写入帧缓冲区

Question

写入帧缓冲区

9

我正在使用一个内置图形加速器GMA-HD的i5核心，运行在RHEL 6.0操作系统上。我需要测试显卡驱动程序的图形加速能力（我发现我的PC上的驱动程序是i915）。我使用了以下代码（从互联网上获得并进行了一些修改）来写入framebuffer。

#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;
}

在运行上述代码后，屏幕上没有任何变化，但“ cat /dev/fb0”显示了一些数据。有人能解释一下为什么屏幕上没有看到任何东西吗？（我还发现fb0对应于帧缓冲“inteldrmfb”。）

提前致谢，

尼拉吉N.T

- NRJ

你看到屏幕闪了一下吗？（盲目尝试） - drahnr

我猜你刚刚写了一个红色强度为255/65535的像素。那么Vinfo.bpp printf的输出是什么？ - ninjalj

1个回答

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- shodanex · Accepted Answer

你没有增加位置！所以255只在第一个像素上，而其他所有像素都为0。请尝试以下代码：

        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;   
        }

然而，对于测试来说，使用directfb可能是正确的选择。它带有一些帧缓存性能测试。