diff --git a/src/draw/lv_draw.h b/src/draw/lv_draw.h
index 0db5dbbbfa..b143f2c34a 100644
--- a/src/draw/lv_draw.h
+++ b/src/draw/lv_draw.h
@@ -203,8 +203,14 @@ typedef struct {
  * GLOBAL PROTOTYPES
  **********************/
 
+/**
+ * Used internally to initialize the drawing module
+ */
 void lv_draw_init(void);
 
+/**
+ * Deinitialize the drawing module
+ */
 void lv_draw_deinit(void);
 
 /**
@@ -214,12 +220,35 @@ void lv_draw_deinit(void);
  */
 void * lv_draw_create_unit(size_t size);
 
+/**
+ * Add an empty draw task to the draw task list of a layer.
+ * @param layer     pointer to a layer
+ * @param coords    the coordinates of the draw task
+ * @return          the created draw task which needs to be
+ *                  further configured e.g. by added a draw descriptor
+ */
 lv_draw_task_t * lv_draw_add_task(lv_layer_t * layer, const lv_area_t * coords);
 
+/**
+ * Needs to be called when a draw task is created and configured.
+ * It will send an event about the new draw task to the widget
+ * and assign it to a draw unit.
+ * @param layer     pointer to a layer
+ * @param t         poinr to a draw task
+ */
 void lv_draw_finalize_task_creation(lv_layer_t * layer, lv_draw_task_t * t);
 
+/**
+ * Try dispatching draw tasks to draw units
+ */
 void lv_draw_dispatch(void);
 
+/**
+ * Used internally to try dispatching draw tasks of a specific layer
+ * @param disp      pointer to a display on which the dispatching was requested
+ * @param layer     pointer to a layer
+ * @return          at least one draw task is being rendered (maybe it was taken earlier)
+ */
 bool lv_draw_dispatch_layer(struct _lv_display_t * disp, lv_layer_t * layer);
 
 /**
@@ -228,6 +257,10 @@ bool lv_draw_dispatch_layer(struct _lv_display_t * disp, lv_layer_t * layer);
  */
 void lv_draw_dispatch_wait_for_request(void);
 
+/**
+ * When a draw unit finished a draw task it needs to request dispatching
+ * to let LVGL assign a new draw task to it
+ */
 void lv_draw_dispatch_request(void);
 
 /**
diff --git a/src/draw/lv_draw_arc.h b/src/draw/lv_draw_arc.h
index ec39c698de..c05302590a 100644
--- a/src/draw/lv_draw_arc.h
+++ b/src/draw/lv_draw_arc.h
@@ -25,6 +25,7 @@ extern "C" {
 /**********************
  *      TYPEDEFS
  **********************/
+
 typedef struct {
     lv_draw_dsc_base_t base;
 
@@ -45,8 +46,17 @@ struct _lv_layer_t;
  * GLOBAL PROTOTYPES
  **********************/
 
+/**
+ * Initialize an arc draw descriptor.
+ * @param dsc       pointer to a draw descriptor
+ */
 void lv_draw_arc_dsc_init(lv_draw_arc_dsc_t * dsc);
 
+/**
+ * Create an arc draw task.
+ * @param layer         pointer to a layer
+ * @param dsc           pointer to an initialized draw descriptor variable
+ */
 void lv_draw_arc(struct _lv_layer_t * layer, const lv_draw_arc_dsc_t * dsc);
 
 /**
diff --git a/src/draw/lv_draw_image.h b/src/draw/lv_draw_image.h
index 044970e938..48915b7b29 100644
--- a/src/draw/lv_draw_image.h
+++ b/src/draw/lv_draw_image.h
@@ -78,20 +78,24 @@ struct _lv_layer_t;
  * GLOBAL PROTOTYPES
  **********************/
 
+/**
+ * Initialize an image draw descriptor.
+ * @param dsc       pointer to a draw descriptor
+ */
 void lv_draw_image_dsc_init(lv_draw_image_dsc_t * dsc);
 
 /**
- * Draw an image
+ * Create an image draw task
  * @param layer         pointer to a layer
- * @param dsc           pointer to an initialized `lv_draw_image_dsc_t` variable
+ * @param dsc           pointer to an initialized draw descriptor
  * @param coords        the coordinates of the image
  */
 void lv_draw_image(struct _lv_layer_t * layer, const lv_draw_image_dsc_t * dsc, const lv_area_t * coords);
 
