Add canvas-local bendin and zoom flags.

This adds canvas member variables and corresponding options for the declare object, so that the global (user) zoom and legacy bendin flags can be enabled and disabled separately for each canvas.

This was proposed (and deferred) earlier in !561 (closed) (which see for the previous discussion and rationale), but the original branch seems to be gone, so I've rebased it on the current master and pushed it again.

Jonathan, I really hate to revive this old MR which we discussed at length already. But we're 6 months on, we don't have author-centric zoom yet, and I'm still facing the same issue that prompted me to create this MR in the first place. As long as we don't have author-centric zoom yet, can we at least implement this as a stop-gap solution, please?

pd/doc/5.reference/declare-help.pd

-#N canvas 426 36 555 619 10;
-#X declare;
+#N canvas 424 39 559 621 10;
 #X declare;
+#X declare -path mylibs;
+#X declare -lib mylib;
+#X declare -bendin 1;
+#X declare -zoom 1;
+#X declare -stdpath mylibs;
+#X declare -stdlib mylib;
 #X obj 0 595 cnv 15 552 21 empty \$0-pddp.cnv.footer empty 20 12 0
-14 -228856 -66577 0;
+14 #dcdcdc #404040 0;
 #X obj 0 0 cnv 15 552 40 empty \$0-pddp.cnv.header declare 3 12 0 18
--204280 -1 0;
+#c4dcdc #000000 0;
 #X obj 0 105 cnv 3 550 3 empty \$0-pddp.cnv.inlets inlets 8 12 0 13
--228856 -1 0;
+#dcdcdc #000000 0;
 #N canvas 483 286 494 344 META 0;
 #X text 12 65 LIBRARY internal;
 #X text 12 105 WEBSITE http://crca.ucsd.edu/~msp/;
@@ -20,15 +25,15 @@ Wilkes revised the patch to conform to the PDDP template for Pd version
 #X text 12 5 KEYWORDS control pd_op;
 #X restore 500 597 pd META;
 #X obj 0 134 cnv 3 550 3 empty \$0-pddp.cnv.outlets outlets 8 12 0
-13 -228856 -1 0;
+13 #dcdcdc #000000 0;
 #X obj 0 164 cnv 3 550 3 empty \$0-pddp.cnv.argument arguments 8 12
-0 13 -228856 -1 0;
+0 13 #dcdcdc #000000 0;
 #X obj 0 386 cnv 3 550 3 empty \$0-pddp.cnv.more_info more_info 8 12
-0 13 -228856 -1 0;
+0 13 #dcdcdc #000000 0;
 #N canvas 215 523 428 103 Related_objects 0;
 #X obj 15 34 import;
 #X obj 1 1 cnv 15 425 20 empty \$0-pddp.cnv.subheading empty 3 12 0
-14 -204280 -1 0;
+14 #c4dcdc #000000 0;
 #X text 7 1 [declare] Related Objects;
 #X restore 101 597 pd Related_objects;
 #X obj 494 12 declare;
@@ -53,7 +58,6 @@ calling patch as well as the abstraction.);
 #X text 98 561 BUG: The name "-stdpath" is confusing \, as it has a
 quite different effect from "-stdpath" on the pd command line.;
 #X text 11 23 set environment for loading patch;
-#X text 139 69 NEEDS AN EXAMPLE;
 #X text 165 185 - the [declare] object adds one or more directories
 to the search path \, and/or pre-loads one or more libraries ("extensions")
 to Pd in preparation for opening the patch from a file. Usage is "declare
@@ -66,3 +70,39 @@ you can get it using "declare -stdpath extra/zexy".;
 #X text 80 185 n) symbol atom;
 #X obj 4 597 pddp/pddplink all_about_help_patches.pd -text Usage Guide
 ;
+#X obj 40 52 declare -path mylibs;
+#X obj 240 52 declare -lib mylib;
+#N canvas 480 186 444 475 Patch_local 0;
+#X obj 1 1 cnv 15 437 20 empty \$0-pddp.cnv.subheading empty 3 12 0
+14 #c4dcdc #000000 0;
+#X text 7 1 [declare] Patch-local options;
+#X obj 8 34 declare -bendin 1;
+#X text 131 34 enforces legacy (vanilla-compatible) bendin range;
+#X obj 8 62 declare -zoom 1;
+#X text 131 62 turns on load/restore of zoom levels in a patch;
+#X text 7 95 [declare] also offers some special (and experimental)
+patch-local options which override the corresponding global flags in
+the current patch (including all its one-off subpatches):, f 69;
+#X text 7 197 * [declare -zoom 0/1] turns save/restore of zoom levels
+on or off. This overrides the corresponding global option in the GUI
+preferences. Please note that this does *not* actually set the zoom
+level itself \, it merely enables or disables storing and retrieving
+that setting in a patch., f 69;
+#X text 7 277 CAVEATS: These options are only available in Purr Data
+at this time \, they are NOT supported by vanilla Pd (which has no
+way of configuring the bendin or zoom behavior)., f 69;
+#X text 7 327 The -zoom option is intended mainly for classroom use
+\, e.g. \, when projecting patches on a whiteboard. It ensures that
+the patch is displayed at the preset zoom level by default \, even
+if the global zoom save/load option is disabled in the preferences.
+If you abuse this option to enforce unusually high or low zoom levels
+\, you take away precious zoom levels from the user \, which is a VERY
+bad practice. So please use this option with due skill \, care \, and
+diligence \, or better don't use it at all., f 69;
+#X text 7 145 * [declare -bendin 0/1] turns the legacy bendin behavior
+on or off. This overrides the global -legacy-bendin command line option
+in a patch. Please see the bendin-help patch for further details.,
+f 69;
+#X restore 221 597 pd Patch_local;
+#X obj 40 76 declare -stdpath mylibs;
+#X obj 240 76 declare -stdlib mylib;