Linux framebuffer測試程序

　　Linux framebuffer的框架非常簡單， 對於應用程序就是操作一塊內存（俗稱幀緩存）， 當然也有可能是雙緩存， 一般用於高幀率場景， 一塊幀在填充數據時， 另一塊在顯示， 接着對調過來，

那通過設置哪里告知驅動層讀取哪塊幀數據呢？ 答案是用vinfo.xoffset， vinfo.yoffset

　　需要注意的是， 無論用write()、還是mmap()后直接操作內存都只是填充內存而已， 並不代表能夠立馬顯示， 這得看驅動， 如果驅動實現了自刷新（不斷從幀緩存拿數據刷到LCD上）， 那填充數據到幀緩存就會立馬顯示出來，

如果驅動沒有實現，那應用程序需要主動的調用 ioctl(fp, FBIOPAN_DISPLAY, &vinfo);， 告知驅動可以刷數據了， 如果這都沒顯示出來， 估計驅動沒實現FBIOPAN_DISPLAY功能。

示例代碼：（驅動實現自刷新， 應用依次顯示黃、藍、紅，最后畫線）

#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=0; i<psize; i++) {
        *fb_addr = bit_map;
        fb_addr++;
    }
}

int main ()   
{  
    int fp=0;  
    struct fb_var_screeninfo vinfo;  
    struct fb_fix_screeninfo finfo;  
    long screensize=0;  
    char *fbp = NULL, *test_fbp=NULL;    
    int x = 0, y = 0;  
    long location = 0;
    int i;
    int num = 5;
    int pix_size=0;

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

    if(fp < 0) {  
        printf("Error : Can not open framebuffer device/n");  
        exit(1);  
    }  

    if(ioctl(fp, FBIOGET_FSCREENINFO, &finfo)){  
        printf("Error reading fixed information/n");  
        exit(2);  
    }  

    if(ioctl(fp, FBIOGET_VSCREENINFO, &vinfo)){  
        printf("Error reading variable information/n");  
        exit(3);  
    }  

    screensize = vinfo.xres * vinfo.yres * vinfo.bits_per_pixel / 8;  

    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(0, screensize, PROT_READ | PROT_WRITE, MAP_SHARED, fp,0);  
    if ((int)fbp == -1)  
    {    
        printf ("Error: failed to map framebuffer device to memory./n");  
        exit (4);  
    }
    printf("Get virt mem = %p\n", fbp);  


    pix_size = vinfo.xres * vinfo.yres;
    /* using first frame, for FBIOPAN_DISPLAY
     * 當刷新需要調用FBIOPAN_DISPLAY， 要告知驅動刷哪塊幀， 用到下面兩個參數
     * 如果使用第二幀buffer -> vinfo.xoffset = 0; vinfo.yoffset = vinfo.yres;
     */
    vinfo.xoffset = 0;
    vinfo.yoffset = 0;

    /* show color loop */
    while(num--) {
        printf("\ndrawing YELLOW......\n");
        fill_color16((short *)fbp, YELLOW, pix_size);
        //ioctl(fp, FBIOPAN_DISPLAY, &vinfo);
        sleep(3);

        printf("\ndrawing BLUE......\n");
        fill_color16((short *)fbp, BLUE, pix_size);
        //ioctl(fp, FBIOPAN_DISPLAY, &vinfo);
        sleep(3);
        
        printf("\ndrawing RED......\n");
        fill_color16((short *)fbp, RED, pix_size);
        //ioctl(fp, FBIOPAN_DISPLAY, &vinfo);
        sleep(3);
    }
#if 1
    /*這是你想畫的點的位置坐標,(0，0)點在屏幕左上角*/    
    x = 10;  
    y = 10;  
    location = x * (vinfo.bits_per_pixel / 8) + y  *  finfo.line_length;  
    test_fbp = fbp + location;
    printf("draw line.......\n");
    for(i = 0; i < (vinfo.xres - x); i++)
        *test_fbp++ = i+30;

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

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

    close (fp);
    return 0;
}  

 

當然用read()/write()， 也可以， 就是效率非常低， 太多系統調用導致系統在用戶態和kernel態切換， 而且每次還傳輸一個字節， 但作為例子可以參考一下：

#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=0;  
    struct fb_var_screeninfo vinfo;  
    int i;
    int pix_size=0;
    unsigned char color1, color2;

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

    if(fp < 0) {  
        printf("Error : Can not open framebuffer device/n");  
        exit(1);  
    }  

    if(ioctl(fp, FBIOGET_VSCREENINFO, &vinfo)){  
        printf("Error reading variable information/n");  
        exit(3);  
    }  


    pix_size = vinfo.xres * vinfo.yres;
    color1 = 0;
    color2 = 0xf8;
    for(i=0; i<pix_size; i++) {
        write(fp, &color1, 1);
        write(fp, &color2, 1);        
    }

    close (fp);
    return 0;
}