 /**
- * Draw a layer on an other layer
+ * Create a draw task to blend a layer to an other layer
  * @param layer         pointer to a layer
- * @param dsc           pointer to an initialized `lv_draw_image_dsc_t` variable
+ * @param dsc           pointer to an initialized draw descriptor
  * @param coords        the coordinates of the layer
  */
 void lv_draw_layer(struct _lv_layer_t * layer, const lv_draw_image_dsc_t * dsc, const lv_area_t * coords);
diff --git a/src/draw/lv_draw_label.c b/src/draw/lv_draw_label.c
index 3eb5f728a0..affaa8ebe3 100644
--- a/src/draw/lv_draw_label.c
+++ b/src/draw/lv_draw_label.c
@@ -29,7 +29,7 @@
  *  STATIC PROTOTYPES
  **********************/
 static void draw_letter(lv_draw_unit_t * draw_unit, lv_draw_glyph_dsc_t * dsc,  const lv_point_t * pos,
-                        const lv_font_t * font, uint32_t letter, lv_draw_letter_cb_t cb);
+                        const lv_font_t * font, uint32_t letter, lv_draw_glyph_cb_t cb);
 
 /**********************
  *  STATIC VARIABLES
@@ -61,7 +61,7 @@ void lv_draw_label_dsc_init(lv_draw_label_dsc_t * dsc)
     dsc->base.dsc_size = sizeof(lv_draw_label_dsc_t);
 }
 
-void lv_draw_letter_dsc_init(lv_draw_glyph_dsc_t * dsc)
+void lv_draw_glyph_dsc_init(lv_draw_glyph_dsc_t * dsc)
 {
     lv_memzero(dsc, sizeof(lv_draw_glyph_dsc_t));
 }
@@ -93,8 +93,8 @@ LV_ATTRIBUTE_FAST_MEM void lv_draw_label(lv_layer_t * layer, const lv_draw_label
     LV_PROFILER_END;
 }
 
-LV_ATTRIBUTE_FAST_MEM void lv_draw_letter(lv_layer_t * layer, lv_draw_label_dsc_t * dsc,
-                                          const lv_point_t * point, uint32_t unicode_letter)
+LV_ATTRIBUTE_FAST_MEM void lv_draw_character(lv_layer_t * layer, lv_draw_label_dsc_t * dsc,
+                                             const lv_point_t * point, uint32_t unicode_letter)
 {
     if(dsc->opa <= LV_OPA_MIN) return;
     if(dsc->font == NULL) {
@@ -133,9 +133,9 @@ LV_ATTRIBUTE_FAST_MEM void lv_draw_letter(lv_layer_t * layer, lv_draw_label_dsc_
     LV_PROFILER_END;
 }
 
-void lv_draw_label_iterate_letters(lv_draw_unit_t * draw_unit, const lv_draw_label_dsc_t * dsc,
-                                   const lv_area_t * coords,
-                                   lv_draw_letter_cb_t cb)
+void lv_draw_label_iterate_characters(lv_draw_unit_t * draw_unit, const lv_draw_label_dsc_t * dsc,
+                                      const lv_area_t * coords,
+                                      lv_draw_glyph_cb_t cb)
 {
     const lv_font_t * font = dsc->font;
     int32_t w;
@@ -236,7 +236,7 @@ void lv_draw_label_iterate_letters(lv_draw_unit_t * draw_unit, const lv_draw_lab
 
     lv_area_t bg_coords;
     lv_draw_glyph_dsc_t draw_letter_dsc;
-    lv_draw_letter_dsc_init(&draw_letter_dsc);
+    lv_draw_glyph_dsc_init(&draw_letter_dsc);
     draw_letter_dsc.opa = dsc->opa;
     draw_letter_dsc.bg_coords = &bg_coords;
     draw_letter_dsc.color = dsc->color;
@@ -365,7 +365,7 @@ void lv_draw_label_iterate_letters(lv_draw_unit_t * draw_unit, const lv_draw_lab
  **********************/
 
 static void draw_letter(lv_draw_unit_t * draw_unit, lv_draw_glyph_dsc_t * dsc,  const lv_point_t * pos,
-                        const lv_font_t * font, uint32_t letter, lv_draw_letter_cb_t cb)
+                        const lv_font_t * font, uint32_t letter, lv_draw_glyph_cb_t cb)
 {
     lv_font_glyph_dsc_t g;
 
diff --git a/src/draw/lv_draw_label.h b/src/draw/lv_draw_label.h
index 69869dee7c..3f6bd9df82 100644
--- a/src/draw/lv_draw_label.h
+++ b/src/draw/lv_draw_label.h
@@ -29,6 +29,7 @@ extern "C" {
  **********************/
 
 struct _lv_layer_t;
+
 /** Store some info to speed up drawing of very large texts
  * It takes a lot of time to get the first visible character because
  * all the previous characters needs to be checked to calculate the positions.
@@ -76,55 +77,81 @@ typedef struct {
 typedef enum {
     LV_DRAW_LETTER_BITMAP_FORMAT_A8,
     LV_DRAW_LETTER_BITMAP_FORMAT_IMAGE,
-} lv_draw_letter_bitmap_format_t;
+} lv_draw_glyph_bitmap_format_t;
 
 typedef struct {
     const uint8_t * bitmap;
     uint8_t * _bitmap_buf_unaligned;
     uint8_t * bitmap_buf;
     uint32_t _bitmap_buf_size;
-    lv_draw_letter_bitmap_format_t format;
+    lv_draw_glyph_bitmap_format_t format;
     const lv_area_t * letter_coords;
     const lv_area_t * bg_coords;
     lv_color_t color;
     lv_opa_t opa;
 } lv_draw_glyph_dsc_t;
 
