c – 写入帧缓冲区

我正在使用运行在RHEL 6.0操作系统上的内置图形加速器GMA-HD的i5内核.
我需要测试图形驱动程序的图形加速功能(我发现在我的电脑中是i915).
我使用下面的代码(我从互联网上得到了一些修改)来写入帧缓冲区.

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

int main()
{
        int fbfd = 0;
        struct fb_var_screeninfo vinfo;
        struct fb_fix_screeninfo finfo;
        long int screensize = 0;
         char *fbp = 0;
        int x = 0, y = 0;
        long int location = 0;
        int count ;

        /* Open the file for reading and writing */
        fbfd = open("/dev/fb0", O_RDWR);
        if (!fbfd) {
                printf("Error: cannot open framebuffer device.\n");
                exit(1);
        }
        printf("The framebuffer device was opened successfully.\n");
     /* Get fixed screen information */
        if (ioctl(fbfd, FBIOGET_FSCREENINFO, &finfo)) {
               printf("Error reading fixed information.\n");
                exit(2);
        }

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

        /* Figure out the size of the screen in bytes */
        screensize = vinfo.xres * vinfo.yres * vinfo.bits_per_pixel / 8;
        printf("\nScreen size is %d",screensize);
        printf("\nVinfo.bpp = %d",vinfo.bits_per_pixel);

        /* Map the 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 to memory.\n");
                exit(4);
        }
         printf("The framebuffer device was mapped to memory successfully.\n");


        x = 100; y = 100; /* Where we are going to put the pixel */

        /* Figure out where in memory to put the pixel */
        location = (x+vinfo.xoffset) * (vinfo.bits_per_pixel/8) + (y+vinfo.yoffset) * finfo.line_length;
        for(count = 1 ;count < 100 ;count++)
        {
                *(fbp + location) = 255;    /* Some blue */
                *(fbp + location + count) = 0; /* A little green */
                *(fbp + location + count + 1) = 0; /* A lot of red */
                *(fbp + location + count + 2) = 0; /* No transparency */
        }
        munmap(fbp, screensize);
        close(fbfd);
        return 0;
}

运行上面的代码后,显示没有变化,但’cat / dev / fb0’显示了一些数据.
有人可以解释为什么屏幕上看不到任何内容？
(我还发现fb0对应于帧缓冲区’inteldrmfb’.)

提前致谢,

Neeraj N.T

解决方法:

你没有增加位置！因此255仅在第一个像素上,而所有其他像素都是0.请尝试相反：

        location = (x+vinfo.xoffset) * (vinfo.bits_per_pixel/8) + (y+vinfo.yoffset) * finfo.line_length;
        for(count = 1 ;count < 100 ;count++)
        {
                *(fbp + location) = 255;    /* Some blue */
                *(fbp + location + 1) = 0; /* A little green */
                *(fbp + location + 2) = 0; /* A lot of red */
                *(fbp + location + 3) = 0; /* No transparency */
                location += 4;   
        }

但是,对于测试来说可能是正确的做法是使用directfb它来了
用一些帧缓冲性能测试

标签：c-3,framebuffer,linux
来源： https://codeday.me/bug/20190928/1827522.html