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Android操作framebuffer

分类： Framebuffer Camera Video 2011-06-09 17:43 248人阅读 评论(0) 收藏 举报

操作framebuffer的主要步骤如下：

1、打开一个可用的FrameBuffer设备；
2、通过mmap调用把显卡的物理内存空间映射到用户空间；
3、更改内存空间里的像素数据并显示；

4、退出时关闭framebuffer设备。

 

下面的这个例子简单地用framebuffer画了一个渐变的进度条，代码 framebuf.c 如下：

#include <unistd.h>
#include <stdio.h>
#include <fcntl.h>
#include <linux/fb.h>
#include <sys/mman.h>

inline static unsigned short int make16color(unsigned char r,unsigned char g, unsigned char b)
{
    return(
 (((r >> 3)& 31) << 11) |
 (((g >> 2)& 63) <<5)  |
  ((b >> 3)&31)       );
}

int main() {
    int fbfd =0;
    structfb_var_screeninfo vinfo;
    structfb_fix_screeninfo finfo;
    long intscreensize = 0;
 char *fbp = 0;
    int x = 0, y= 0;
    intguage_height = 20, step = 10;
    long intlocation = 0;

    // Openthe file for reading and writing
    fbfd =open("/dev/graphics/fb0", O_RDWR);
    if (!fbfd){
       printf("Error: cannot open framebuffer device./n");
       exit(1);
    }
    printf("Theframebuffer device was opened successfully./n");

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

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

 printf("sizeof(unsigned short) = %d/n",sizeof(unsigned short));
   printf("%dx%d, %dbpp/n", vinfo.xres, vinfo.yres,vinfo.bits_per_pixel );
 printf("xoffset:%d, yoffset:%d, line_length:%d/n", vinfo.xoffset, vinfo.yoffset, finfo.line_length );

    // Figureout the size of the screen in bytes
    screensize =vinfo.xres * vinfo.yres * vinfo.bits_per_pixel / 8;;

    // Mapthe device to memory
    fbp = (char*)mmap(0, screensize, PROT_READ | PROT_WRITE, MAP_SHARED,
                      fbfd, 0);

    if((int)fbp == -1) {
       printf("Error: failed to map framebuffer device tomemory./n");
       exit(4);
    }
    printf("Theframebuffer device was mapped to memory successfully./n");

 //set to black color first
 memset(fbp, 0, screensize);
    //drawrectangle
    y =(vinfo.yres - guage_height) / 2 -2;      // Where we are going to put the pixel
    for (x =step - 2; x < vinfo.xres - step + 2; x++) {
       location = (x+vinfo.xoffset) * (vinfo.bits_per_pixel/8) +
                      (y+vinfo.yoffset) * finfo.line_length;

       *((unsigned short int*)(fbp + location)) = 255;
    }

    y =(vinfo.yres + guage_height) / 2 +2;      // Where we are going to put the pixel
    for (x =step - 2; x < vinfo.xres - step + 2; x++) {
       location = (x+vinfo.xoffset) * (vinfo.bits_per_pixel/8) +
                      (y+vinfo.yoffset) * finfo.line_length;

       *((unsigned short int*)(fbp + location)) = 255;
    }

    x = step- 2;
    for (y =(vinfo.yres - guage_height) / 2 - 2; y < (vinfo.yres+ guage_height) / 2 + 2; y++) {
       location = (x+vinfo.xoffset) * (vinfo.bits_per_pixel/8) +
                      (y+vinfo.yoffset) * finfo.line_length;

       *((unsigned short int*)(fbp + location)) = 255;
    }

    x =vinfo.xres - step + 2;
    for (y =(vinfo.yres - guage_height) / 2 - 2; y < (vinfo.yres+ guage_height) / 2 + 2; y++) {
       location = (x+vinfo.xoffset) * (vinfo.bits_per_pixel/8) +
                      (y+vinfo.yoffset) * finfo.line_length;

       *((unsigned short int*)(fbp + location)) = 255;
    }

    // Figureout where in memory to put the pixel
    for ( x =step; x < vinfo.xres - step; x++ ) {
       for ( y = (vinfo.yres - guage_height) / 2; y <(vinfo.yres + guage_height) / 2; y++ ) {
           location = (x+vinfo.xoffset) * (vinfo.bits_per_pixel/8) +
                      (y+vinfo.yoffset) * finfo.line_length;

           if ( vinfo.bits_per_pixel == 32 ) {
               *(fbp + location) =100;       // Some blue
               *(fbp + location + 1) =15+(x-100)/2;    // A little green
               *(fbp + location + 2) =200-(y-100)/5;   // A lot of red
               *(fbp + location + 3) =0;     // No transparency
           } else { //assume 16bpp
               unsigned char b = 255 * x / (vinfo.xres - step);
               unsigned char g =255;    // (x - 100)/6 A little green
               unsigned char r =255;    // A lotof red
               unsigned short int t = make16color(r, g, b);
               *((unsigned short int*)(fbp + location)) = t;
           }
       }
  //printf("x = %d, temp = %d/n",x, temp);
       //sleep to see it
       usleep(200);
    }
    //cleanframebuffer
    munmap(fbp,screensize);
   close(fbfd);

    return0;
}

注意，在Android环境，framebuffer设备不是象linux一样的 /dev/fb0，而是 /dev/graphics/fb0 ，

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

打开framebuffer设备，

    fbp =(char *)mmap(0, screensize, PROT_READ | PROT_WRITE,MAP_SHARED,
                      fbfd, 0);

 

将设备map到一块内存，然后就可以操作这块内存空间来显示你想画的图形了。

最后别忘了关闭设备：

   munmap(fbp, screensize);
   close(fbfd);