-typedef void(*lv_draw_letter_cb_t)(lv_draw_unit_t * draw_unit, lv_draw_glyph_dsc_t * dsc, lv_draw_fill_dsc_t * fill_dsc,
-                                   const lv_area_t * fill_area);
-
-void lv_draw_label_iterate_letters(lv_draw_unit_t * draw_unit, const lv_draw_label_dsc_t * dsc,
-                                   const lv_area_t * coords,
-                                   lv_draw_letter_cb_t cb);
+/**
+ * Passed as a parameter to `lv_draw_label_iterate_characters` to
+ * draw the characters one by one
+ * @param draw_unit     pointer to a draw unit
+ * @param dsc           pointer to `lv_draw_glyph_dsc_t` to describe the character to draw
+ *                      if NULL don't draw character
+ * @param fill_dsc      pointer to a fill descriptor to draw a background for the character or
+ *                      underline or strike through
+ *                      if NULL do not fill anything
+ * @param fill_area     the area to fill
+ *                      if NULL do not fill anything
+ */
+typedef void(*lv_draw_glyph_cb_t)(lv_draw_unit_t * draw_unit, lv_draw_glyph_dsc_t * dsc, lv_draw_fill_dsc_t * fill_dsc,
+                                  const lv_area_t * fill_area);
 
 /**********************
  * GLOBAL PROTOTYPES
  **********************/
 
+/**
+ * Initialize a label draw descriptor
+ * @param dsc       pointer to a draw descriptor
+ */
 LV_ATTRIBUTE_FAST_MEM void lv_draw_label_dsc_init(lv_draw_label_dsc_t * dsc);
 
-void lv_draw_letter_dsc_init(lv_draw_glyph_dsc_t * dsc);
+/**
+ * Initialize a glyph draw descriptor.
+ * Used internally.
+ * @param dsc       pointer to a draw descriptor
+ */
+void lv_draw_glyph_dsc_init(lv_draw_glyph_dsc_t * dsc);
 
 /**
- * Write a text
+ * Crate a draw task to render a text
  * @param layer         pointer to a layer
  * @param dsc           pointer to draw descriptor
- * @param coords        coordinates of the label
- * It is managed by the draw to speed up the drawing of very long texts (thousands of lines).
+ * @param coords        coordinates of the character
  */
 LV_ATTRIBUTE_FAST_MEM void lv_draw_label(lv_layer_t * layer, const lv_draw_label_dsc_t * dsc,
                                          const lv_area_t * coords);
 
 /**
- * Write a text
+ * Crate a draw task to render a single character
  * @param layer          pointer to a layer
  * @param dsc            pointer to draw descriptor
  * @param point          position of the label
  * @param unicode_letter the letter to draw
- * It is managed by the draw to speed up the drawing of very long texts (thousands of lines).
  */
-LV_ATTRIBUTE_FAST_MEM void lv_draw_letter(lv_layer_t * layer, lv_draw_label_dsc_t * dsc,
-                                          const lv_point_t * point, uint32_t unicode_letter);
+LV_ATTRIBUTE_FAST_MEM void lv_draw_character(lv_layer_t * layer, lv_draw_label_dsc_t * dsc,
+                                             const lv_point_t * point, uint32_t unicode_letter);
+
+/**
+ * Should be used during rendering the characters to get the position and other
+ * parameters of the characters
+ * @param draw_unit     pointer to a draw unit
+ * @param dsc           pointer to draw descriptor
+ * @param coords        coordinates of the label
+ * @param cb            a callback to call to draw each glyphs one by one
+ */
+void lv_draw_label_iterate_characters(lv_draw_unit_t * draw_unit, const lv_draw_label_dsc_t * dsc,
+                                      const lv_area_t * coords, lv_draw_glyph_cb_t cb);
 
 /***********************
  * GLOBAL VARIABLES
diff --git a/src/draw/lv_draw_line.h b/src/draw/lv_draw_line.h
index bb2418f5e8..021ea0588e 100644
--- a/src/draw/lv_draw_line.h
+++ b/src/draw/lv_draw_line.h
@@ -47,12 +47,16 @@ struct _lv_layer_t;
  * GLOBAL PROTOTYPES
  **********************/
 
