PicoVector: Avoid MicroPython GC.

Since we're not using tracked allocation, any memory we don't explicitly
hold a reference to will be assumed unused by MicroPython's GC.

Pass up the pp_nodes and pp_node_counts points (hackily) to fix this.

libraries/pico_vector/pico_vector.hpp

@@ -31,6 +31,10 @@ namespace pimoroni {
     class PicoVector {
         private:
             af_text_metrics_t text_metrics;
+            // Hold copies of pretty-poly's pointers
+            // so MicroPython does not garbage collect them!
+            void *_pp_nodes;
+            void *_pp_node_counts;
 
         public:
             static PicoGraphics *graphics;
@@ -40,6 +44,8 @@ namespace pimoroni {
                 // TODO: Make these configurable?
                 // Tile buffer size, Max nodes per scanline
                 pp_init(16);
+                _pp_nodes = pp_nodes;
+                _pp_node_counts = pp_node_counts;
 
                 pp_tile_callback(PicoVector::tile_callback);
 

libraries/pico_vector/pretty-poly.h

@@ -127,6 +127,11 @@ extern pp_tile_callback_t  _pp_tile_callback;
 extern pp_antialias_t      _pp_antialias;
 extern pp_mat3_t          *_pp_transform;
 
+// Our parent scope might want to hold a pointer to these
+// ie: MicroPython to avoid garbage collection
+extern int32_t *pp_nodes;
+extern uint32_t *pp_node_counts;
+
 void pp_clip(int32_t x, int32_t y, int32_t w, int32_t h);
 void pp_tile_callback(pp_tile_callback_t callback);
 void pp_antialias(pp_antialias_t antialias);