因為Linux是工作在保護模式下,所以用戶態進程是無法象DOS那樣使用顯卡BIOS里提供的中斷調用來實現直接寫屏,故Linux抽象出FrameBuffer這個設備來供用戶態進程實現直接寫屏。
在繼續下面的之前,先說明幾個背景知識:
好,現在可以讓我們開始實現直接寫屏:
好象很簡單哦~
fbtools.h
代碼:
#ifndef _FBTOOLS_H_
#define _FBTOOLS_H_
#include <linux/fb.h>
/a framebuffer device structure;
typedef struct fbdev{
int fb;
unsigned long fb_mem_offset;
unsigned long fb_mem;
struct fb_fix_screeninfo fb_fix;
struct fb_var_screeninfo fb_var;
char dev[20];
} FBDEV, *PFBDEV;
/open & init a frame buffer
/to use this function,
/you must set FBDEV.dev=\"/dev/fb0\"
/or \"/dev/fbX\"
/it\'s your frame buffer.
int fb_open(PFBDEV pFbdev);
/close a frame buffer
int fb_close(PFBDEV pFbdev);
/get display depth
int get_display_depth(PFBDEV pFbdev);
/full screen clear
void fb_memset(void *addr, int c, size_t len);
#endif
fbtools.c
代碼:
#include <stdio.h>
#include <stdlib.h>
#include <fcntl.h>
#include <unistd.h>
#include <string.h>
#include <sys/ioctl.h>
#include <sys/mman.h>
#include <asm/page.h>
#include \"fbtools.h\"
#define TRUE 1
#define FALSE 0
#define MAX(x,y) ((x)>(y)?(x):(y))
#define MIN(x,y) ((x)<(y)?(x):(y))
/open & init a frame buffer
int fb_open(PFBDEV pFbdev)
{
pFbdev->fb = open(pFbdev->dev, O_RDWR);
if(pFbdev->fb < 0)
{
printf(\"Error opening %s: %m. Check kernel config\\n\", pFbdev->dev);
return FALSE;
}
if (-1 == ioctl(pFbdev->fb,FBIOGET_VSCREENINFO,&(pFbdev->fb_var)))
{
printf(\"ioctl FBIOGET_VSCREENINFO\\n\");
return FALSE;
}
if (-1 == ioctl(pFbdev->fb,FBIOGET_FSCREENINFO,&(pFbdev->fb_fix)))
{
printf(\"ioctl FBIOGET_FSCREENINFO\\n\");
return FALSE;
}
/map physics address to virtual address
pFbdev->fb_mem_offset = (unsigned long)(pFbdev->fb_fix.smem_start) & (~PAGE_MASK);
pFbdev->fb_mem = (unsigned long int)mmap(NULL, pFbdev->fb_fix.smem_len +
pFbdev->fb_mem_offset,
PROT_READ | PROT_WRITE, MAP_SHARED, pFbdev->fb, 0);
if (-1L == (long) pFbdev->fb_mem)
{
printf(\"mmap error! mem:%d offset:%d\\n\", pFbdev->fb_mem,
pFbdev->fb_mem_offset);
return FALSE;
}
return TRUE;
}
/close frame buffer
int fb_close(PFBDEV pFbdev)
{
close(pFbdev->fb);
pFbdev->fb=-1;
}
/get display depth
int get_display_depth(PFBDEV pFbdev);
{
if(pFbdev->fb<=0)
{
printf(\"fb device not open, open it first\\n\");
return FALSE;
}
return pFbdev->fb_var.bits_per_pixel;
}
/full screen clear
void fb_memset (void *addr, int c, size_t len)
{
memset(addr, c, len);
}
/use by test
#define DEBUG
#ifdef DEBUG
main()
{
FBDEV fbdev;
memset(&fbdev, 0, sizeof(FBDEV));
strcpy(fbdev.dev, \"/dev/fb0\");
if(fb_open(&fbdev)==FALSE)
{
printf(\"open frame buffer error\\n\");
return;
}
fb_memset(fbdev.fb_mem + fbdev.fb_mem_offset, 0, fbdev.fb_fix.smem_len);
fb_close(&fbdev);
}
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