Linux framebuffer测试程序

　　Linux framebuffer的框架非常简单，对于应用程序就是操作一块内存（俗称帧缓存），当然也有可能是双缓存，一般用于高帧率场景，一块帧在填充数据时，另一块在显示，接着对调过来，

那通过设置哪里告知驱动层读取哪块帧数据呢？答案是用vinfo.xoffset， vinfo.yoffset

　　需要注意的是，无论用write()、还是mmap()后直接操作内存都只是填充内存而已，并不代表能够立马显示，这得看驱动，如果驱动实现了自刷新（不断从帧缓存拿数据刷到LCD上），那填充数据到帧缓存就会立马显示出来，

如果驱动没有实现，那应用程序需要主动的调用 ioctl(fp, FBIOPAN_DISPLAY, &vinfo);，告知驱动可以刷数据了，如果这都没显示出来，估计驱动没实现FBIOPAN_DISPLAY功能。

示例代码：（驱动实现自刷新，应用依次显示黄、蓝、红，最后画线）

#include <unistd.h>

#include <stdio.h>

#include <fcntl.h>

#include <linux/fb.h>

#include <sys/mman.h>

#include <stdlib.h>

#include <string.h>

#define RED    0xF800

#define YELLOW    0xFFE0

#define BLUE     0x001F

#define WHITE    0xFFFF

#define BLACK    0x0000

void fill_color16(short *fb_addr, short bit_map, int psize)

{

    int i;

    for(i=; i<psize; i++) {

        *fb_addr = bit_map;

        fb_addr++;

    }

}

int main ()

{

    int fp=;

    struct fb_var_screeninfo vinfo;

    struct fb_fix_screeninfo finfo;

    long screensize=;

    char *fbp = NULL, *test_fbp=NULL;

    int x = , y = ;

    long location = ;

    int i;

    int num = ;

    int pix_size=;

    fp = open("/dev/graphics/fb0", O_RDWR);  

    if(fp < ) {

        printf("Error : Can not open framebuffer device/n");

        exit();

    }  

    if(ioctl(fp, FBIOGET_FSCREENINFO, &finfo)){

        printf("Error reading fixed information/n");

        exit();

    }  

    if(ioctl(fp, FBIOGET_VSCREENINFO, &vinfo)){

        printf("Error reading variable information/n");

        exit();

    }  

    screensize = vinfo.xres * vinfo.yres * vinfo.bits_per_pixel / ;  

    printf("The phy mem = 0x%x, total size = %d(byte)\n", finfo.smem_start, finfo.smem_len);

    printf("xres =  %d, yres =  %d, bits_per_pixel = %d\n", vinfo.xres, vinfo.yres, vinfo.bits_per_pixel);

    printf("So the screensize = %d(byte), using %d frame\n", screensize, finfo.smem_len/screensize);

    printf("vinfo.xoffset = %d, vinfo.yoffset = %d\n", vinfo.xoffset, vinfo.yoffset);

    printf("vinfo.vmode is :%d\n", vinfo.vmode);

    printf("finfo.ypanstep is :%d\n", finfo.ypanstep);

    printf("vinfo.red.offset=0x%x\n", vinfo.red.offset);

    printf("vinfo.red.length=0x%x\n", vinfo.red.length);

    printf("vinfo.green.offset=0x%x\n", vinfo.green.offset);

    printf("vinfo.green.length=0x%x\n", vinfo.green.length);

    printf("vinfo.blue.offset=0x%x\n", vinfo.blue.offset);

    printf("vinfo.blue.length=0x%x\n", vinfo.blue.length);

    printf("vinfo.transp.offset=0x%x\n", vinfo.transp.offset);

    printf("vinfo.transp.length=0x%x\n", vinfo.transp.length);

    fbp =(char *)mmap(, screensize, PROT_READ | PROT_WRITE, MAP_SHARED, fp,);

    if ((int)fbp == -)

    {

        printf ("Error: failed to map framebuffer device to memory./n");

        exit ();

    }

    printf("Get virt mem = %p\n", fbp);  

    pix_size = vinfo.xres * vinfo.yres;

    /* using first frame, for FBIOPAN_DISPLAY

     * 当刷新需要调用FBIOPAN_DISPLAY， 要告知驱动刷哪块帧， 用到下面两个参数

     * 如果使用第二帧buffer -> vinfo.xoffset = 0; vinfo.yoffset = vinfo.yres;

     */

    vinfo.xoffset = ;

    vinfo.yoffset = ;

    /* show color loop */

    while(num--) {

        printf("\ndrawing YELLOW......\n");

        fill_color16((short *)fbp, YELLOW, pix_size);

        //ioctl(fp, FBIOPAN_DISPLAY, &vinfo);

        sleep();

        printf("\ndrawing BLUE......\n");

        fill_color16((short *)fbp, BLUE, pix_size);

        //ioctl(fp, FBIOPAN_DISPLAY, &vinfo);

        sleep();

        printf("\ndrawing RED......\n");

        fill_color16((short *)fbp, RED, pix_size);

        //ioctl(fp, FBIOPAN_DISPLAY, &vinfo);

        sleep();

    }

#if 1

    /*这是你想画的点的位置坐标,(0，0)点在屏幕左上角*/

    x = ;

    y = ;

    location = x * (vinfo.bits_per_pixel / ) + y  *  finfo.line_length;

    test_fbp = fbp + location;

    printf("draw line.......\n");

    for(i = ; i < (vinfo.xres - x); i++)

        *test_fbp++ = i+;

    //ioctl(fp, FBIOPAN_DISPLAY, &vinfo);

#endif

    munmap(fbp, screensize); /*解除映射*/  

    close (fp);

    return ;

}

当然用read()/write()，也可以，就是效率非常低，太多系统调用导致系统在用户态和kernel态切换，而且每次还传输一个字节，但作为例子可以参考一下：

#include <unistd.h>

#include <stdio.h>

#include <fcntl.h>

#include <linux/fb.h>

#include <sys/mman.h>

#include <stdlib.h>

#include <string.h>

#define RED    0xF800

#define YELLOW    0xFFE0

#define BLUE     0x001F

#define WHITE    0xFFFF

#define BLACK    0x0000

int main ()

{

    int fp=;

    struct fb_var_screeninfo vinfo;

    int i;

    int pix_size=;

    unsigned char color1, color2;

    fp = open("/dev/graphics/fb0", O_RDWR);  

    if(fp < ) {

        printf("Error : Can not open framebuffer device/n");

        exit();

    }  

    if(ioctl(fp, FBIOGET_VSCREENINFO, &vinfo)){

        printf("Error reading variable information/n");

        exit();

    }  

    pix_size = vinfo.xres * vinfo.yres;

    color1 = ;

    color2 = 0xf8;

    for(i=; i<pix_size; i++) {

        write(fp, &color1, );

        write(fp, &color2, );

    }

    close (fp);

    return ;

}