linux double buffering

http://pandorawiki.org/Kernel_interface

double buffering

This can be achieved using FBIOPAN_DISPLAY ioctl system call. For this you need to mmap framebuffer of double size

buffer1 = mmap(0, 800*480*2 * 2, PROT_WRITE, MAP_SHARED, fbdev, 0);
buffer2 = (char *)mem + 800*480*2;

Then to display buffer2 you would call:

struct fb_var_screeninfo fbvar;
ioctl(fbdev, FBIOGET_VSCREENINFO, &fbvar);
fbvar.yoffset = 480;
ioctl(fbdev, FBIOPAN_DISPLAY, &fbvar);

going back to buffer1 would be repeating above with fbvar.yoffset = 0. Tripple or quad buffering can be implemented using the same technique.

vertical sync

Linux has standard FBIO_WAITFORVSYNC for this:

int arg = 0;
ioctl(fbdev, FBIO_WAITFORVSYNC, &arg);

be sure to pass argument value 0 or it will not work.

Some toolchains don't have FBIO_WAITFORVSYNC defined in <linux/fb.h>, in which case you can define it in the following manner:

#ifndef FBIO_WAITFORVSYNC
  #define FBIO_WAITFORVSYNC _IOW('F', 0x20, __u32)
#endif

经过测试发现，双缓冲绘图，切换频率超过显示器刷新频率60时，会出现闪烁，还未找到解决办法，也许就是不能超过刷新频率吧。