feat(draw): add lv_draw_letter support (#7490)

Co-authored-by: Gabor Kiss-Vamosi <kisvegabor@gmail.com>

examples/widgets/canvas/index.rst

@@ -51,3 +51,15 @@ Draw a vector graphic to the canvas
 
 .. lv_example:: widgets/canvas/lv_example_canvas_8
   :language: c
+
+Draw Fancy Letter Effects
+-------------------------
+
+.. lv_example:: widgets/canvas/lv_example_canvas_9
+:language: c
+
+Draw Fancy Letter Effects 2
+---------------------------
+
+.. lv_example:: widgets/canvas/lv_example_canvas_10
+:language: c

examples/widgets/canvas/lv_example_canvas_10.c

@@ -0,0 +1,68 @@
+#include "../../lv_examples.h"
+#if LV_USE_CANVAS && LV_BUILD_EXAMPLES
+
+#define CANVAS_WIDTH  300
+#define CANVAS_HEIGHT  200
+
+static void timer_cb(lv_timer_t * timer)
+{
+    static int32_t counter = 0;
+    const char * string = "windstorrrrrrrrrrrrrrrrm~>>>";
+    const int16_t string_len = lv_strlen(string);
+
+    lv_obj_t * canvas = lv_timer_get_user_data(timer);
+    lv_layer_t layer;
+    lv_canvas_init_layer(canvas, &layer);
+
+    lv_canvas_fill_bg(canvas, lv_color_white(), LV_OPA_COVER);
+
+    lv_draw_letter_dsc_t letter_dsc;
+    lv_draw_letter_dsc_init(&letter_dsc);
+    letter_dsc.color = lv_color_hex(0xff0000);
+    letter_dsc.font = lv_font_default();
+
+    {
+#define CURVE2_X(t) ((t) * 2 + lv_trigo_cos((t) * 5) * 40 / 32767 - 10)
+#define CURVE2_Y(t, T) ((t) * lv_trigo_sin(((t) + (T)) * 5) * 40 / 32767 / 80 + CANVAS_HEIGHT / 2)
+
+        int32_t pre_x = CURVE2_X(-1);
+        int32_t pre_y = CURVE2_Y(-1, 0);
+        for(int16_t i = 0; i < string_len; i++) {
+            const int32_t angle = i * 5;
+            const int32_t x = CURVE2_X(angle);
+            const int32_t y = CURVE2_Y(angle + 30, counter / 2);
+
+            letter_dsc.unicode = (uint32_t)string[i % string_len];
+            letter_dsc.rotation = lv_atan2(y - pre_y, x - pre_x) * 10;
+            letter_dsc.color = lv_color_hsv_to_rgb(i * 10, 100, 100);
+            lv_draw_letter(&layer, &letter_dsc, &(lv_point_t) {
+                .x = x, .y = y
+            });
+
+            pre_x = x;
+            pre_y = y;
+        }
+    }
+
+    lv_canvas_finish_layer(canvas, &layer);
+
+    counter++;
+}
+
+void lv_example_canvas_10(void)
+{
+    /*Create a buffer for the canvas*/
+    LV_DRAW_BUF_DEFINE_STATIC(draw_buf, CANVAS_WIDTH, CANVAS_HEIGHT, LV_COLOR_FORMAT_ARGB8888);
+    LV_DRAW_BUF_INIT_STATIC(draw_buf);
+
+    lv_obj_t * canvas = lv_canvas_create(lv_screen_active());
+    lv_obj_set_size(canvas, CANVAS_WIDTH, CANVAS_HEIGHT);
+
+    lv_obj_center(canvas);
+
+    lv_canvas_set_draw_buf(canvas, &draw_buf);
+
+    lv_timer_create(timer_cb, 16, canvas);
+}
+
+#endif

examples/widgets/canvas/lv_example_canvas_9.c

@@ -0,0 +1,68 @@
+#include "../../lv_examples.h"
+#if LV_USE_CANVAS && LV_BUILD_EXAMPLES
+
+#define CANVAS_WIDTH  300
+#define CANVAS_HEIGHT  200
+
+static void timer_cb(lv_timer_t * timer)
+{
+    static int32_t counter = 0;
+    const char * string = "lol~ I'm wavvvvvvving~>>>";
+    const int16_t string_len = lv_strlen(string);
+
+    lv_obj_t * canvas = lv_timer_get_user_data(timer);
+    lv_layer_t layer;
+    lv_canvas_init_layer(canvas, &layer);
+
+    lv_canvas_fill_bg(canvas, lv_color_white(), LV_OPA_COVER);
+
+    lv_draw_letter_dsc_t letter_dsc;
+    lv_draw_letter_dsc_init(&letter_dsc);
+    letter_dsc.color = lv_color_hex(0xff0000);
+    letter_dsc.font = lv_font_default();
+
+    {
+#define CURVE2_X(t) (t * 2 + 10)
+#define CURVE2_Y(t) (lv_trigo_sin((t) * 5) * 40 / 32767 + CANVAS_HEIGHT / 2)
+
+        int32_t pre_x = CURVE2_X(-1);
+        int32_t pre_y = CURVE2_Y(-1);
+        for(int16_t i = 0; i < string_len; i++) {
+            const int32_t angle = i * 5;
+            const int32_t x = CURVE2_X(angle);
+            const int32_t y = CURVE2_Y(angle + counter / 2);
+
+            letter_dsc.unicode = (uint32_t)string[i % string_len];
+            letter_dsc.rotation = lv_atan2(y - pre_y, x - pre_x) * 10;
+            letter_dsc.color = lv_color_hsv_to_rgb(i * 10, 100, 100);
+            lv_draw_letter(&layer, &letter_dsc, &(lv_point_t) {
+                .x = x, .y = y
+            });
+
+            pre_x = x;
+            pre_y = y;
+        }
+    }
+
+    lv_canvas_finish_layer(canvas, &layer);
+
+    counter++;
+}
+
+void lv_example_canvas_9(void)
+{
+    /*Create a buffer for the canvas*/
+    LV_DRAW_BUF_DEFINE_STATIC(draw_buf, CANVAS_WIDTH, CANVAS_HEIGHT, LV_COLOR_FORMAT_ARGB8888);
+    LV_DRAW_BUF_INIT_STATIC(draw_buf);
+
+    lv_obj_t * canvas = lv_canvas_create(lv_screen_active());
+    lv_obj_set_size(canvas, CANVAS_WIDTH, CANVAS_HEIGHT);
+
+    lv_obj_center(canvas);
+
+    lv_canvas_set_draw_buf(canvas, &draw_buf);
+
+    lv_timer_create(timer_cb, 16, canvas);
+}
+
+#endif