-LV_ATTRIBUTE_FAST_MEM void lv_draw_line_dsc_init(lv_draw_line_dsc_t * dsc);
+/**
+ * Initialize a line draw descriptor
+ * @param dsc       pointer to a draw descriptor
+ */
+void lv_draw_line_dsc_init(lv_draw_line_dsc_t * dsc);
 
 /**
- * Draw a line
- * @param layer         pointer to a layer
- * @param dsc           pointer to an initialized `lv_draw_line_dsc_t` variable
+ * Create a line draw task
+ * @param layer     pointer to a layer
+ * @param dsc       pointer to an initialized `lv_draw_line_dsc_t` variable
  */
 void lv_draw_line(struct _lv_layer_t * layer, const lv_draw_line_dsc_t * dsc);
 
diff --git a/src/draw/lv_draw_mask.h b/src/draw/lv_draw_mask.h
index 6c65e4f47e..bece9c8564 100644
--- a/src/draw/lv_draw_mask.h
+++ b/src/draw/lv_draw_mask.h
@@ -38,14 +38,16 @@ struct _lv_layer_t;
  * GLOBAL PROTOTYPES
  **********************/
 
+/**
+ * Initialize a rectangle mask draw descriptor.
+ * @param dsc       pointer to a draw descriptor
+ */
 LV_ATTRIBUTE_FAST_MEM void lv_draw_mask_rect_dsc_init(lv_draw_mask_rect_dsc_t * dsc);
 
 /**
- * Draw a line
- * @param point1 first point of the line
- * @param point2 second point of the line
- * @param clip the line will be drawn only in this area
- * @param dsc pointer to an initialized `lv_draw_line_dsc_t` variable
+ * Create a draw task to mask a rectangle from the buffer
+ * @param layer     pointer to a layer
+ * @param dsc       pointer to a draw descriptor
  */
 void lv_draw_mask_rect(struct _lv_layer_t * layer, const lv_draw_mask_rect_dsc_t * dsc);
 
diff --git a/src/draw/lv_draw_rect.h b/src/draw/lv_draw_rect.h
index 3d26b28476..a8399686b4 100644
--- a/src/draw/lv_draw_rect.h
+++ b/src/draw/lv_draw_rect.h
@@ -109,18 +109,35 @@ typedef struct {
  * GLOBAL PROTOTYPES
  **********************/
 
+/**
+ * Initialize a rectangle draw descriptor.
+ * @param dsc       pointer to a draw descriptor
+ */
 LV_ATTRIBUTE_FAST_MEM void lv_draw_rect_dsc_init(lv_draw_rect_dsc_t * dsc);
 
+/**
+ * Initialize a fill draw descriptor.
+ * @param dsc       pointer to a draw descriptor
+ */
 void lv_draw_fill_dsc_init(lv_draw_fill_dsc_t * dsc);
 
+/**
+ * Initialize a border draw descriptor.
+ * @param dsc       pointer to a draw descriptor
+ */
 void lv_draw_border_dsc_init(lv_draw_border_dsc_t * dsc);
 
+/**
+ * Initialize a box shadow draw descriptor.
+ * @param dsc       pointer to a draw descriptor
+ */
 void lv_draw_box_shadow_dsc_init(lv_draw_box_shadow_dsc_t * dsc);
 
 /**
- * Draw a rectangle
+ * The rectangle is a wrapper for fill, border, bg. image and box shadow.
+ * Internally fill, border, image and box shadow draw tasks will be created.
  * @param layer         pointer to a layer
- * @param dsc           pointer to an initialized `lv_draw_rect_dsc_t` variable
+ * @param dsc           pointer to an initialized draw descriptor variable
  * @param coords        the coordinates of the rectangle
  */
 void lv_draw_rect(struct _lv_layer_t * layer, const lv_draw_rect_dsc_t * dsc, const lv_area_t * coords);
diff --git a/src/draw/lv_draw_triangle.h b/src/draw/lv_draw_triangle.h
index 2f34d3b9b5..682dbfea19 100644
--- a/src/draw/lv_draw_triangle.h
+++ b/src/draw/lv_draw_triangle.h
@@ -36,8 +36,17 @@ typedef struct {
  * GLOBAL PROTOTYPES
  **********************/
 
+/**
+ * Initialize a triangle draw descriptor
+ * @param dsc       pointer to a draw descriptor
+ */
 void lv_draw_triangle_dsc_init(lv_draw_triangle_dsc_t * draw_dsc);
 
+/**
+ * Create a triangle draw task
+ * @param layer     pointer to a layer
+ * @param dsc       pointer to an initialized `lv_draw_triangle_dsc_t` variable
+ */
 void lv_draw_triangle(struct _lv_layer_t * layer, const lv_draw_triangle_dsc_t * draw_dsc);
 
