Linux 写入帧缓冲区
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Writing to frame buffer
提问by NRJ
I'm using an i5 core with builtin graphics accelerator GMA-HD running on an RHEL 6.0 OS. I needed to test the graphics acceleration capabilities of the graphics driver(which I found out was i915 in my PC). I used the following code(which I got from the internet with some modifications) for writing to framebuffer.
我使用的是在 RHEL 6.0 操作系统上运行的带有内置图形加速器 GMA-HD 的 i5 内核。我需要测试图形驱动程序的图形加速功能（我发现我的电脑是 i915）。我使用以下代码（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;
}
After running the above code no change was found on display but ' cat /dev/fb0 ' showed some data. Could someone explain why nothing was seen on screen? (I also found that fb0 correspond to the frame buffer 'inteldrmfb' .)
运行上述代码后，显示器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' 。）
Thanks in advance,
提前致谢，
Neeraj N.T
尼拉吉NT
回答by shodanex
You are not increasing location ! So 255 is only on the first pixel, and all the others are 0. Try this instead :
你不是在增加位置！所以 255 只在第一个像素上，其他的都是 0。试试这个：
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;
}
However, may be the right thing to do for testing is to use directfbIt comes with some framebuffer performance test
但是，测试可能正确的做法是使用directfb自带的一些帧缓冲性能测试
