Improve legibility of scrolling text.

Author: markshannon

examples/compass.py

@@ -7,9 +7,7 @@
 # You need to spin the microbit about a few times to help calibrate the compass
 
 # Scroll a message to encourage user to help calibrate the compass
-# "Spin" "Me!" reads better than "Spin Me!" due to lack of kerning
-display.scroll("Spin")
-display.scroll("Me!")
+display.scroll("Spin Me!")
 
 # Start calibrating
 compass.calibrate()

inc/genhdr/qstrdefs.generated.h

@@ -305,6 +305,7 @@ QDEF(MP_QSTR_shift_left, (const byte*)"\xa1\x0a" "shift_left")
 QDEF(MP_QSTR_shift_right, (const byte*)"\xba\x0b" "shift_right")
 QDEF(MP_QSTR_shift_up, (const byte*)"\xdf\x08" "shift_up")
 QDEF(MP_QSTR_shift_down, (const byte*)"\x48\x0a" "shift_down")
+QDEF(MP_QSTR_monospace, (const byte*)"\xe2\x09" "monospace")
 QDEF(MP_QSTR_HEART, (const byte*)"\x0f\x05" "HEART")
 QDEF(MP_QSTR_HEART_SMALL, (const byte*)"\xcf\x0b" "HEART_SMALL")
 QDEF(MP_QSTR_HAPPY, (const byte*)"\x15\x05" "HAPPY")

inc/microbit/MicroBitCustomConfig.h

@@ -19,4 +19,7 @@
 #define MICROBIT_BLE_EVENT_SERVICE  0
 #define MICROBIT_BLE_DEVICE_INFORMATION_SERVICE     0
 
+// Slow this down a bit as proportional spacing reduces length
+#define MICROBIT_DEFAULT_SCROLL_SPEED       150
+
 #endif

inc/microbit/microbitimage.h

@@ -63,7 +63,7 @@ typedef union _microbit_image_obj_t {
 microbit_image_obj_t *microbit_image_for_char(char c);
 mp_obj_t microbit_image_slice(microbit_image_obj_t *img, mp_int_t start, mp_int_t width, mp_int_t stride);
 /* ref exists so that we can pull a string out of an object and not have it GC'ed while oterating over it */
-mp_obj_t scrolling_string_image_iterable(const char* str, mp_uint_t len, mp_obj_t ref);
+mp_obj_t scrolling_string_image_iterable(const char* str, mp_uint_t len, mp_obj_t ref, bool monospace);
 
 #define SMALL_IMAGE(p0, p1, p2, p3, p4, p5, p6, p7, p8, p9, p10, p11, p12, p13, p14, p15, p16, p17, p18, p19, p20, p21, p22, p23, p44) \
 { \

inc/microbit/qstrdefsport.h

@@ -63,6 +63,7 @@ Q(shift_left)
 Q(shift_right)
 Q(shift_up)
 Q(shift_down)
+Q(monospace)
 Q(HEART)
 Q(HEART_SMALL)
 Q(HAPPY)

source/microbit/microbitdisplay.cpp

@@ -352,25 +352,26 @@ STATIC mp_obj_t microbit_display_animate_func(mp_uint_t n_args, const mp_obj_t *
 MP_DEFINE_CONST_FUN_OBJ_KW(microbit_display_animate_obj, 2, microbit_display_animate_func);
 
 void microbit_display_scroll(microbit_display_obj_t *self, const char* str, mp_int_t len, bool wait) {
-    mp_obj_t iterable = scrolling_string_image_iterable(str, len, NULL);
+    mp_obj_t iterable = scrolling_string_image_iterable(str, len, NULL, false);
     microbit_display_animate(self, iterable, MICROBIT_DEFAULT_SCROLL_SPEED, wait, false);
 }
 
 
 mp_obj_t microbit_display_scroll_func(mp_uint_t n_args, const mp_obj_t *pos_args, mp_map_t *kw_args) {
     static const mp_arg_t scroll_allowed_args[] = {
-        { MP_QSTR_text,     MP_ARG_REQUIRED | MP_ARG_OBJ, {.u_obj = MP_OBJ_NULL} },
-        { MP_QSTR_delay,    MP_ARG_INT, {.u_int = MICROBIT_DEFAULT_SCROLL_SPEED} },
-        { MP_QSTR_wait,     MP_ARG_KW_ONLY | MP_ARG_BOOL, {.u_bool = true} },
-        { MP_QSTR_loop,     MP_ARG_KW_ONLY | MP_ARG_BOOL, {.u_bool = false} },
+        { MP_QSTR_text, MP_ARG_REQUIRED | MP_ARG_OBJ, {.u_obj = MP_OBJ_NULL} },
+        { MP_QSTR_delay, MP_ARG_INT, {.u_int = MICROBIT_DEFAULT_SCROLL_SPEED} },
+        { MP_QSTR_wait, MP_ARG_KW_ONLY | MP_ARG_BOOL, {.u_bool = true} },
+        { MP_QSTR_loop, MP_ARG_KW_ONLY | MP_ARG_BOOL, {.u_bool = false} },
+        { MP_QSTR_monospace, MP_ARG_KW_ONLY | MP_ARG_BOOL, {.u_bool = false} },
     };
     // Parse the args.
     microbit_display_obj_t *self = (microbit_display_obj_t*)pos_args[0];
     mp_arg_val_t args[MP_ARRAY_SIZE(scroll_allowed_args)];
     mp_arg_parse_all(n_args - 1, pos_args + 1, kw_args, MP_ARRAY_SIZE(scroll_allowed_args), scroll_allowed_args, args);
     mp_uint_t len;
     const char* str = mp_obj_str_get_data(args[0].u_obj, &len);
-    mp_obj_t iterable = scrolling_string_image_iterable(str, len, args[0].u_obj);
+    mp_obj_t iterable = scrolling_string_image_iterable(str, len, args[0].u_obj, args[4].u_bool /*monospace?*/);
     microbit_display_animate(self, iterable, args[1].u_int /*delay*/, args[2].u_bool/*wait?*/, args[3].u_bool /*loop?*/);
     return mp_const_none;
 }

source/microbit/microbitimage.cpp

@@ -517,15 +517,15 @@ STATIC const unsigned char *get_font_data_from_char(char c) {
 
