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 ;
}