BidiMode: what changed

Revision 2 to 3. 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		-	~~` For Example`\~~
25		-	~~` in bdLeftToRight:`\~~
26		-	~~` Menu1, Menu2, Menu2`\~~
27		-	~~` in bdRightToLeft: `\~~
28		-	~~` Menu3, Menu2, Menu1`~~
	24	+	```
	25	+	For Example
	26	+	in bdLeftToRight:
	27	+	Menu1, Menu2, Menu2
	28	+	in bdRightToLeft:
	29	+	Menu3, Menu2, Menu1
	30	+	```
29	31
30	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
31	33
32		-	~~` in bdLeftToRight:`\~~
33		-	~~` Word1 Word2 Word2`\~~
34		-	~~` in bdRightToLeft: `\~~
35		-	~~` Word3 Word2 Word1`~~
	34	+	```
	35	+	in bdLeftToRight:
	36	+	Word1 Word2 Word2
	37	+	in bdRightToLeft:
	38	+	Word3 Word2 Word1
	39	+	```
36	40
37	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.
38	42
39	43		For testing purpose I used English word with a symbol to test Right To Left text reading
40	44
41	45		E.g. Word?
42	46
43	47		For special states or for more compatibility with Delphi there are other values (possible? used? handy?)
44	48
45	49		##### bdRightToLeftNoAlign
46	50
47	51		It is Right to Left but not reversed (except the Alignment property), but in Lazarus worked when use FlipControls
48	52
49	53		##### bdRightToLeftReadingOnly
50	54
51	55		It is Right to Left text reading only; scrollbar and alignment do not take effect (??? remain left to right???).
52	56
53	57		### ParentBidiMode
54	58
55	59		If this is True the control inherits the BidiMode value from its parent.
56	60
57	61		### BidiMode for developers
58	62
59	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
60	64
61	65		``` pascal
62	66		function UseRightToLeftAlignment: Boolean; virtual;
63	67		function UseRightToLeftReading: Boolean; virtual;
64	68		function UseRightToLeftScrollBar: Boolean;
65	69		function IsRightToLeft: Boolean;
66	70		```
67	71
68	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.
69	73
70	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.
71	75
72	76		![](/wiki-images/2/24/BidiMode_Sample_1.png)
73	77
74	78		## Add BidiMode support to LCL components
75	79
76	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:
77	81
78	82		1. Standard Controls: it is easy to enable RTL support: just add some flag to switch it to RightToLeft (TEdit, TList, TComboBox, TCheckBox).
79	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.
80	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).
81	85
82	86		### Add BidiMode property to TControl
83	87
84	88		TBidiMode is already declared in Classes
85	89
86	90		``` pascal
87	91		property BiDiMode: TBiDiMode read FBiDiMode write SetBiDiMode stored IsBiDiModeStored;
88	92		property ParentBiDiMode: Boolean read FParentBiDiMode write SetParentBiDiMode default True;
89	93		```
90	94
91	95		BidiMode must not be stored if ParentBidiMode = True
92	96
93	97		``` pascal
94	98		function TControl.IsBiDiModeStored: Boolean;
95	99		begin
96	100		Result := not ParentBiDiMode;
97	101		end;
98	102		```
99	103
100	104		Override BidiMode functions
101	105
102	106		``` pascal
103	107		function IsRightToLeft:Boolean; override;
104	108		function UseRightToLeftAlignment: Boolean; override;
105	109		function UseRightToLeftReading: Boolean; override;
106	110		function UseRightToLeftScrollBar: Boolean; override;
107	111		```
108	112
109	113		BiDiMode property is public and must published in every control need to RightToLeft
110	114
111	115		### Bidi Controls Road Map
112	116
113	117		GTK2 You must build LCL with OPT=-dGTK2 OPT=-dGTK_2_8
114	118
115	119		\| Component \| win32 \| gtk2 \| carbon \| qt \| wince \| cocoa \|
116	120		\|----\|----\|----\|----\|----\|----\|----\|
117	121		\| TForm \| Working \| Working \| Not Implemented \| Not Implemented \| Not Implemented \| Not Implemented \|
118	122		\| TLabel \| Working \| Working \| Not Implemented \| Not Implemented \| Not Implemented \| Not Implemented \|
119	123		\| TButton \| Working \| Partially Implemented \| Not Implemented \| Not Implemented \| Not Implemented \| Not Implemented \|
120	124		\| TEdit \| Working \| Partially Implemented \| Not Implemented \| Not Implemented \| Not Implemented \| Not Implemented \|
121	125		\| TListBox \| Working \| Partially Implemented \| Not Implemented \| Not Implemented \| Not Implemented \| Not Implemented \|
122	126		\| TComboBox \| Working \| Partially Implemented \| Not Implemented \| Not Implemented \| Not Implemented \| Not Implemented \|
123	127		\| TCheckBox \| Working \| Working \| Not Implemented \| Not Implemented \| Not Implemented \| Not Implemented \|
124	128		\| TStaticText \| Working \| Partially Implemented \| Not Implemented \| Not Implemented \| Not Implemented \| Not Implemented \|
125	129		\| TGroupBox \| Working \| Working \| Not Implemented \| Not Implemented \| Not Implemented \| Not Implemented \|
126	130		\| TRadioButton \| Working \| Working \| Not Implemented \| Not Implemented \| Not Implemented \| Not Implemented \|
127	131		\| Menus \| Working \| Working \| Not Implemented \| Not Implemented \| Not Implemented \| Not Implemented \|
128	132		\| TBitBtn \| Partially Implemented \| Working \| Not Implemented \| Not Implemented \| Not Implemented \| Not Implemented \|
129	133		\| TSpeedBtn \| Working \| Working \| Not Implemented \| Not Implemented \| Not Implemented \| Not Implemented \|
130	134		\| TRadioGroup \| Working \| Working \| Not Implemented \| Not Implemented \| Not Implemented \| Not Implemented \|
131	135		\| TCheckGroup \| Working \| Working \| Not Implemented \| Not Implemented \| Not Implemented \| Not Implemented \|
132	136		\| TGrid \| Working \| Partially Implemented \| Not Implemented \| Not Implemented \| Not Implemented \| Not Implemented \|
133	137
134	138		### Functions and Utils useful for multi language application
135	139
136		-	~~` ``TControl.FlipControls; virtual`\~~
137		-	~~` Change Right to Left and Left to Right in this properties (Left, Align, Anchors and Alignment)`~~
	140	+	```
	141	+	TControl.FlipControls; virtual
	142	+	Change Right to Left and Left to Right in this properties (Left, Align, Anchors and Alignment)
	143	+	```
138	144
139	145		## How to test RightToLeft reading
140	146
141	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.
142	148
143	149		# BiDi support of the widgetsets
144	150
145	151		## Carbon
146	152
147	153		Write me.
148	154
149	155		## fpGui
150	156
151	157		Write me.
152	158
153	159		## Gtk1
154	160
155	161		Has almost no BiDi support. Is deprecated by Lazarus anyway, so no new development at all.
156	162
157	163		## Gtk2
158	164
159	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.
160	166
161	167		## Qt
162	168
163	169		Write me.
164	170
165	171		## Windows
166	172
167	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.
168	174
169	175		# References
170	176
171	177		- [Unicode Bidirectional Algorithm](http://www.unicode.org/reports/tr9/)
172	178		- [Design and Implementation of a Win32 Text Editor](http://www.catch22.net/book/export/html/14)
173	179
174	180		---
175	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).
176	182		Category: LCL
177	183		Category: Lazarus
178	184		Category: Lazarus internals
179	185		Category: Localization

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