 STATIC mp_int_t get_pixel_from_font_data(const unsigned char *data, int x, int y) {
     /* The following logic belongs in MicroBitFont */
-    return ((data[y]>>(4-x))&1)*MAX_BRIGHTNESS;
+    return ((data[y]>>(4-x))&1);
 }
 
 microbit_image_obj_t *microbit_image_for_char(char c) {
     const unsigned char *data = get_font_data_from_char(c);
     greyscale_t *result = greyscale_new(5,5);
     for (int x = 0; x < 5; ++x) {
         for (int y = 0; y < 5; ++y) {
-            result->setPixelValue(x, y, get_pixel_from_font_data(data, x, y));
+            result->setPixelValue(x, y, get_pixel_from_font_data(data, x, y)*MAX_BRIGHTNESS);
         }
     }
     return (microbit_image_obj_t *)result;
@@ -702,6 +702,7 @@ typedef struct _scrolling_string_t {
     char const *str;
     mp_uint_t len;
     mp_obj_t ref;
+    bool monospace;
 } scrolling_string_t;
 
 typedef struct _scrolling_string_iterator_t {
@@ -711,21 +712,44 @@ typedef struct _scrolling_string_iterator_t {
     char const *next_char;
     char const *end;
     uint8_t offset;
+    uint8_t offset_limit;
+    bool monospace;
     char right;
 } scrolling_string_iterator_t;
 
 extern const mp_obj_type_t microbit_scrolling_string_type;
 extern const mp_obj_type_t microbit_scrolling_string_iterator_type;
 
-mp_obj_t scrolling_string_image_iterable(const char* str, mp_uint_t len, mp_obj_t ref) {
+mp_obj_t scrolling_string_image_iterable(const char* str, mp_uint_t len, mp_obj_t ref, bool monospace) {
     scrolling_string_t *result = m_new_obj(scrolling_string_t);
     result->base.type = &microbit_scrolling_string_type;
     result->str = str;
     result->len = len;
     result->ref = ref;
+    result->monospace = monospace;
     return result;
 }
 
+STATIC int font_column_non_blank(const unsigned char *font_data, unsigned int col) {
+    for (int y = 0; y < 5; ++y) {
+        if (get_pixel_from_font_data(font_data, col, y)) {
+            return 1;
+        }
+    }
+    return 0;
+}
+
+/* Not strictly the rightmost non-blank column, but the rightmost in columns 2,3 or 4. */
+STATIC unsigned int rightmost_non_blank_column(const unsigned char *font_data) {
+    if (font_column_non_blank(font_data, 4)) {
+        return 4;
+    }
+    if (font_column_non_blank(font_data, 3)) {
+        return 3;
+    }
+    return 2;
+}
+
 STATIC mp_obj_t get_microbit_scrolling_string_iter(mp_obj_t o_in) {
     scrolling_string_t *str = (scrolling_string_t *)o_in;
     scrolling_string_iterator_t *result = m_new_obj(scrolling_string_iterator_t);
@@ -734,11 +758,19 @@ STATIC mp_obj_t get_microbit_scrolling_string_iter(mp_obj_t o_in) {
     result->offset = 0;
     result->next_char = str->str;
     result->ref = str->ref;
+    result->monospace = str->monospace;
     result->end = result->next_char + str->len;
-    if (str->len)
+    if (str->len) {
         result->right = *result->next_char;
-    else
+        if (result->monospace) {
+            result->offset_limit = 5;
+        } else {
+            result->offset_limit = rightmost_non_blank_column(get_font_data_from_char(result->right)) + 1;
+        }
+    } else {
         result->right = ' ';
+        result->offset_limit = 5;
+    }
     return result;
 }
 
@@ -749,19 +781,30 @@ STATIC mp_obj_t microbit_scrolling_string_iter_next(mp_obj_t o_in) {
     }
     greyscale_t *result = iter->img->shiftLeft(1);
     iter->img = (microbit_image_obj_t*)result;
-    const unsigned char *font_data = get_font_data_from_char(iter->right);
-    if (iter->offset < 5) {
+    const unsigned char *font_data;
+    if (iter->offset < iter->offset_limit) {
+        font_data = get_font_data_from_char(iter->right);
         for (int y = 0; y < 5; ++y) {
-            int pix = get_pixel_from_font_data(font_data, iter->offset, y);
+            int pix = get_pixel_from_font_data(font_data, iter->offset, y)*MAX_BRIGHTNESS;
             result->setPixelValue(4, y, pix);
         }
-    } else if (iter->offset == 6) {
+    } else if (iter->offset == iter->offset_limit) {
         ++iter->next_char;
-        if (iter->next_char == iter->end)
+        if (iter->next_char == iter->end) {
             iter->right = ' ';
-        else
+            iter->offset_limit = 5;
+            iter->offset = 0;
+        } else {
             iter->right = *iter->next_char;
-        iter->offset = -1;
+            font_data = get_font_data_from_char(iter->right);
+            if (iter->monospace) {
+                iter->offset = -1;
+                iter->offset_limit = 5;
+            } else {
+                iter->offset = -font_column_non_blank(font_data, 0);
+                iter->offset_limit = rightmost_non_blank_column(font_data)+1;
+            }
+        }
     }
     ++iter->offset;
     return result;