[add] possibility to specify negative values for gate groups, so that their end counts from the back/bottom.

Closes  #36

Author: Mc-Zen

src/decorations.typ

@@ -232,11 +232,11 @@
 /// them. 
 #let gategroup(
 
-  /// Number of wires to include.
+  /// Number of wires to include. If negative, the end is counted from the back. 
   /// -> int
   wires, 
 
-  /// Number of columns to include.
+  /// Number of columns to include. If negative, the end is counted from the bottom. 
   /// -> int
   steps, 
 

src/quantum-circuit.typ

@@ -365,6 +365,12 @@
     for (item, x, y) in meta-instructions {
       let (the-content, decoration-bounds) = (none, none)
       if item.qc-instr == "gategroup" {
+        if item.steps < 0 {
+          item.steps = num-cols - x + item.steps + 1
+        }
+        if item.wires < 0 {
+          item.wires = num-rows - y + item.wires + 1
+        }
         verifications.verify-gategroup(item, x, y, num-rows, num-cols)
         let (dy1, dy2) = layout.get-cell-coords(center-y-coords, row-heights, (y, y + item.wires - 1e-9))
         let (dx1, dx2) = layout.get-cell-coords(center-x-coords, col-widths, (x, x + item.steps - 1e-9))

tests/decorations/gategroup/ref/2.png

@@ -5,4 +5,14 @@
   gategroup(1, 2, label: ((pos: top, content: "A"), (pos: left, content: "B")),), $K$, 1, 5pt, swap(), [\ ],
   2, swap(-1), 
   gategroup(2, 1, x: 2, y: 0, label: "swap", stroke: .5pt + blue, radius: 4pt, fill: blue)
+)
+
+#pagebreak()
+
+
+#quantum-circuit(
+  gategroup(1, -1), $X$, $Y$, $p$, [\ ],
+  gategroup(-1, -2), $X$, $Y$, $p$, [\ ],
+  [\ ],
+  gategroup(x: 2, y: 1, -2, 1)
 )