PicoVector: Improve transform handling.

* Store a reference to transform, so `set_transform(Transform())` is not GC'd until it is replaced
* Transformations return the transform, allowing chaining: `transform.rotate().scale().translate()`
* A new `get_transform` method for getting the currently set transform.

micropython/modules/picovector/picovector.c

@@ -96,6 +96,7 @@ static MP_DEFINE_CONST_FUN_OBJ_2(VECTOR_set_font_align_obj, VECTOR_set_font_alig
 static MP_DEFINE_CONST_FUN_OBJ_2(VECTOR_set_antialiasing_obj, VECTOR_set_antialiasing);
 static MP_DEFINE_CONST_FUN_OBJ_2(VECTOR_set_transform_obj, VECTOR_set_transform);
 static MP_DEFINE_CONST_FUN_OBJ_2(VECTOR_set_clip_obj, VECTOR_set_clip);
+static MP_DEFINE_CONST_FUN_OBJ_1(VECTOR_get_transform_obj, VECTOR_get_transform);
 
 static MP_DEFINE_CONST_FUN_OBJ_2(VECTOR_draw_obj, VECTOR_draw);
 
@@ -112,6 +113,7 @@ static const mp_rom_map_elem_t VECTOR_locals_dict_table[] = {
     { MP_ROM_QSTR(MP_QSTR_set_antialiasing), MP_ROM_PTR(&VECTOR_set_antialiasing_obj) },
     { MP_ROM_QSTR(MP_QSTR_set_transform), MP_ROM_PTR(&VECTOR_set_transform_obj) },
     { MP_ROM_QSTR(MP_QSTR_set_clip), MP_ROM_PTR(&VECTOR_set_clip_obj) },
+    { MP_ROM_QSTR(MP_QSTR_get_transform), MP_ROM_PTR(&VECTOR_get_transform_obj) },
 
     { MP_ROM_QSTR(MP_QSTR_draw), MP_ROM_PTR(&VECTOR_draw_obj) },
 };

micropython/modules/picovector/picovector.cpp

@@ -23,16 +23,17 @@ typedef struct _ModPicoGraphics_obj_t {
     bool blocking = true;
 } ModPicoGraphics_obj_t;
 
-typedef struct _VECTOR_obj_t {
-    mp_obj_base_t base;
-    PicoVector *vector;
-} _VECTOR_obj_t;
-
 typedef struct _TRANSFORM_obj_t {
     mp_obj_base_t base;
     pp_mat3_t transform;
 } _TRANSFORM_obj_t;
 
+typedef struct _VECTOR_obj_t {
+    mp_obj_base_t base;
+    PicoVector *vector;
+    _TRANSFORM_obj_t *transform;
+} _VECTOR_obj_t;
+
 typedef struct _POLY_obj_t {
     mp_obj_base_t base;
     pp_poly_t *poly;
@@ -566,7 +567,7 @@ mp_obj_t TRANSFORM_custom(mp_obj_t self_in, mp_obj_t custom_in) {
 
     pp_mat3_mul(&transform->transform, &t);
 
-    return mp_const_none;
+    return transform;
 }
 
 mp_obj_t TRANSFORM_rotate(mp_obj_t self_in, mp_obj_t angle_in, mp_obj_t origin_in) {
@@ -589,7 +590,7 @@ mp_obj_t TRANSFORM_rotate(mp_obj_t self_in, mp_obj_t angle_in, mp_obj_t origin_i
         pp_mat3_rotate(&transform->transform, angle);
     }
 
-    return mp_const_none;
+    return transform;
 }
 
 mp_obj_t TRANSFORM_translate(mp_obj_t self_in, mp_obj_t x_in, mp_obj_t y_in) {
@@ -600,7 +601,7 @@ mp_obj_t TRANSFORM_translate(mp_obj_t self_in, mp_obj_t x_in, mp_obj_t y_in) {
 
     pp_mat3_translate(&transform->transform, o_x, o_y);
 
-    return mp_const_none;
+    return transform;
 }
 
 mp_obj_t TRANSFORM_scale(mp_obj_t self_in, mp_obj_t x_in, mp_obj_t y_in) {
@@ -611,7 +612,7 @@ mp_obj_t TRANSFORM_scale(mp_obj_t self_in, mp_obj_t x_in, mp_obj_t y_in) {
 
     pp_mat3_scale(&transform->transform, o_x, o_y);
 
-    return mp_const_none;
+    return transform;
 }
 
 mp_obj_t TRANSFORM_reset(mp_obj_t self_in) {
@@ -645,22 +646,30 @@ mp_obj_t VECTOR_make_new(const mp_obj_type_t *type, size_t n_args, size_t n_kw,
 
 mp_obj_t VECTOR_set_transform(mp_obj_t self_in, mp_obj_t transform_in) {
     _VECTOR_obj_t *self = MP_OBJ_TO_PTR2(self_in, _VECTOR_obj_t);
-    (void)self;
 
     if(transform_in == mp_const_none) {
-        pp_mat3_t* old = pp_transform(NULL);
-        (void)old; // TODO: Return old transform?
+        pp_transform(NULL);
+        self->transform = NULL;
     } else if MP_OBJ_IS_TYPE(transform_in, &TRANSFORM_type) {
         _TRANSFORM_obj_t *transform = (_TRANSFORM_obj_t *)MP_OBJ_TO_PTR(transform_in);
-        pp_mat3_t* old = pp_transform(&transform->transform);
-        (void)old;
+        pp_transform(&transform->transform);
+
+        // Store a reference to the transform so `set_transform(Transform())`
+        // doesn't break when GC runs.
+        self->transform = transform;
     } else {
-        // TODO: ValueError?
+        mp_raise_ValueError("Must set a valid transform or None.");
     }
 
     return mp_const_none;
 }
 
+mp_obj_t VECTOR_get_transform(mp_obj_t self_in) {
+    _VECTOR_obj_t *self = MP_OBJ_TO_PTR2(self_in, _VECTOR_obj_t);
+
+    return self->transform ? self->transform : mp_const_none;
+}
+
 mp_obj_t VECTOR_set_font(mp_obj_t self_in, mp_obj_t font, mp_obj_t size) {
     _VECTOR_obj_t *self = MP_OBJ_TO_PTR2(self_in, _VECTOR_obj_t);
 

micropython/modules/picovector/picovector.h

@@ -47,6 +47,7 @@ extern mp_obj_t VECTOR_set_font_align(mp_obj_t self_in, mp_obj_t align);
 extern mp_obj_t VECTOR_set_antialiasing(mp_obj_t self_in, mp_obj_t aa);
 extern mp_obj_t VECTOR_set_transform(mp_obj_t self_in, mp_obj_t transform_in);
 extern mp_obj_t VECTOR_set_clip(mp_obj_t self_in, mp_obj_t clip_in);
+extern mp_obj_t VECTOR_get_transform(mp_obj_t self_in);
 
 extern mp_obj_t VECTOR_draw(mp_obj_t self_in, mp_obj_t poly_in);
 extern mp_obj_t VECTOR_rotate(size_t n_args, const mp_obj_t *pos_args, mp_map_t *kw_args);