BidiMode: what changed

Revision 3 to 4. Removed lines have a minus sign; added lines have a plus sign.

Old	New		Line
1	1		Some languages (Arabic, Hebrew, Farsi ...) write the characters from the right to the left, and adequate support for this must be implemented on Lazarus.
2	2
3	3		#### BidiMode
4	4
5	5		BidiMode can have these settings:
6	6
7	7		``` pascal
8	8		bdLeftToRight
9	9		bdRightToLeft
10	10		bdRightToLeftNoAlign
11	11		bdRightToLeftReadingOnly
12	12		```
13	13
14	14		##### bdLeftToRight
15	15
16	16		Default of BidiMode, which means read and order is normal "Left To Right"
17	17
18	18		##### bdRightToLeft
19	19
20	20		Makes a control Right To Left reading text and right alignment depend a kind of the control,
21	21
22	22		In Delphi if there is Alignment property effect by reverse taLeft to taRight and vise versa, but in Lazarus we will reverse the alignment with FlipControls function, which is more consistent with Anchors and Align properties. Also bdRightToLeft takes a Scrollbar at the left and if there is a cell or menus they must ordered from the right.
23	23
24		-	~~```~~
	24	+	```text
25	25		For Example
26	26		in bdLeftToRight:
27	27		Menu1, Menu2, Menu2
28	28		in bdRightToLeft:
29	29		Menu3, Menu2, Menu1
30	30		```
31	31
32	32		That means not just Right Alignment; it is Right To Left Order. bdRightToLeft must effect the text reading as depend on the OS if it is supported, the sentence words take as like Cells
33	33
34		-	~~```~~
	34	+	```text
35	35		in bdLeftToRight:
36	36		Word1 Word2 Word2
37	37		in bdRightToLeft:
38	38		Word3 Word2 Word1
39	39		```
40	40
41	41		We are reading the Word1 first then Word2, We read from the Right to Left, but Draw Text is more complicated than normal Cells; in fact the function that draws the text cares about English/Latin words and draws it Left To Right, so if we mixed both languages in the same sentence, the draw function draws continual English words in Left To Right order to make it readable, but symbols like ? or ! are considered as Right To Left characters.
42	42
43	43		For testing purpose I used English word with a symbol to test Right To Left text reading
44	44
45	45		E.g. Word?
46	46
47	47		For special states or for more compatibility with Delphi there are other values (possible? used? handy?)
48	48
49	49		##### bdRightToLeftNoAlign
50	50
51	51		It is Right to Left but not reversed (except the Alignment property), but in Lazarus worked when use FlipControls
52	52
53	53		##### bdRightToLeftReadingOnly
54	54
55	55		It is Right to Left text reading only; scrollbar and alignment do not take effect (??? remain left to right???).
56	56
57	57		### ParentBidiMode
58	58
59	59		If this is True the control inherits the BidiMode value from its parent.
60	60
61	61		### BidiMode for developers
62	62
63	63		When you build you own controls and try to make your control support Right to Left or BidiMode, you must not access the BiDiMode property directly. Instead you must use
64	64
65	65		``` pascal
66	66		function UseRightToLeftAlignment: Boolean; virtual;
67	67		function UseRightToLeftReading: Boolean; virtual;
68	68		function UseRightToLeftScrollBar: Boolean;
69	69		function IsRightToLeft: Boolean;
70	70		```
71	71
72	72		Because some controls do not need to make changes to the alignment - for example TButton it always is centered, or TMainMenu which always is right aligned if it is Right to Left.
73	73
74	74		Not just reading the words and cells, everything depends on the order (positions). For an application there is a Menus and Controls that when placed on the form must have positions starting from the right. It is like looking at a LeftToRight Form in a mirror. The flow of the Form must be from Right To Left.
75	75
76	76		![](/wiki-images/2/24/BidiMode_Sample_1.png)
77	77
78	78		## Add BidiMode support to LCL components
79	79
80	80		Most OSes now support RightToLeft but there are controls that are not supported yet or there is controls made by native language (custom drawn?) such as (TLabel, TGrid). So we have 3 kinds of control:
81	81
82	82		1. Standard Controls: it is easy to enable RTL support: just add some flag to switch it to RightToLeft (TEdit, TList, TComboBox, TCheckBox).
83	83		2. Standard Controls not supported by the OS: There is no idea just waiting the OS developers to implement it to support (TListView, TTreeView), or use native controls that already support it.
84	84		3. Native Controls: hard work is needed to make it Support RightToLeft, or we must add new controls that already have this features (TLabel, TGrid).
85	85
86	86		### Add BidiMode property to TControl
87	87
88	88		TBidiMode is already declared in Classes
89	89
90	90		``` pascal
91	91		property BiDiMode: TBiDiMode read FBiDiMode write SetBiDiMode stored IsBiDiModeStored;
92	92		property ParentBiDiMode: Boolean read FParentBiDiMode write SetParentBiDiMode default True;
93	93		```
94	94
95	95		BidiMode must not be stored if ParentBidiMode = True
96	96
97	97		``` pascal
98	98		function TControl.IsBiDiModeStored: Boolean;