 /**********************
diff --git a/src/draw/lv_draw_vector.h b/src/draw/lv_draw_vector.h
index a55534b242..87f22d4c6b 100644
--- a/src/draw/lv_draw_vector.h
+++ b/src/draw/lv_draw_vector.h
@@ -526,7 +526,9 @@ void lv_draw_vector(lv_vector_dsc_t * dsc);
 
 /* Traverser for task list */
 typedef void (*vector_draw_task_cb)(void * ctx, const lv_vector_path_t * path, const lv_vector_draw_dsc_t * dsc);
+
 void _lv_vector_for_each_destroy_tasks(lv_ll_t * task_list, vector_draw_task_cb cb, void * data);
+
 #endif /* LV_USE_VECTOR_GRAPHIC */
 
 #ifdef __cplusplus
diff --git a/src/draw/lv_image_buf.h b/src/draw/lv_image_buf.h
index 79e5199a4c..291e7a37f9 100644
--- a/src/draw/lv_image_buf.h
+++ b/src/draw/lv_image_buf.h
@@ -141,13 +141,13 @@ typedef struct {
  **********************/
 
 /**
- * Set the palette color of an indexed image. Valid only for `LV_IMAGE_CF_INDEXED1/2/4/8`
+ * Set the palette color of an indexed image. Valid only for `LV_COLOR_FORMAT_I1/2/4/8`
  * @param dsc pointer to an image descriptor
  * @param id the palette color to set:
- *   - for `LV_IMAGE_CF_INDEXED1`: 0..1
- *   - for `LV_IMAGE_CF_INDEXED2`: 0..3
- *   - for `LV_IMAGE_CF_INDEXED4`: 0..15
- *   - for `LV_IMAGE_CF_INDEXED8`: 0..255
+ *   - for `LV_COLOR_FORMAT_I1`: 0..1
+ *   - for `LV_COLOR_FORMAT_I2`: 0..3
+ *   - for `LV_COLOR_FORMAT_I4`: 0..15
+ *   - for `LV_COLOR_FORMAT_I8`: 0..255
  * @param c the color to set in lv_color32_t format
  */
 void lv_image_buf_set_palette(lv_image_dsc_t * dsc, uint8_t id, lv_color32_t c);
diff --git a/src/draw/lv_image_decoder.h b/src/draw/lv_image_decoder.h
index 329c6e3950..e1112abfb8 100644
--- a/src/draw/lv_image_decoder.h
+++ b/src/draw/lv_image_decoder.h
@@ -198,7 +198,7 @@ lv_result_t lv_image_decoder_get_info(const void * src, lv_image_header_t * head
  *  1) File name: E.g. "S:folder/img1.png" (The drivers needs to registered via `lv_fs_drv_register())`)
  *  2) Variable: Pointer to an `lv_image_dsc_t` variable
  *  3) Symbol: E.g. `LV_SYMBOL_OK`
- * @param color The color of the image with `LV_IMAGE_CF_ALPHA_...`
+ * @param color The color of the image with `LV_COLOR_FORMAT_ALPHA_...`
  * @param args args about how the image should be opened.
  * @return LV_RESULT_OK: opened the image. `dsc->img_data` and `dsc->header` are set.
  *         LV_RESULT_INVALID: none of the registered image decoders were able to open the image.
diff --git a/src/draw/nxp/vglite/lv_draw_vglite_label.c b/src/draw/nxp/vglite/lv_draw_vglite_label.c
index edff907e1b..c28f420d85 100644
--- a/src/draw/nxp/vglite/lv_draw_vglite_label.c
+++ b/src/draw/nxp/vglite/lv_draw_vglite_label.c
@@ -73,7 +73,7 @@ void lv_draw_vglite_label(lv_draw_unit_t * draw_unit, const lv_draw_label_dsc_t
 {
     if(dsc->opa <= LV_OPA_MIN) return;
 
-    lv_draw_label_iterate_letters(draw_unit, dsc, coords, _draw_vglite_letter);
+    lv_draw_label_iterate_characters(draw_unit, dsc, coords, _draw_vglite_letter);
 }
 
 /**********************
diff --git a/src/draw/renesas/dave2d/lv_draw_dave2d_label.c b/src/draw/renesas/dave2d/lv_draw_dave2d_label.c
index d4ac288790..5eea263ca0 100644
--- a/src/draw/renesas/dave2d/lv_draw_dave2d_label.c
+++ b/src/draw/renesas/dave2d/lv_draw_dave2d_label.c
@@ -12,7 +12,7 @@ void lv_draw_dave2d_label(lv_draw_dave2d_unit_t * u, const lv_draw_label_dsc_t *
 
     unit = u;
 
-    lv_draw_label_iterate_letters(&u->base_unit, dsc, coords, lv_draw_dave2d_draw_letter_cb);
+    lv_draw_label_iterate_characters(&u->base_unit, dsc, coords, lv_draw_dave2d_draw_letter_cb);
 
