Linux FrameBuffer（三）- struct fb_fix_screeninfo 和 struct fb_var_screeninfo 详解

目录
一、概述
二、struct fb_fix_screeninfo详解
 2.1 struct fb_fix_screeninfo定义
 2.2 struct fb_fix_screeninfo字段说明：
三、struct fb_var_screeninfo详解
 3.1 struct fb_var_screeninfo定义：
 3.2 struct fb_var_screeninfo字段说明：
四、打印 struct fb_fix_screeninfo 和 struct fb_var_screeninfo

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一、概述

struct fb_fix_screeninfo 和 struct fb_var_screeninfo 都定义在系统的/usr/include/linux/fb.h文件内。下面分别结构体定义、结构体字段说明两部分来详细解释这两个结构体。

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二、struct fb_fix_screeninfo详解

struct fb_fix_screeninfo主要用于获取FrameBuffer的固定信息，这些信息无法在应用层被更改，只能通过ioctl函数使用FBIOGET_FSCREENINFO去获取。

2.1 struct fb_fix_screeninfo定义：

struct fb_fix_screeninfo {
	char id[16];			/* identification string eg "TT Builtin" */
	unsigned long smem_start;	/* Start of frame buffer mem (physical address) */
	__u32 smem_len;			/* Length of frame buffer mem	*/
	__u32 type;				/* see FB_TYPE_*				*/
	__u32 type_aux;			/* Interleave for interleaved Planes */
	__u32 visual;			/* see FB_VISUAL_*				*/ 
	__u16 xpanstep;			/* zero if no hardware panning  */
	__u16 ypanstep;			/* zero if no hardware panning  */
	__u16 ywrapstep;		/* zero if no hardware ywrap    */
	__u32 line_length;		/* length of a line in bytes    */
	unsigned long mmio_start;/* Start of Memory Mapped I/O (physical address) */
	__u32 mmio_len;			/* Length of Memory Mapped I/O  */
	__u32 accel;			/* Indicate to driver which*//*specific chip/card we have	*/
	__u16 capabilities;		/* see FB_CAP_*					*/
	__u16 reserved[2];		/* Reserved for future compatibility */
};
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2.2 struct fb_fix_screeninfo字段说明：

表格中提到的宏如FB_TYPE_PACKED_PIXELS、FB_VISUAL_TRUECOLOR、FB_ACCEL_NONE请查看 /usr/include/linux/fb.h 的相关定义。

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三、struct fb_var_screeninfo详解

struct fb_var_screeninfo主要用于获取和设置FrameBuffer的可变屏幕信息，包括分辨率、像素位深、像素格式等。这些信息可以通过ioctl函数使用FBIOGET_VSCREENINFO获取，也可以通过FBIOPUT_VSCREENINFO修改。

3.1 struct fb_var_screeninfo定义：

struct fb_var_screeninfo {
	__u32 xres;				/* visible resolution		*/
	__u32 yres;
	__u32 xres_virtual;		/* virtual resolution		*/
	__u32 yres_virtual;
	__u32 xoffset;			/* offset from virtual to visible */
	__u32 yoffset;			/* resolution			*/

	__u32 bits_per_pixel;	/* guess what			*/
	__u32 grayscale;		/* 0 = color, 1 = grayscale,*//* >1 = FOURCC*/
	
	struct fb_bitfield red;		/* bitfield in fb mem if true color, */
	struct fb_bitfield green;	/* else only length is significant */
	struct fb_bitfield blue;
	struct fb_bitfield transp;	/* transparency			*/	

	__u32 nonstd;			/* != 0 Non standard pixel format 	*/
	__u32 activate;			/* see FB_ACTIVATE_*				*/
	__u32 height;			/* height of picture in mm  		*/
	__u32 width;			/* width of picture in mm   		*/
	__u32 accel_flags;		/* (OBSOLETE) see fb_info.flags 	*/

	/* Timing: All values in pixclocks, except pixclock (of course) */
	__u32 pixclock;			/* pixel clock in ps (pico seconds) */
	__u32 left_margin;		/* time from sync to picture	*/
	__u32 right_margin;		/* time from picture to sync	*/
	__u32 upper_margin;		/* time from sync to picture	*/
	__u32 lower_margin;
	__u32 hsync_len;		/* length of horizontal sync*/
	__u32 vsync_len;		/* length of vertical sync	*/
	__u32 sync;				/* see FB_SYNC_*		*/
	__u32 vmode;			/* see FB_VMODE_*		*/
	__u32 rotate;			/* angle we rotate counter clockwise */
	__u32 reserved[5];		/* Reserved for future compatibility */
};
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3.2 struct fb_var_screeninfo字段说明：

