NK_WINDOW_TITLE))
{
    nk_layout_row_dynamic(ctx, 80, 1);
    nk_button_label(ctx, "button");
}
nk_end(ctx);

The left button doesn't react on hover.

When windows are spread apart by 1 or more pixels, hover works fine:

if (nk_begin(ctx, "Demo1", nk_rect(100, 100, 200, 200),
    NK_WINDOW_MOVABLE|NK_WINDOW_TITLE))
{
    nk_layout_row_dynamic(ctx, 80, 1);
    nk_button_label(ctx, "button");
}
nk_end(ctx);
if (nk_begin(ctx, "Demo2", nk_rect(300 + 1, 100, 200, 200),
    NK_WINDOW_MOVABLE|NK_WINDOW_TITLE))
{
    nk_layout_row_dynamic(ctx, 80, 1);
    nk_button_label(ctx, "button");
}
nk_end(ctx);

Suggested fix

The hover isn't updated, because windows are detected as intersecting each other:

Nuklear/src/nuklear_window.c

Lines 221 to 242 in adc52d7

	/* activate window if hovered and no other window is overlapping this window */
	inpanel = nk_input_has_mouse_click_down_in_rect(&ctx->input, NK_BUTTON_LEFT, win_bounds, nk_true);
	inpanel = inpanel && ctx->input.mouse.buttons[NK_BUTTON_LEFT].clicked;
	ishovered = nk_input_is_mouse_hovering_rect(&ctx->input, win_bounds);
	if ((win != ctx->active) && ishovered && !ctx->input.mouse.buttons[NK_BUTTON_LEFT].down) {
	iter = win->next;
	while (iter) {
	struct nk_rect iter_bounds = (!(iter->flags & NK_WINDOW_MINIMIZED))?
	iter->bounds: nk_rect(iter->bounds.x, iter->bounds.y, iter->bounds.w, h);
	if (NK_INTERSECT(win_bounds.x, win_bounds.y, win_bounds.w, win_bounds.h,
	iter_bounds.x, iter_bounds.y, iter_bounds.w, iter_bounds.h) &&
	(!(iter->flags & NK_WINDOW_HIDDEN)))
	break;
	if (iter->popup.win && iter->popup.active && !(iter->flags & NK_WINDOW_HIDDEN) &&
	NK_INTERSECT(win->bounds.x, win_bounds.y, win_bounds.w, win_bounds.h,
	iter->popup.win->bounds.x, iter->popup.win->bounds.y,
	iter->popup.win->bounds.w, iter->popup.win->bounds.h))
	break;
	iter = iter->next;
	}
	}

The NK_INTERSECT is defined as:

Nuklear/src/nuklear.h

Lines 5405 to 5406 in adc52d7

	#define NK_INTERSECT(x0, y0, w0, h0, x1, y1, w1, h1) \
	(!(((x1 > (x0 + w0)) || ((x1 + w1) < x0) || (y1 > (y0 + h0)) || (y1 + h1) < y0)))

I'd suggest to fix the off-by-one error by making the upper bound exclusive:

#define NK_INTERSECT(x0, y0, w0, h0, x1, y1, w1, h1) \
    (!(((x1 >= (x0 + w0)) || ((x1 + w1) <= x0) || (y1 >= (y0 + h0)) || (y1 + h1) <= y0)))

This way, it would match all the other checks based on NK_BETWEEN which is also exclusive in the upper bound:

Nuklear/src/nuklear.h

Lines 5402 to 5404 in adc52d7

	#define NK_BETWEEN(x, a, b) ((a) <= (x) && (x) < (b))
	#define NK_INBOX(px, py, x, y, w, h)\
	(NK_BETWEEN(px,x,x+w) && NK_BETWEEN(py,y,y+h))