 }
 
diff --git a/src/draw/sw/blend/lv_draw_sw_blend.h b/src/draw/sw/blend/lv_draw_sw_blend.h
index 0124f36e99..eb993585a8 100644
--- a/src/draw/sw/blend/lv_draw_sw_blend.h
+++ b/src/draw/sw/blend/lv_draw_sw_blend.h
@@ -77,7 +77,7 @@ typedef struct {
 
 /**
  * Call the blend function of the `layer`.
- * @param layer      pointer to a draw context
+ * @param draw_unit     pointer to a draw unit
  * @param dsc           pointer to an initialized blend descriptor
  */
 void lv_draw_sw_blend(struct _lv_draw_unit_t * draw_unit, const lv_draw_sw_blend_dsc_t * dsc);
diff --git a/src/draw/sw/lv_draw_sw.h b/src/draw/sw/lv_draw_sw.h
index 8a3a7e1295..0f2a2fd4fa 100644
--- a/src/draw/sw/lv_draw_sw.h
+++ b/src/draw/sw/lv_draw_sw.h
@@ -55,36 +55,119 @@ typedef struct {
  * GLOBAL PROTOTYPES
  **********************/
 
+/**
+ * Initialize the SW renderer. Called in internally.
+ * It creates as many SW renderers as defined in LV_DRAW_SW_DRAW_UNIT_CNT
+ */
 void lv_draw_sw_init(void);
 
+/**
+ * Deinitialize the SW renderers
+ */
 void lv_draw_sw_deinit(void);
 
-LV_ATTRIBUTE_FAST_MEM void lv_draw_sw_image(lv_draw_unit_t * draw_unit, const lv_draw_image_dsc_t * draw_dsc,
-                                            const lv_area_t * coords);
-
+/**
+ * Fill an area using SW render. Handle gradient and radius.
+ * @param draw_unit     pointer to a draw unit
+ * @param dsc           the draw descriptor
+ * @param coords        the coordinates of the rectangle
+ */
 void lv_draw_sw_fill(lv_draw_unit_t * draw_unit, const lv_draw_fill_dsc_t * dsc, const lv_area_t * coords);
 
+/**
+ * Draw border with SW render.
+ * @param draw_unit     pointer to a draw unit
+ * @param dsc           the draw descriptor
+ * @param coords        the coordinates of the rectangle
+ */
 void lv_draw_sw_border(lv_draw_unit_t * draw_unit, const lv_draw_border_dsc_t * dsc, const lv_area_t * coords);
 
+/**
+ * Draw box shadow with SW render.
+ * @param draw_unit     pointer to a draw unit
+ * @param dsc           the draw descriptor
+ * @param coords        the coordinates of the rectangle for which the box shadow should be drawn
+ */
 void lv_draw_sw_box_shadow(lv_draw_unit_t * draw_unit, const lv_draw_box_shadow_dsc_t * dsc, const lv_area_t * coords);
 
+/**
+ * Draw an image with SW render. It handles image decoding, tiling, transformations, and recoloring.
+ * @param draw_unit     pointer to a draw unit
+ * @param dsc           the draw descriptor
+ * @param coords        the coordinates of the image
+ */
+void lv_draw_sw_image(lv_draw_unit_t * draw_unit, const lv_draw_image_dsc_t * draw_dsc,
+                      const lv_area_t * coords);
+
+/**
+ * Draw a label with SW render.
+ * @param draw_unit     pointer to a draw unit
+ * @param dsc           the draw descriptor
+ * @param coords        the coordinates of the label
+ */
 void lv_draw_sw_label(lv_draw_unit_t * draw_unit, const lv_draw_label_dsc_t * dsc, const lv_area_t * coords);
 
+/**
+ * Draw an arc with SW render.
+ * @param draw_unit     pointer to a draw unit
+ * @param dsc           the draw descriptor
+ * @param coords        the coordinates of the arc
+ */
 void lv_draw_sw_arc(lv_draw_unit_t * draw_unit, const lv_draw_arc_dsc_t * dsc, const lv_area_t * coords);
 
-LV_ATTRIBUTE_FAST_MEM void lv_draw_sw_line(lv_draw_unit_t * draw_unit, const lv_draw_line_dsc_t * dsc);
+/**
+ * Draw a line with SW render.
+ * @param draw_unit     pointer to a draw unit
+ * @param dsc           the draw descriptor
+ */
+void lv_draw_sw_line(lv_draw_unit_t * draw_unit, const lv_draw_line_dsc_t * dsc);
 
+/**
+ * Blend a layer with SW render
+ * @param draw_unit     pointer to a draw unit
+ * @param dsc           the draw descriptor
+ * @param coords        the coordinates of the layer
+ */
 void lv_draw_sw_layer(lv_draw_unit_t * draw_unit, const lv_draw_image_dsc_t * draw_dsc, const lv_area_t * coords);
 
