Splitting Gridlines - Shape Insertion

4.2 Shape Insertion

4.2.6 Splitting Gridlines

Figure 4.7a shows how the user may insert a table column between the two existing ones. The desired outcome is shown in Fig. 4.7b. If the snapping algorithm Alg. 2 computed extremal gridline locations gl_l = (l, G_l), gl_r = (r, G_r) with l = r, depending on the direction d computed by the same algorithm, all source gridlines will have been inserted at positionsl−i, i≥0 if d = low or at l+i, i ≥0 otherwise. The situation for d = high is shown in Fig. 4.8. The two rectanglesA and B are adjacent. They are both bound to gridline g between them. The new rectangleC has been inserted directly on gridline g, i.e., l = r = g.v, g ∈ G_l and g ∈ G_r. Because d = high, the gridlines of rectangleChave been inserted right ofg. Gridlineg_i in the figure is the rightmost gridline of C and its location is g.v+i.

The algorithm collects the set of gridlinesG, bound to the inserted shapes S, the left-most gridline if d=low or the right-most gridline if d=high. In the example of Fig. 4.8a, since d = high, G := {g_i}. G thus contains the right-most newly inserted gridlines with position g.v +i. All gridlines in

CONTRA PRO

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(a) (b)

Figure 4.7: Snapping the column on the gridline between two columns inserts the column, thus splitting the gridline.

A B

Figure 4.8: Separating adjacent shapes to insert a shape on a gridline.

4.2. SHAPE INSERTION 67 Algorithm 6: MergeGridlines algorithm

Input: A set of gridlines G6=∅ such that ∀g, g⁰ ∈G:g.v =g⁰.v Output: A single merged gridlinegM

1 begin

2 g_M ←g ∈G

3 G←G\{g}

4 foreach g ∈G do

5 if g.f then

6 gM.f ←true

7 end

8 foreach s∈ S do

9 if g ∈s.Gx/y then

10 replace g with g_M ins.G_x/y

11 end

12 end

13 end

14 end

G are merged to a single gridline g_M. Interval set I is set to the interval of extremal values of the span of gM, i.e., I spans the entire height of shapeC.

In the example, it follows that g_M =g_i.

In the following, every shapes∈ S\Sthat is attached to a gridlinegl∈Gl

is considered. For each shape,I_s is set to the spans covers ong_l in direction d. In the example above, both A and B are attached to gridline g. Because d = high, Is is the span on the right of g. This span is empty for shape A because it touchesg from the left. I_s contains a single interval for shape B.

Now,I is the span ofg_M, i.e., of the new gridline that is squeezed between A andB. I_s is the span ofB at its original position. BecauseI∩I_s6=∅, the left side ofB should be pushed rightwards tog_M. Intuitively, this means that if C were inserted with zero width at gridline g and then slowly widened, shapes C and B would collide and shape C should push B rightwards as shown in Fig. 4.8b.

Alternatively, if C were smaller, the situation of Fig. 4.9 may arise were I ∩I_s 6= ∅ and I ⊂ I_s. In this case, shape B is not moved but everything is left as is. As a result, shape C is inserted to the right of g as before but inside B.

Algorithm 7: SplitGridline

Input: Inserted shapes S, gridline location gl_l(l, G_l), insertion direction d

1 begin

2 G← ∅

3 if d=lowthen

4 G← {g |g.v = min_g_i∈s.G_x/y,s∈S(g_i.v)}

5 else

6 G← {g |g.v = max_g_i∈s.G_x/y,s∈S(g_i.v)}

7 end

8 g_M ←MergeGridlines(G)

9 I ←^Sspan(gM, d=low ? high:low)

10 if I 6=∅ then

11 I ← {(min_(a⁰_,b⁰)∈I(a⁰),max_(a⁰_,b⁰)∈I(b⁰))}

12 foreach g_l ∈G_l∧ ¬g_l.f do

13 foreach s∈ S\S such that g_l∈s.G_x/y do

14 I_s←s.span_x/y(g_l, d)

15 if Is∩I 6=∅ ∧I 6⊂Is then

16 replaceg_l with g_M ins.G_x/y

17 end

18 end

19 end

20 end

21 end

Im Dokument Sketching Slides (Seite 77-80)