写了个BMP接口函数，方便编写说明书用。

发布于 2012-06-29 11:10:08 浏览：2996 订阅该版

因为要编写说明书，所以写了个BMP抓图接口函数，或许对其他人也有用。
在image_bmp.c中加入一个函数：
```c
void rtgui_image_bmp_header_cfg(struct rtgui_image_bmp_header *bhr, rt_int32_t w, rt_int32_t h, rt_uint16_t bits_per_pixel)
{
	int image_size = w * h * bits_per_pixel/8;
	int header_size = sizeof(struct rtgui_image_bmp_header);

bhr->magic[0] = 'B';
	bhr->magic[1] = 'M';
	bhr->bfSize = header_size + image_size; /* data size */
	bhr->bfReserved1 = 0;
	bhr->bfReserved2 = 0;
	bhr->bfOffBits = header_size;

bhr->biSize = 40; /* sizeof BITMAPINFOHEADER */
	bhr->biWidth = w;
	bhr->biHeight = h;
	bhr->biPlanes = 1;
	bhr->biBitCount = bits_per_pixel;
	bhr->biCompression = BI_BITFIELDS;
	bhr->biSizeImage = image_size;
	bhr->biXPelsPerMeter = 0;
	bhr->biYPelsPerMeter = 0;
	bhr->biClrUsed = 0;
	bhr->biClrImportant = 0;
	if(bhr->biBitCount == 16 && bhr->biCompression == BI_BITFIELDS)
	{
		bhr->bfSize += 12;
		bhr->bfOffBits += 12;
	}
}
```

应用时如下，
```c
//#define BGR_CONVERT_TO_RGB

static void bmp_create(const char *filename)
{
	int fd, w, h, i, pitch;
	rt_uint16_t *src;
	rt_uint32_t mask;
	struct rtgui_image_bmp_header bhr;
	struct rtgui_graphic_driver* grp = rtgui_graphic_driver_get_default();
#ifdef BGR_CONVERT_TO_RGB
	int j;
	rt_uint16_t *line_buf;
	rt_uint16_t color,tmp;
#endif
int tick = rt_tick_get();	
	fd = open(filename, O_WRONLY | O_CREAT, 0);	
	if (fd < 0) 
	{
		rt_kprintf("create file failed
");
		return;
	}

w = grp->width;
	h = grp->height;

pitch = w * sizeof(rt_uint16_t);
#ifdef BGR_CONVERT_TO_RGB
	line_buf = rt_malloc(pitch);
	if (line_buf == RT_NULL)
	{
		rt_kprintf("no memory!
");
		return;
	}
#endif
	rtgui_image_bmp_header_cfg(&bhr, w, h, grp->bits_per_pixel);

write(fd, &bhr, sizeof(struct rtgui_image_bmp_header));

if(bhr.biCompression == BI_BITFIELDS)
	{
		mask = 0xF800;  //Red Mask
		write(fd, &mask, 4);
		mask = 0x07E0;  //Green Mask
		write(fd, &mask, 4);
		mask = 0x001F;  //Blue Mask
		write(fd, &mask, 4);
	}

src = (rt_uint16_t*)grp->framebuffer;
	src += w*h;
	for(i=0; i<h; i++)
	{
		src -= w;
#ifdef BGR_CONVERT_TO_RGB
		for(j=0; j<w; j++)
		{
			tmp = *(src+j);
			//BGR convert to RGB
			color =  (tmp&0x001F)<<11;
			color += (tmp&0x07E0);
			color += (tmp&0xF800)>>11;

*(line_buf+j) = color;
		}

write(fd, line_buf, pitch);
#else
		write(fd, src, pitch);
#endif
	}
#ifdef BGR_CONVERT_TO_RGB
	rt_free(line_buf);
#endif
tick = rt_tick_get()-tick;
rt_kprintf("tick=%d
",tick);
	close(fd);
}
#ifdef RT_USING_FINSH
#include <finsh.h>
FINSH_FUNCTION_EXPORT(bmp_create, create a bitmap.);
#endif
```

需要将
```c
#ifndef BI_RGB
#define BI_RGB   0
#define BI_RLE8   1
#define BI_RLE4   2
#define BI_BITFIELDS   3
#endif
```

和结构体
```c
struct rtgui_image_bmp
struct rtgui_image_bmp_header
```
从`imag_bmp.c`移到`image_bmp.h`中，使用时在C文件中包含`image_bmp.h`文件。
在结构体`struct rtgui_image_bmp_header`之前加入
`#pragma pack(2)` 使结构体变量2字节对齐。