[Request] align-text for canvas' api support more alignments

TridentTD · November 13, 2019, 8:50am

When lv_canvas’ obj draw a text,
at current api support only 3 text-alignments.

LV_LABEL_ALIGN_LEFT
LV_LABEL_ALIGN_CENTER
LV_LABEL_ALIGN_RIGHT

But if a developer want to align the text by baseline or other type.
It is not easy to align the text.

I observe from the other library such as TFT_eSPI
in the library TFT_eSPI when draw text to the tft,
it supports many type of text-alignments
as the following link

github.com

Bodmer/TFT_eSPI/blob/master/TFT_eSPI.h#L488-L502


#define TL_DATUM 0 // Top left (default)
#define TC_DATUM 1 // Top centre
#define TR_DATUM 2 // Top right
#define ML_DATUM 3 // Middle left
#define CL_DATUM 3 // Centre left, same as above
#define MC_DATUM 4 // Middle centre
#define CC_DATUM 4 // Centre centre, same as above
#define MR_DATUM 5 // Middle right
#define CR_DATUM 5 // Centre right, same as above
#define BL_DATUM 6 // Bottom left
#define BC_DATUM 7 // Bottom centre
#define BR_DATUM 8 // Bottom right
#define L_BASELINE  9 // Left character baseline (Line the 'A' character would sit on)
#define C_BASELINE 10 // Centre character baseline
#define R_BASELINE 11 // Right character baseline

If lvgl’s lv_canvas or lv_draw_label(..) supports for many text-alignments more than at the current point of any version of lvgl,
it will be convenient for manupulating the text-alignment.

Thank you.

kisvegabor · November 15, 2019, 2:06pm

So do you suggest to replace LV_LABEL_ALIGN_LEFT/RIGHT/CENTER with higher-level alignments which and treat x/y as offset?

Could it be used with other drawings too? E.g. to draw a rectangle to the right top corner.

It’s only my personal opinion but I think with:

x
y
max_w
align

you can easily position the label. Or is there complicated in some situations?

TridentTD · November 15, 2019, 2:29pm

Example.
When a maker want to display a label on a line,
the maker set only

x, y
datum : L_BASELINE, C_BASELINE, R_BASELINE

as the following picture,
line is at y = 120
the maker set only x = 120, y = 120 (center of the screen) and datum = C_BASELINE
capture_00069

Or another example
When a maker want to display number on watch-dial,
he just calculate a rotated point around a pivot point.
and set only the rotated point x, y with MC_DATUM for drawing number on the watch-dial.

capture_00064

kisvegabor · November 17, 2019, 4:22pm

I see, thanks for the examples.

In the case of labels align has a different meaning. It determines the alignment of the lines, similarly to the Left/Center/Right alignment in Office Word.

Do you have an idea about how to handle C_BASELINE with multi-line text?

TridentTD · November 18, 2019, 6:24am

Thank you for meaning of alignment.

C_BASELINE for multi-line text like this way?

situation :
set x, y = (120,120)
if a text is a multi-line text,
the next line is alway x = 120 ?

capture_00070