飞凌嵌入式ElfBoard ELF 1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 errorrn");

        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[4];              /* 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!rn");

        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!rn", 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!rn");

        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。