feat(canvas) add lv_canvas_set_px_opa

fixes #2665

docs/widgets/core/canvas.md

@@ -33,10 +33,13 @@ For `LV_IMG_CF_INDEXED_1/2/4/8` color formats a palette needs to be
 initialized with  `lv_canvas_set_palette(canvas, 3, LV_COLOR_RED)`. It sets pixels with *index=3* to red.
 
 ### Drawing
-To set a pixel on the canvas, use `lv_canvas_set_px(canvas, x, y, LV_COLOR_RED)`.
+To set a pixel's color on the canvas, use `lv_canvas_set_px_color(canvas, x, y, LV_COLOR_RED)`.
-With `LV_IMG_CF_INDEXED_...` or `LV_IMG_CF_ALPHA_...`, the index of the color or the alpha value needs to be passed as color. 
+With `LV_IMG_CF_INDEXED_...`  the index of the color needs to be passed as color. 
 E.g. `lv_color_t c; c.full = 3;`
 
+To set a pixel's opacity with `LV_IMG_CF_TRUE_COLOR_ALPHA` or `LV_IMG_CF_ALPHA_...` format on the canvas, use `lv_canvas_set_px_opa(canvas, x, y, opa)`.
+
+
 `lv_canvas_fill_bg(canvas, LV_COLOR_BLUE, LV_OPA_50)` fills the whole canvas to blue with 50% opacity. Note that if the current color format doesn't support colors (e.g. `LV_IMG_CF_ALPHA_2BIT`) the color will be ignored. 
 Similarly, if opacity is not supported (e.g. `LV_IMG_CF_TRUE_COLOR`) it will be ignored.
 

examples/widgets/canvas/lv_example_canvas_2.c

@@ -36,7 +36,7 @@ void lv_example_canvas_2(void)
     uint32_t y;
     for( y = 10; y < 30; y++) {
         for( x = 5; x < 20; x++) {
-            lv_canvas_set_px(canvas, x, y, c0);
+            lv_canvas_set_px_color(canvas, x, y, c0);
         }
     }
 

src/extra/libs/qrcode/lv_qrcode.c

@@ -120,7 +120,7 @@ lv_res_t lv_qrcode_update(lv_obj_t * qrcode, const void * data, uint32_t data_le
 
             if(aligned == false) {
                 c.full = a ? 0 : 1;
-                lv_canvas_set_px(qrcode, x, y, c);
+                lv_canvas_set_px_color(qrcode, x, y, c);
             } else {
                 if(!a) b |= (1 << (7 - p));
                 p++;

src/widgets/lv_canvas.c

@@ -74,7 +74,7 @@ void lv_canvas_set_buffer(lv_obj_t * obj, void * buf, lv_coord_t w, lv_coord_t h
     lv_img_set_src(obj, &canvas->dsc);
 }
 
-void lv_canvas_set_px(lv_obj_t * obj, lv_coord_t x, lv_coord_t y, lv_color_t c)
+void lv_canvas_set_px_color(lv_obj_t * obj, lv_coord_t x, lv_coord_t y, lv_color_t c)
 {
     LV_ASSERT_OBJ(obj, MY_CLASS);
 
@@ -84,6 +84,16 @@ void lv_canvas_set_px(lv_obj_t * obj, lv_coord_t x, lv_coord_t y, lv_color_t c)
     lv_obj_invalidate(obj);
 }
 
+void lv_canvas_set_px_opa(lv_obj_t * obj, lv_coord_t x, lv_coord_t y, lv_opa_t opa)
+{
+    LV_ASSERT_OBJ(obj, MY_CLASS);
+
+    lv_canvas_t * canvas = (lv_canvas_t *)obj;
+
+    lv_img_buf_set_px_alpha(&canvas->dsc, x, y, opa);
+    lv_obj_invalidate(obj);
+}
+
 void lv_canvas_set_palette(lv_obj_t * obj, uint8_t id, lv_color_t c)
 {
     LV_ASSERT_OBJ(obj, MY_CLASS);

src/widgets/lv_canvas.h

@@ -70,9 +70,27 @@ void lv_canvas_set_buffer(lv_obj_t * canvas, void * buf, lv_coord_t w, lv_coord_
  * @param canvas
  * @param x x coordinate of the point to set
  * @param y x coordinate of the point to set
- * @param c color of the point
+ * @param c color of the pixel
  */
-void lv_canvas_set_px(lv_obj_t * canvas, lv_coord_t x, lv_coord_t y, lv_color_t c);
+void lv_canvas_set_px_color(lv_obj_t * canvas, lv_coord_t x, lv_coord_t y, lv_color_t c);
+
+/**
+ * DEPRECATED: added only for backward compatibility
+ */
+static inline void lv_canvas_set_px(lv_obj_t * canvas, lv_coord_t x, lv_coord_t y, lv_color_t c)
+{
+    lv_canvas_set_px_color(canvas, x, y, c);
+}
+
+/**
+ * Set the opacity of a pixel on the canvas
+ * @param canvas
+ * @param x x coordinate of the point to set
+ * @param y x coordinate of the point to set
+ * @param opa opacity of the pixel (0..255)
+ */
+void lv_canvas_set_px_opa(lv_obj_t * canvas, lv_coord_t x, lv_coord_t y, lv_opa_t opa);
+
 
 /**
  * Set the palette color of a canvas with index format. Valid only for `LV_IMG_CF_INDEXED1/2/4/8`