99	99		begin
100	100		Result := not ParentBiDiMode;
101	101		end;
102	102		```
103	103
104	104		Override BidiMode functions
105	105
106	106		``` pascal
107	107		function IsRightToLeft:Boolean; override;
108	108		function UseRightToLeftAlignment: Boolean; override;
109	109		function UseRightToLeftReading: Boolean; override;
110	110		function UseRightToLeftScrollBar: Boolean; override;
111	111		```
112	112
113	113		BiDiMode property is public and must published in every control need to RightToLeft
114	114
115	115		### Bidi Controls Road Map
116	116
117	117		GTK2 You must build LCL with OPT=-dGTK2 OPT=-dGTK_2_8
118	118
119	119		\| Component \| win32 \| gtk2 \| carbon \| qt \| wince \| cocoa \|
120	120		\|----\|----\|----\|----\|----\|----\|----\|
121	121		\| TForm \| Working \| Working \| Not Implemented \| Not Implemented \| Not Implemented \| Not Implemented \|
122	122		\| TLabel \| Working \| Working \| Not Implemented \| Not Implemented \| Not Implemented \| Not Implemented \|
123	123		\| TButton \| Working \| Partially Implemented \| Not Implemented \| Not Implemented \| Not Implemented \| Not Implemented \|
124	124		\| TEdit \| Working \| Partially Implemented \| Not Implemented \| Not Implemented \| Not Implemented \| Not Implemented \|
125	125		\| TListBox \| Working \| Partially Implemented \| Not Implemented \| Not Implemented \| Not Implemented \| Not Implemented \|
126	126		\| TComboBox \| Working \| Partially Implemented \| Not Implemented \| Not Implemented \| Not Implemented \| Not Implemented \|
127	127		\| TCheckBox \| Working \| Working \| Not Implemented \| Not Implemented \| Not Implemented \| Not Implemented \|
128	128		\| TStaticText \| Working \| Partially Implemented \| Not Implemented \| Not Implemented \| Not Implemented \| Not Implemented \|
129	129		\| TGroupBox \| Working \| Working \| Not Implemented \| Not Implemented \| Not Implemented \| Not Implemented \|
130	130		\| TRadioButton \| Working \| Working \| Not Implemented \| Not Implemented \| Not Implemented \| Not Implemented \|
131	131		\| Menus \| Working \| Working \| Not Implemented \| Not Implemented \| Not Implemented \| Not Implemented \|
132	132		\| TBitBtn \| Partially Implemented \| Working \| Not Implemented \| Not Implemented \| Not Implemented \| Not Implemented \|
133	133		\| TSpeedBtn \| Working \| Working \| Not Implemented \| Not Implemented \| Not Implemented \| Not Implemented \|
134	134		\| TRadioGroup \| Working \| Working \| Not Implemented \| Not Implemented \| Not Implemented \| Not Implemented \|
135	135		\| TCheckGroup \| Working \| Working \| Not Implemented \| Not Implemented \| Not Implemented \| Not Implemented \|
136	136		\| TGrid \| Working \| Partially Implemented \| Not Implemented \| Not Implemented \| Not Implemented \| Not Implemented \|
137	137
138	138		### Functions and Utils useful for multi language application
139	139
140		-	~~```~~
	140	+	```text
141	141		TControl.FlipControls; virtual
142	142		Change Right to Left and Left to Right in this properties (Left, Align, Anchors and Alignment)
143	143		```
144	144
145	145		## How to test RightToLeft reading
146	146
147	147		Create a new form, then add a TButton or TEdit. Set the caption to OK?. You must add ? or ! or . to the last word without a space. Now set the BidiMode to bdRightToLeft, and you should see the ? in the left of word if it works.
148	148
149	149		# BiDi support of the widgetsets
150	150
151	151		## Carbon
152	152
153	153		Write me.
154	154
155	155		## fpGui
156	156
157	157		Write me.
158	158
159	159		## Gtk1
160	160
161	161		Has almost no BiDi support. Is deprecated by Lazarus anyway, so no new development at all.
162	162
163	163		## Gtk2
164	164
165	165		In TMemo, TEdit, TComboBox the popup menu contains the two sub menus Input Methods and Insert Unicode Control character. Gtk2 uses for text rendering the Pango library, which has excellent Unicode support.
166	166
167	167		## Qt
168	168
169	169		Write me.
170	170
171	171		## Windows
172	172
173	173		In Windows 7 you can switch in TMemo, TEdit, TComboBox the base direction with Left-`Ctrl`+Right-`Shift` to RTL (right to left) and Right-`Ctrl`+Left-`Shift` to LTR (left to right). This also works in the IDE for most things, like in the Property Editor and the Strings Editor Dialog.
174	174
175	175		# References
176	176
177	177		- [Unicode Bidirectional Algorithm](http://www.unicode.org/reports/tr9/)
178	178		- [Design and Implementation of a Win32 Text Editor](http://www.catch22.net/book/export/html/14)
179	179
180	180		---
181	181		From the Free Pascal wiki, page "BidiMode", as it stood on 2020-02-07 after a change by Trev, out of the wiki's dump of 2024-05-26. Copyright stays with the author who wrote it, according to the old wiki's [[Licensing]] page. If you have concerns about this material, [message the admin](/wiki-contact).
182	182		Category: LCL
183	183		Category: Lazarus
184	184		Category: Lazarus internals
185	185		Category: Localization

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