写入帧缓冲区

Question

我使用的是带有内置图形加速器 GMA-HD 的 i5 内核，在 RHEL 6.0 操作系统上运行。 我需要测试显卡驱动程序的图形加速能力（我发现我的电脑上是i915）。 我使用以下代码（我从互联网上获得并进行了一些修改）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;
}

运行上述代码后，显示上没有发现任何变化，但“cat /dev/fb0”显示了一些数据。 有人可以解释为什么屏幕上什么也没有看到吗？ （我还发现 fb0 对应于帧缓冲区“inteldrmfb”。）

提前致谢，

Neeraj NT

Answer 1

你没有增加位置！因此 255 仅在第一个像素上，所有其他像素均为 0。请尝试这样做：

        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，测试时正确的做法可能是使用 directfb 它来了
一些帧缓冲区性能测试