飛凌嵌入式ElfBoard ELF 1板卡-LCD顯示圖片編程示例之編程步驟

打開(kāi)bmp文件

//打開(kāi).bmp文件

    FILE *fb = fopen(bmpname, "rb");

    if (fb == NULL)

    {

        printf("fopen bmp errorrn");

        return -1;

    }

獲取lcd參數(shù)

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 */

};

頭文件中，用fb_var_screeninfo結(jié)構(gòu)體定義屏幕參數(shù)基本信息，如分辨率，像素點(diǎn)位數(shù)及RGB分別用多少位表示。

獲取結(jié)構(gòu)體fb_var_screeninfo

//獲取屏幕信息

    //若屏幕顯示區(qū)域大小不合適，可用ioctl(dev_fd, FBIOPUT_VSCREENINFO, &scrinfo)設(shè)置

    if (ioctl(dev_fd, FBIOGET_VSCREENINFO, &scrinfo))

    {

        printf("get screen infomation error!rn");

        return -1;

    }

使用ioctl的參數(shù)，F(xiàn)BIOGET_VSCREENINFO來(lái)表示獲得屏幕的可變信息。

映射framebuffer

//計(jì)算需要的映射內(nèi)存大小

    screensize = scrinfo.xres_virtual * scrinfo.yres_virtual * scrinfo.bits_per_pixel / 8;

    // printf("screensize=%lu!rn", screensize);




    //內(nèi)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;

    }

首先計(jì)算需要的映射內(nèi)存大小，計(jì)算公式為：映射內(nèi)存大小 = 屏幕大小 = xres * yres * 每個(gè)像素位數(shù) / 8。然后使用mmap映射內(nèi)存，PROT_READ | PROT_WRITE表示該區(qū)域可讀、可寫(xiě)；MAP_SHARED表示該區(qū)域是共享的，APP寫(xiě)入數(shù)據(jù)時(shí)，會(huì)直達(dá)驅(qū)動(dòng)程序。到這一步之后就做好顯示圖片的準(zhǔn)備了。