BidiMode: what changed

Revision 1 to 2. 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		` For Example`\
25	25		` in bdLeftToRight:`\
26	26		` Menu1, Menu2, Menu2`\
27	27		` in bdRightToLeft: `\
28	28		` Menu3, Menu2, Menu1`
29	29
30	30		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	31
32	32		` in bdLeftToRight:`\
33	33		` Word1 Word2 Word2`\
34	34		` in bdRightToLeft: `\
35	35		` Word3 Word2 Word1`
36	36
37	37		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	38
39	39		For testing purpose I used English word with a symbol to test Right To Left text reading
40	40
41	41		E.g. Word?
42	42
43	43		For special states or for more compatibility with Delphi there are other values (possible? used? handy?)
44	44
45	45		##### bdRightToLeftNoAlign
46	46
47	47		It is Right to Left but not reversed (except the Alignment property), but in Lazarus worked when use FlipControls
48	48
49	49		##### bdRightToLeftReadingOnly
50	50
51	51		It is Right to Left text reading only; scrollbar and alignment do not take effect (??? remain left to right???).
52	52
53	53		### ParentBidiMode
54	54
55	55		If this is True the control inherits the BidiMode value from its parent.
56	56
57	57		### BidiMode for developers
58	58
59	59		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	60
61	61		``` pascal
62	62		function UseRightToLeftAlignment: Boolean; virtual;
63	63		function UseRightToLeftReading: Boolean; virtual;
64	64		function UseRightToLeftScrollBar: Boolean;
65	65		function IsRightToLeft: Boolean;
66	66		```
67	67
68	68		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	69
70	70		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	71
72		-	~~<figure>~~
73		-	~~<img src="BidiMode_Sample_1.png" title="Sample 1" />~~
74		-	~~<figcaption>Sample 1</figcaption>~~
75		-	~~</figure>~~
	72	+	![](/wiki-images/2/24/BidiMode_Sample_1.png)
76	73
77	74		## Add BidiMode support to LCL components
78	75
79	76		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:
80	77
81	78		1. Standard Controls: it is easy to enable RTL support: just add some flag to switch it to RightToLeft (TEdit, TList, TComboBox, TCheckBox).
82	79		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.
83	80		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).
84	81
85	82		### Add BidiMode property to TControl
86	83
87	84		TBidiMode is already declared in Classes
88	85
89	86		``` pascal
90	87		property BiDiMode: TBiDiMode read FBiDiMode write SetBiDiMode stored IsBiDiModeStored;
91	88		property ParentBiDiMode: Boolean read FParentBiDiMode write SetParentBiDiMode default True;
92	89		```
93	90
94	91		BidiMode must not be stored if ParentBidiMode = True
95	92
96	93		``` pascal
97	94		function TControl.IsBiDiModeStored: Boolean;
98	95		begin
99	96		Result := not ParentBiDiMode;
100	97		end;
101	98		```
102	99
103	100		Override BidiMode functions
104	101
105	102		``` pascal
106	103		function IsRightToLeft:Boolean; override;
107	104		function UseRightToLeftAlignment: Boolean; override;
108	105		function UseRightToLeftReading: Boolean; override;
109	106		function UseRightToLeftScrollBar: Boolean; override;
110	107		```
111	108
112	109		BiDiMode property is public and must published in every control need to RightToLeft
113	110
114	111		### Bidi Controls Road Map
115	112
116	113		GTK2 You must build LCL with OPT=-dGTK2 OPT=-dGTK_2_8
117	114
118	115		\| Component \| win32 \| gtk2 \| carbon \| qt \| wince \| cocoa \|
119	116		\|----\|----\|----\|----\|----\|----\|----\|
120	117		\| TForm \| Working \| Working \| Not Implemented \| Not Implemented \| Not Implemented \| Not Implemented \|
121	118		\| TLabel \| Working \| Working \| Not Implemented \| Not Implemented \| Not Implemented \| Not Implemented \|
122	119		\| TButton \| Working \| Partially Implemented \| Not Implemented \| Not Implemented \| Not Implemented \| Not Implemented \|
123	120		\| TEdit \| Working \| Partially Implemented \| Not Implemented \| Not Implemented \| Not Implemented \| Not Implemented \|
124	121		\| TListBox \| Working \| Partially Implemented \| Not Implemented \| Not Implemented \| Not Implemented \| Not Implemented \|
125	122		\| TComboBox \| Working \| Partially Implemented \| Not Implemented \| Not Implemented \| Not Implemented \| Not Implemented \|
126	123		\| TCheckBox \| Working \| Working \| Not Implemented \| Not Implemented \| Not Implemented \| Not Implemented \|
127	124		\| TStaticText \| Working \| Partially Implemented \| Not Implemented \| Not Implemented \| Not Implemented \| Not Implemented \|
128	125		\| TGroupBox \| Working \| Working \| Not Implemented \| Not Implemented \| Not Implemented \| Not Implemented \|
129	126		\| TRadioButton \| Working \| Working \| Not Implemented \| Not Implemented \| Not Implemented \| Not Implemented \|
130	127		\| Menus \| Working \| Working \| Not Implemented \| Not Implemented \| Not Implemented \| Not Implemented \|
131	128		\| TBitBtn \| Partially Implemented \| Working \| Not Implemented \| Not Implemented \| Not Implemented \| Not Implemented \|
132	129		\| TSpeedBtn \| Working \| Working \| Not Implemented \| Not Implemented \| Not Implemented \| Not Implemented \|
133	130		\| TRadioGroup \| Working \| Working \| Not Implemented \| Not Implemented \| Not Implemented \| Not Implemented \|
134	131		\| TCheckGroup \| Working \| Working \| Not Implemented \| Not Implemented \| Not Implemented \| Not Implemented \|
135	132		\| TGrid \| Working \| Partially Implemented \| Not Implemented \| Not Implemented \| Not Implemented \| Not Implemented \|
136	133
137	134		### Functions and Utils useful for multi language application
138	135
139	136		` ``TControl.FlipControls; virtual`\
140	137		` Change Right to Left and Left to Right in this properties (Left, Align, Anchors and Alignment)`
141	138
142	139		## How to test RightToLeft reading
143	140
144	141		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.
145	142
146	143		# BiDi support of the widgetsets
147	144
148	145		## Carbon
149	146
150	147		Write me.
151	148
152	149		## fpGui
153	150
154	151		Write me.
155	152
156	153		## Gtk1
157	154
158	155		Has almost no BiDi support. Is deprecated by Lazarus anyway, so no new development at all.
159	156
160	157		## Gtk2
161	158
162	159		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.
163	160
164	161		## Qt
165	162
166	163		Write me.
167	164
168	165		## Windows
169	166
170		-	In Windows 7 you can switch in TMemo, TEdit, TComboBox the base direction with Left-<span class="kbd">Ctrl</span>+Right-<span class="kbd">Shift</span> to RTL (right to left) and Right-<span class="kbd">Ctrl</span>+Left-<span class="kbd">Shift</span> to LTR (left to right). This also works in the IDE for most things, like in the Property Editor and the Strings Editor Dialog.
	167	+	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.
171	168
172	169		# References
173	170
174	171		- [Unicode Bidirectional Algorithm](http://www.unicode.org/reports/tr9/)
175	172		- [Design and Implementation of a Win32 Text Editor](http://www.catch22.net/book/export/html/14)
176	173
177	174		---
178	175		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).
179	176		Category: LCL
180	177		Category: Lazarus
181	178		Category: Lazarus internals
182	179		Category: Localization

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