飞凌嵌入式ElfBoard ELF1板卡-LCD显示图片编程示例之编程步骤
打开bmp文件//打开.bmp文件
FILE *fb = fopen(bmpname, "rb");
if (fb == NULL)
{
printf("fopen bmp error\r\n");
return -1;
}
获取lcd参数
查看<linux/fb.h>
struct fb_var_screeninfo {
__u32 xres; /* visible resolution */
__u32 yres;
__u32 xres_virtual; /* virtual resolution */
__u32 yres_virtual;
__u32 xoffset; /* offset from virtual to visible */
__u32 yoffset; /* resolution */
__u32 bits_per_pixel; /* guess what */
__u32 grayscale; /* 0 = color, 1 = grayscale, */
/* >1 = FOURCC */
struct fb_bitfield red; /* bitfield in fb mem if true color, */
struct fb_bitfield green; /* else only length is significant */
struct fb_bitfield blue;
struct fb_bitfield transp; /* transparency */
__u32 nonstd; /* != 0 Non standard pixel format */
__u32 activate; /* see FB_ACTIVATE_* */
__u32 height; /* height of picture in mm */
__u32 width; /* width of picture in mm */
__u32 accel_flags; /* (OBSOLETE) see fb_info.flags */
/* Timing: All values in pixclocks, except pixclock (of course) */
__u32 pixclock; /* pixel clock in ps (pico seconds) */
__u32 left_margin; /* time from sync to picture */
__u32 right_margin; /* time from picture to sync */
__u32 upper_margin; /* time from sync to picture */
__u32 lower_margin;
__u32 hsync_len; /* length of horizontal sync */
__u32 vsync_len; /* length of vertical sync */
__u32 sync; /* see FB_SYNC_* */
__u32 vmode; /* see FB_VMODE_* */
__u32 rotate; /* angle we rotate counter clockwise */
__u32 colorspace; /* colorspace for FOURCC-based modes */
__u32 reserved; /* Reserved for future compatibility */
};
头文件中，用fb_var_screeninfo结构体定义屏幕参数基本信息，如分辨率，像素点位数及RGB分别用多少位表示。
获取结构体fb_var_screeninfo
//获取屏幕信息
//若屏幕显示区域大小不合适，可用ioctl(dev_fd, FBIOPUT_VSCREENINFO, &scrinfo)设置
if (ioctl(dev_fd, FBIOGET_VSCREENINFO, &scrinfo))
{
printf("get screen infomation error!\r\n");
return -1;
}
使用ioctl的参数，FBIOGET_VSCREENINFO来表示获得屏幕的可变信息。
映射framebuffer
//计算需要的映射内存大小
screensize = scrinfo.xres_virtual * scrinfo.yres_virtual * scrinfo.bits_per_pixel / 8;
// printf("screensize=%lu!\r\n", screensize);
//内存映射
fbp = (char *)mmap(NULL, screensize, PROT_READ | PROT_WRITE, MAP_SHARED, dev_fd, 0);
if (-1 == (int)fbp)
{
printf("mmap error!\r\n");
return -1;
}
首先计算需要的映射内存大小，计算公式为：映射内存大小 = 屏幕大小 = xres * yres * 每个像素位数 / 8。然后使用mmap映射内存，PROT_READ | PROT_WRITE表示该区域可读、可写；MAP_SHARED表示该区域是共享的，APP写入数据时，会直达驱动程序。到这一步之后就做好显示图片的准备了。
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