Add documentation for 'withViewBox'.

Former-commit-id: 2797121d09679950ac35b1bd08e9c6bfbedc5267

docs/gen_doc_gifs.sh

@@ -5,6 +5,8 @@ TINY='^(doc_turbo|doc_viridis|doc_magma|doc_inferno|doc_plasma|doc_sinebow|doc_c
         newline|doc_hsvMatlab|doc_greyscale|doc_parula|doc_rgbComponents|doc_hsvComponents|
         newline|doc_hsv|doc_lchComponents|doc_xyzComponents|doc_labComponents)$'
 
+SQUARE='^(doc_withViewBox)$'
+
 cd $ROOT/examples/
 for src in $ROOT/examples/doc_*.hs; do
   BASE=`basename $src .hs`
@@ -13,6 +15,9 @@ for src in $ROOT/examples/doc_*.hs; do
     if [[ "$BASE" =~ $TINY ]]; then
       echo "stack $src render -o $DST --width=320 --height=50"
       stack $src render -o $DST --width=320 --height=50
+    elif [[ "$BASE" =~ $SQUARE ]]; then
+      echo "stack $src render -o $DST --width=180 --height=180"
+      stack $src render -o $DST --width=180 --height=180
     else
       echo "stack $src render -o $DST"
       stack $src render -o $DST

examples/doc_withViewBox.hs

@@ -0,0 +1,10 @@
+#!/usr/bin/env stack
+-- stack runghc --package reanimate
+{-# LANGUAGE OverloadedStrings #-}
+module Main (main) where
+
+import           Reanimate
+
+main :: IO ()
+main = reanimate $ animate $ const $
+  withViewBox (0,0,1,1) $ mkBackground "yellow"

src/Reanimate/Svg/Constructors.hs

@@ -375,6 +375,12 @@ mkText str =
 --   to configure them by hand.
 --
 --   The viewbox argument is (min-x, min-y, width, height).
+--
+--   Example:
+--
+--   > withViewBox (-4,-4,8,8) $ mkBackground "yellow"
+--
+--   <<docs/gifs/doc_withViewBox.gif>>
 withViewBox :: (Double, Double, Double, Double) -> Tree -> Tree
 withViewBox vbox child = translate (-screenWidth/2) (-screenHeight/2) $
   SvgTree $ Document