added auto fit wrapper function

src/diagram.typ

@@ -1,4 +1,4 @@
-#import "utils.typ": get-group-span
+#import "utils.typ": get-group-span, fit-canvas
 #import "renderer.typ": render
 #import "participant.typ" as participant: _par, PAR-SPECIALS
 
@@ -18,7 +18,7 @@
   ),)
 }
 
-#let diagram(elements) = {
+#let diagram(elements, width: auto) = {
   if elements == none {
     return
   }
@@ -188,7 +188,8 @@
   }
 
   set text(font: "Source Sans 3")
-  render(participants, elmts)
+  let canvas = render(participants, elmts)
+  fit-canvas(canvas, width: width)
 }
 
 #let from-plantuml(code) = {

src/utils.typ

@@ -40,4 +40,24 @@
   }
 
   panic("Invalid type for parameter mods, expected auto or dictionary, got " + str(type(mods)))
-}
+}
+
+#let fit-canvas(canvas, width: auto) = layout(size => {
+  let m = measure(canvas)
+  let w = m.width
+  let h = m.height
+  let r = if w == 0pt {0} else {
+    if width == auto {1} else {
+      size.width * width / w
+    }
+  }
+  let new-w = w * r
+  let new-h = h * r
+  r *= 100%
+  
+  box(
+    width: new-w,
+    height: new-h,
+    scale(x: r, y: r, reflow: true, canvas)
+  )
+})