+/**
+ * Draw a triangle with SW render.
+ * @param draw_unit     pointer to a draw unit
+ * @param dsc           the draw descriptor
+ */
 void lv_draw_sw_triangle(lv_draw_unit_t * draw_unit, const lv_draw_triangle_dsc_t * dsc);
 
+/**
+ * Mask out a rectangle with radius from a current layer
+ * @param draw_unit     pointer to a draw unit
+ * @param dsc           the draw descriptor
+ * @param coords        the coordinates of the mask
+ */
 void lv_draw_sw_mask_rect(lv_draw_unit_t * draw_unit, const lv_draw_mask_rect_dsc_t * dsc, const lv_area_t * coords);
 
+/**
+ * Used internally to get a transformed are of an image
+ * @param draw_unit     pointer to a draw unit
+ * @param dest_area     the area to calculate, i.e. get this area from the transformed image
+ * @param src_buf       the source buffer
+ * @param src_w         source buffer width in pixels
+ * @param src_h         source buffer height in pixels
+ * @param src_stride    source buffer stride in bytes
+ * @param dsc           the draw descriptor
+ * @param sup           supplementary data
+ * @param cf            color format of the source buffer
+ * @param dest_buf      the destination buffer
+ */
 void lv_draw_sw_transform(lv_draw_unit_t * draw_unit, const lv_area_t * dest_area, const void * src_buf,
                           int32_t src_w, int32_t src_h, int32_t src_stride,
                           const lv_draw_image_dsc_t * draw_dsc, const lv_draw_image_sup_t * sup, lv_color_format_t cf, void * dest_buf);
 
 #if LV_USE_VECTOR_GRAPHIC
+/**
+ * Draw vector graphics with SW render.
+ * @param draw_unit     pointer to a draw unit
+ * @param dsc           the draw descriptor
+ */
 void lv_draw_sw_vector(lv_draw_unit_t * draw_unit, const lv_draw_vector_task_dsc_t * dsc);
 #endif
 
@@ -96,6 +179,17 @@ void lv_draw_sw_vector(lv_draw_unit_t * draw_unit, const lv_draw_vector_task_dsc
  */
 void lv_draw_sw_rgb565_swap(void * buf, int32_t buf_size_px);
 
+/**
+ * Rotate a buffer into an other buffer
+ * @param src           the source buffer
+ * @param dest          the destination buffer
+ * @param src_width     source width in pixels
+ * @param src_height    source height in pixels
+ * @param src_sride     source stride in bytes (number of bytes in a row)
+ * @param dest_stride   destination stride in bytes (number of bytes in a row)
+ * @param rotation      LV_DISPLAY_ROTATION_0/90/180/270
+ * @param color_format  LV_COLOR_FORMAT_RGB565/RGB888/XRGB8888/ARGB8888
+ */
 void lv_draw_sw_rotate(const void * src, void * dest, int32_t src_width, int32_t src_height, int32_t src_sride,
                        int32_t dest_stride, lv_display_rotation_t rotation, lv_color_format_t color_format);
 
diff --git a/src/draw/sw/lv_draw_sw_img.c b/src/draw/sw/lv_draw_sw_img.c
index 0bbc00173e..340ad497f8 100644
--- a/src/draw/sw/lv_draw_sw_img.c
+++ b/src/draw/sw/lv_draw_sw_img.c
@@ -150,8 +150,8 @@ void lv_draw_sw_layer(lv_draw_unit_t * draw_unit, const lv_draw_image_dsc_t * dr
 #endif
 }
 
-LV_ATTRIBUTE_FAST_MEM void lv_draw_sw_image(lv_draw_unit_t * draw_unit, const lv_draw_image_dsc_t * draw_dsc,
-                                            const lv_area_t * coords)
+void lv_draw_sw_image(lv_draw_unit_t * draw_unit, const lv_draw_image_dsc_t * draw_dsc,
+                      const lv_area_t * coords)
 {
     if(!draw_dsc->tile) {
         _lv_draw_image_normal_helper(draw_unit, draw_dsc, coords, img_draw_core);
diff --git a/src/draw/sw/lv_draw_sw_letter.c b/src/draw/sw/lv_draw_sw_letter.c
index 828b635718..72141c7ebb 100644
--- a/src/draw/sw/lv_draw_sw_letter.c
+++ b/src/draw/sw/lv_draw_sw_letter.c
@@ -54,7 +54,7 @@ void lv_draw_sw_label(lv_draw_unit_t * draw_unit, const lv_draw_label_dsc_t * ds
     if(dsc->opa <= LV_OPA_MIN) return;
 
