BGRABitmap and OpenGL: what changed

Revision 1 to 2. Removed lines have a minus sign; added lines have a plus sign.

Old	New		Line
1	1		[[BGRABitmap]] allows to draw with [[OpenGL]] and so to benefit from hardware acceleration.
2	2
3	3		### OpenGL surface
4	4
5	5		You will need an OpenGL surface. The package LazOpenGLContext in the directory components\opengl of lazarus supplies this surface. It is necessary to add some code to handle it properly. The control TBGLVirtualScreen is here to make it easy for you. Note that it relies on LazOpenGLContext so you will need to install this package anyway.
6	6
7	7		The installation of the package on Linux can be problematic. See below the Linux note before installing the package.
8	8
9	9		#### TBGLVirtualScreen
10	10
11	11		The package BGLControls in the archive of [[BGRABitmap]] contains the component TBGLVirtualScreen that supplies an easy-to-use OpenGL surface via [TBGLContext](https://bgrabitmap.github.io/doc/BGRAOpenGL.TBGLContext.html) class. It is recommended to install it as well.
12	12
13	13		It appears in the component toolbar, in the OpenGL tab. You just need to put it on the form and to redefine the Redraw event. For example to draw a red rectangle:
14	14
15	15		``` pascal
16	16		uses
17	17		BGRABitmapTypes;
18	18
19	19		procedure TForm1.BGLVirtualScreen1Redraw(Sender: TObject; BGLContext: TBGLContext);
20	20		begin
21	21		BGLContext.Canvas.FillRect(10, 10, 100, 100, CSSRed);
22	22		end;
23	23		```
24	24
25	25		#### Using only TOpenGLControl
26	26
27	27		In the tab OpenGL you will find TOpenGLControl. Add it to the form and set the property `AutoResizeViewPort` to `true`.
28	28
29	29		In the Paint event:
30	30
31	31		``` pascal
32	32		uses BGRAOpenGL, BGRABitmapTypes;
33	33
34	34		procedure TForm1.OpenGLControl1Paint(Sender: TObject);
35	35		begin
36	36		BGLViewPort(OpenGLControl1.Width, OpenGLControl1.Height, BGRAWhite);
37	37
38	38		// do you drawing here
39	39		BGLCanvas.FillRect(10, 10, 100, 100, CSSRed);
40	40
41	41		OpenGLControl1.SwapBuffers;
42	42		end;
43	43		```
44	44
45	45		You will get:
46	46
47		-	~~<figure>~~
48		-	~~<img src="bgrabitmap-openglcontrol-example1.png" title="bgrabitmap-openglcontrol-example1.png" />~~
49		-	~~<figcaption>bgrabitmap-openglcontrol-example1.png</figcaption>~~
50		-	~~</figure>~~
	47	+	![](/wiki-images/4/41/Bgrabitmap-openglcontrol-example1.png)
51	48
52	49		#### Note on Linux
53	50
54	51		On Linux, it is possible that the [[OpenGL]] library be missing, which prevents the final compilation linking step. To solve the problem, do the following:Pour résoudre le problème, effectuez:
55	52
56	53		``` bash
57	54		#install library
58	55		sudo apt-get install libgl-dev
59	56		#in some cases, add a link to the library (for 64bits processors)
60	57		sudo ln -s /usr/lib/x86_64-linux-gnu/mesa/libGL.so.1 /usr/lib/libGL.so
61	58		sudo ln -s /usr/lib/x86_64-linux-gnu/libglib-2.0.so /usr/lib/libglib-2.0.so
62	59		sudo ln -s /usr/lib/x86_64-linux-gnu/llibgthread-2.0.so /usr/lib/libgthread-2.0.so
63	60		sudo ln -s /usr/lib/x86_64-linux-gnu/libgmodule-2.0.so /usr/lib/libgmodule-2.0.so
64	61		sudo ln -s /usr/lib/x86_64-linux-gnu/libgobject-2.0.so /usr/lib/libgobject-2.0.so
65	62		```
66	63
67	64		After checking the package to install, clicking Yes directly may not work. Instead you can go to Tools and configure Lazarus build. Check the option to do a full clean compilation. From there compile the IDE.
68	65
69	66		When recompiling Lazarus, the program may be stuck on the slashscreen. In that case, terminate the process with the system monitor.
70	67
71	68		### Textures
72	69
73	70		[[OpenGL]] uses its own memory to store images. Moreover it is necessary to be in the right OpenGL context. So load images within the OnPaint event or use LoadTextures and UnloadTextures events of TBGLVirtualScreen. You can also use the fonction UseContext.
74	71
75	72		Textures are stored in a IBGLTexture variable. You can load a texture directly from a file:
76	73
77	74		``` pascal
78	75		uses
79	76		BGRAOpenGL;
80	77
81	78		var
82	79		tex: IBGLTexture;
83	80
84	81		begin
85	82		tex := BGLTexture(path);
86	83		...
87	84		```
88	85
89	86		To free it, simply do:
90	87
91	88		``` pascal
92	89		tex := nil;
93	90		```
94	91
95	92		### Creating textures
96	93
97	94		Instead of using TBGRABitmap class, use [TBGLBitmap class](https://bgrabitmap.github.io/doc/BGRAOpenGL.TBGLBitmap.html) of [BGRAOpenGL unit](https://bgrabitmap.github.io/doc/BGRAOpenGL.html). It is similar in all respect except that it has a Texture property that can be used with OpenGL functions.
98	95
99	96		Finally, if you have finished your drawing and will not modify it anymore, you can free the TBGLBitmap object and retrieve the texture with MakeTextureAndFree function.
100	97
101	98		``` pascal
102	99		uses
103	100		BGRAOpenGL, BGRABitmapTypes;
104	101
105	102		var
106	103		bmp: TBGLBitmap;
107	104		tex: IBGLTexture;
108	105
109	106		begin
110	107		bmp := TBGLBitmap.Create(path);
111	108		bmp.Rectangle(0, 0, bmp.Width, bmp.Height, CSSRed, dmSet);
112	109		tex := bmp.MakeTextureAndFree;
113	110		...
114	111		```
115	112
116	113		### Examples
117	114
118	115		You will find examples in the directory test/test4lcl_opengl[1](https://github.com/bgrabitmap/bgrabitmap/tree/master/test/test4lcl_opengl).
119	116
120	117		#### Probability
121	118
122	119		There is also a demo called probability[2](https://github.com/bgrabitmap/bgracontest/tree/master/2015/probability) in BGRAContext 2015 repository.
123	120
124		-	~~<figure>~~
125		-	~~<img src="probability-screenshot.png" title="probability-screenshot.png" />~~
126		-	~~<figcaption>probability-screenshot.png</figcaption>~~
127		-	~~</figure>~~
	121	+	![](/wiki-images/6/6d/Probability-screenshot.png)
128	122
129	123		---
130	124		From the Free Pascal wiki, page "BGRABitmap and OpenGL", as it stood on 2024-04-03 after a change by Circular, 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).

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