一、概述
最近看到网上有人问怎么用C语言实现屏幕截图，刚好自己也在研究Linux驱动，于是花了半天时间把Linux的FrameBuffer驱动看懂了个七八，接着就动手写了个LCD屏幕截图的应用程序。
一些说明：
1. 板子LCD的分辨率为480x272，像素格式为RGB565。
2. 程序首先获取LCD的一些参数 ，然后将获取到的一帧数据转换为RGB24格式，最后用jpeglib库压缩为jpg格式的图片。
3. 在嵌入式Linux的板子上测试通过。
二、实现
程序中有注释，不多说，直接上程序：
1 #include
2 #include
3 #include
4 #include
5 #include
6 #include
7
8 #include
9
10 #include
11 #include
12
13
14 /*RGB565转RGB24函数
15 *@rgb565: 指向存放rgb565数据的起始地址
16 *@rgb24：指向存放rgb24数据的起始地址
17 *@width：屏幕（分辨率）的宽度
18 *@height：屏幕（分辨率）的高度
19 */
20 int RGB565_to_RGB24(unsigned char *rgb565,unsigned char *rgb24,int width,int height)
21 {
22 int i;
23 int whole = width*height;
24 unsigned char r,g,b;
25 unsigned short int *pix565;
26
27 pix565 = (unsigned short int *)rgb565;
28
29 for(i = 0;i < whole;i++)
30 {
31 r = ((*pix565)>>11)&0x1f;
32 *rgb24 = (r<<3) | (r>>2);
33 rgb24++;
34 g = ((*pix565)>>5)&0x3f;
35 *rgb24 = (g<<2) | (g>>4);
36 rgb24++;
37 b = (*pix565)&0x1f;
38 *rgb24 = (b<<3) | (b>>2);
39 rgb24++;
40 pix565++;
41
42 }
43 return 1;
44 }
45
46 /*jpeg压缩函数
47 *@rgb：指向存放rgb24数据的起始地址
48 *@width：屏幕（分辨率）的宽度
49 *@height：屏幕（分辨率）的高度
50 */
51 int jpeg_compress(unsigned char *rgb,int width,int height)
52 {
53 struct jpeg_compress_struct cinfo;
54 struct jpeg_error_mgr jerr;
55 FILE * outfile;
56 JSAMPROW row_pointer[1];
57 int row_stride;
58 cinfo.err = jpeg_std_error(&jerr);
59 jpeg_create_compress(&cinfo);
60 //输出文件名为：out.jpg
61 if ((outfile = fopen("out.jpg", "wb")) == NULL)
62 {
63 printf("can not open out.jpg\n");
64 return -1;
65 }
66 jpeg_stdio_dest(&cinfo, outfile);
67
68 cinfo.image_width = width;
69 cinfo.image_height = height;
70 cinfo.input_components = 3;
71 //输入数据格式为RGB
72 cinfo.in_color_space = JCS_RGB;
73
74 jpeg_set_defaults(&cinfo);
75 //压缩质量为80
76 jpeg_set_quality(&cinfo, 80, TRUE );
77 jpeg_start_compress(&cinfo, TRUE);
78 row_stride = width * 3;
79
80 while (cinfo.next_scanline < cinfo.image_height)
81 {
82 row_pointer[0] = &rgb[cinfo.next_scanline * row_stride];
83 (void) jpeg_write_scanlines(&cinfo, row_pointer, 1);
84 }
85
86 jpeg_finish_compress(&cinfo);
87 fclose(outfile);
88
89 jpeg_destroy_compress(&cinfo);
90
91 return 1;
92 }
93
94
95 int main()
96 {
97
98 int fd;
99 struct fb_var_screeninfo fb_var_info;
100 struct fb_fix_screeninfo fb_fix_info;
101 unsigned char *trgb;
102 unsigned char *rgb;
103 int buffer_size;
104
105 //打开framebuffer设备
106 fd = open("/dev/fb0",O_RDONLY);
107 if(fd < 0)
108 {
109 printf("can not open dev\n");
110 exit(1);
111 }
112
113 //获取LCD的可变参数
114 ioctl(fd,FBIOGET_VSCREENINFO,&fb_var_info);
115 //一个像素多少位
116 printf("bits_per_pixel: %d\n",fb_var_info.bits_per_pixel);
117 //x分辨率
118 printf("xres: %d\n",fb_var_info.xres);
119 //y分辨率
120 printf("yres: %d\n",fb_var_info.yres);
121 //r分量长度（bit）
122 printf("red_length: %d\n",fb_var_info.red.length);
123 //g分量长度（bit）
124 printf("green_length: %d\n",fb_var_info.green.length);
125 //b分量长度（bit）
126 printf("blue_length: %d\n",fb_var_info.blue.length);
127 //t(透明度)分量长度（bit）
128 printf("transp_length: %d\n",fb_var_info.transp.length);
129 //r分量偏移
130 printf("red_offset: %d\n",fb_var_info.red.offset);
131 //g分量偏移
132 printf("green_offset: %d\n",fb_var_info.green.offset);
133 //b分量偏移
134 printf("blue_offset: %d\n",fb_var_info.blue.offset);
135 //t分量偏移
136 printf("transp_offset: %d\n",fb_var_info.transp.offset);
137
138 //获取LCD的固定参数
139 ioctl(fd,FBIOGET_FSCREENINFO,&fb_fix_info);
140 //一帧大小
141 printf("smem_len: %d\n",fb_fix_info.smem_len);
142 //一行大小
143 printf("line_length: %d\n",fb_fix_info.line_length);
144
145 //一帧大小
146 buffer_size = (fb_var_info.xres * fb_var_info.yres * fb_var_info.bits_per_pixel/8);
147
148 trgb = (unsigned char *)malloc(buffer_size);
149 if(trgb==NULL)
150 exit(0);
151 rgb = (unsigned char *)malloc(fb_var_info.xres * fb_var_info.yres * 3);
152 if(rgb==NULL)
153 {
154 goto here;
155 }
156 //获取一帧数据
157 if(read(fd,trgb,buffer_size) < 0)
158 {
159 printf("reaf failed!\n");
160 goto read_fail;
161 }
162 //格式转换
163 RGB565_to_RGB24(trgb,rgb,fb_var_info.xres,fb_var_info.yres);
164 //jpeg压缩
165 if(jpeg_compress(rgb,fb_var_info.xres,fb_var_info.yres)<0)
166 printf("compress failed!\n");
167
168 read_fail:
169 free(rgb);
170 here:
171 free(trgb);
172
173
174 close(fd);
175
176 return 0;
177 }
效果：
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