     LV_PROFILER_BEGIN;
-    lv_draw_label_iterate_letters(draw_unit, dsc, coords, draw_letter_cb);
+    lv_draw_label_iterate_characters(draw_unit, dsc, coords, draw_letter_cb);
     LV_PROFILER_END;
 }
 
diff --git a/src/draw/sw/lv_draw_sw_line.c b/src/draw/sw/lv_draw_sw_line.c
index fbc9b802bc..26011f0361 100644
--- a/src/draw/sw/lv_draw_sw_line.c
+++ b/src/draw/sw/lv_draw_sw_line.c
@@ -42,7 +42,7 @@ LV_ATTRIBUTE_FAST_MEM static void draw_line_ver(lv_draw_unit_t * draw_unit, cons
  *   GLOBAL FUNCTIONS
  **********************/
 
-LV_ATTRIBUTE_FAST_MEM void lv_draw_sw_line(lv_draw_unit_t * draw_unit, const lv_draw_line_dsc_t * dsc)
+void lv_draw_sw_line(lv_draw_unit_t * draw_unit, const lv_draw_line_dsc_t * dsc)
 {
     if(dsc->width == 0) return;
     if(dsc->opa <= LV_OPA_MIN) return;
diff --git a/src/misc/lv_color.h b/src/misc/lv_color.h
index ff1ef70b09..5d80352a6a 100644
--- a/src/misc/lv_color.h
+++ b/src/misc/lv_color.h
@@ -164,15 +164,15 @@ typedef uint8_t lv_color_format_t;
 
 /**
  * Get the pixel size of a color format in bits, bpp
- * @param src_cf a color format (`LV_COLOR_FORMAT_...`)
- * @return the pixel size in bits
+ * @param src_cf    a color format (`LV_COLOR_FORMAT_...`)
+ * @return          the pixel size in bits
  */
 uint8_t lv_color_format_get_bpp(lv_color_format_t cf);
 
 /**
  * Get the pixel size of a color format in bytes
- * @param src_cf a color format (`LV_COLOR_FORMAT_...`)
- * @return the pixel size in bytes
+ * @param src_cf    a color format (`LV_COLOR_FORMAT_...`)
+ * @return          the pixel size in bytes
  */
 static inline uint8_t lv_color_format_get_size(lv_color_format_t cf)
 {
@@ -181,8 +181,8 @@ static inline uint8_t lv_color_format_get_size(lv_color_format_t cf)
 
 /**
  * Check if a color format has alpha channel or not
- * @param src_cf a color format (`LV_IMAGE_CF_...`)
- * @return true: has alpha channel; false: doesn't have alpha channel
+ * @param src_cf    a color format (`LV_COLOR_FORMAT_...`)
+ * @return          true: has alpha channel; false: doesn't have alpha channel
  */
 bool lv_color_format_has_alpha(lv_color_format_t src_cf);
 
diff --git a/src/widgets/canvas/lv_canvas.h b/src/widgets/canvas/lv_canvas.h
index 8d51d36475..9e4fc89174 100644
--- a/src/widgets/canvas/lv_canvas.h
+++ b/src/widgets/canvas/lv_canvas.h
@@ -61,7 +61,7 @@ lv_obj_t * lv_canvas_create(lv_obj_t * parent);
  * @param canvas pointer to a canvas object
  * @param w width of the canvas
  * @param h height of the canvas
- * @param cf color format. `LV_IMAGE_CF_...`
+ * @param cf color format. `LV_COLOR_FORMAT...`
  */
 void lv_canvas_set_buffer(lv_obj_t * canvas, void * buf, int32_t w, int32_t h, lv_color_format_t cf);
 
diff --git a/src/widgets/span/lv_span.c b/src/widgets/span/lv_span.c
index 4a445d76c1..48ac19dac9 100644
--- a/src/widgets/span/lv_span.c
+++ b/src/widgets/span/lv_span.c
@@ -1004,7 +1004,7 @@ static void lv_draw_span(lv_obj_t * obj, lv_layer_t * layer)
 
                 if(ellipsis_valid && pos.x + letter_w + pinfo->letter_space > ellipsis_width) {
                     for(int ell = 0; ell < 3; ell++) {
-                        lv_draw_letter(layer, &label_draw_dsc, &pos, '.');
+                        lv_draw_character(layer, &label_draw_dsc, &pos, '.');
                         pos.x = pos.x + dot_letter_w + pinfo->letter_space;
                     }
                     if(pos.x <= ellipsis_width) {
@@ -1013,7 +1013,7 @@ static void lv_draw_span(lv_obj_t * obj, lv_layer_t * layer)
                     break;
                 }
                 else {
-                    lv_draw_letter(layer, &label_draw_dsc, &pos, letter);
+                    lv_draw_character(layer, &label_draw_dsc, &pos, letter);
                     if(letter_w > 0) {
                         pos.x = pos.x + letter_w + pinfo->letter_space;
                     }