表格中提到的宏和结构体请查看 /usr/include/linux/fb.h 的相关定义。

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四、打印 struct fb_fix_screeninfo 和 struct fb_var_screeninfo

复制下面代码保存为printFbInfo.c，编译后，在ubuntu系统上，加上sudo执行，就可以看到FrameBuffer的固定信息和可变信息了，再结合上面的说明，可以更好地理解这两个结构体。

#include 
#include 

#include 
#include 
#include 

void print_finfo(struct fb_fix_screeninfo *finfo)
{
    fprintf(stderr,"Printing fb_fix_screeninfo:\n");
    fprintf(stderr,"smem_start=%p,smem_len=%d\n",(char *)finfo->smem_start,finfo->smem_len);
    fprintf(stderr,"type = %d\n", finfo->type);
    fprintf(stderr,"type_aux = %d\n", finfo->type_aux);
    fprintf(stderr,"visual = %d\n", finfo->visual);
    fprintf(stderr,"xpanstep = %d, ypanstep = %d\n", finfo->xpanstep,finfo->ypanstep);
    fprintf(stderr,"ywrapstep = %d\n", finfo->ywrapstep);
    fprintf(stderr,"line_length = %d\n", finfo->line_length);
    fprintf(stderr,"mmio_start=%p, mmio_len=%d\n",(char *)finfo->mmio_start,finfo->mmio_len);
    fprintf(stderr,"accel = %d\n\n", finfo->accel);
}
void print_vinfo(struct fb_var_screeninfo *vinfo)
{
    fprintf(stderr, "Printing vinfo:\n");
    fprintf(stderr, "xres:%d, yres:%d\n", vinfo->xres,vinfo->yres);
    fprintf(stderr, "xres_virtual:%d, yres_virtual:%d\n", vinfo->xres_virtual,vinfo->yres_virtual);
    fprintf(stderr, "xoffset:%d, yoffset:%d\n", vinfo->xoffset,vinfo->yoffset);
    fprintf(stderr, "bits_per_pixel: %d\n", vinfo->bits_per_pixel);
    fprintf(stderr, "grayscale: %d\n", vinfo->grayscale);
	fprintf(stderr, "red: %d/%d\n", vinfo->red.length, vinfo->red.offset);
    fprintf(stderr, "green: %d/%d\n", vinfo->green.length, vinfo->green.offset);
    fprintf(stderr, "blue: %d/%d\n", vinfo->blue.length, vinfo->blue.offset);
    fprintf(stderr, "transp: %d/%d\n", vinfo->transp.length, vinfo->transp.offset);
    fprintf(stderr, "nonstd: %d\n", vinfo->nonstd);
    fprintf(stderr, "activate: %d\n", vinfo->activate);
    fprintf(stderr, "height: %d\n", vinfo->height);
    fprintf(stderr, "width: %d\n", vinfo->width);
    fprintf(stderr, "accel_flags: %d\n", vinfo->accel_flags);
    fprintf(stderr, "pixclock: %d\n", vinfo->pixclock);
    fprintf(stderr, "left_margin: %d\n", vinfo->left_margin);
    fprintf(stderr, "right_margin: %d\n", vinfo->right_margin);
    fprintf(stderr, "upper_margin: %d\n", vinfo->upper_margin);
    fprintf(stderr, "lower_margin: %d\n", vinfo->lower_margin);
    fprintf(stderr, "hsync_len: %d\n", vinfo->hsync_len);
    fprintf(stderr, "vsync_len: %d\n", vinfo->vsync_len);
    fprintf(stderr, "sync: %d\n", vinfo->sync);
    fprintf(stderr, "vmode: %d\n", vinfo->vmode);
	fprintf(stderr, "rotate: %d\n\n", vinfo->rotate);
}

int main(int argc, char *argv[])
{
	// 1.打开设备
	char fbPath[64] = "/dev/fb0";
	int framebuf_fd = open(fbPath, O_RDWR);
	if ( framebuf_fd < 0 ) {
        printf("[%s:%d] open %s error \n", __FILE__,__LINE__,fbPath);
        return -1;
    }
	
	// 2.获取设备固定参数
	struct fb_fix_screeninfo finfo;
	if (ioctl(framebuf_fd, FBIOGET_FSCREENINFO, &finfo) < 0)
    {
        fprintf(stderr, "ioctl FBIOGET_FSCREENINFO err \r\n");
        return -1;
    }
	print_finfo(&finfo);

	// 3.1 获取虚拟参数
	struct fb_var_screeninfo vinfo;
    if (ioctl(framebuf_fd, FBIOGET_VSCREENINFO, &vinfo) < 0)
    {
        fprintf(stderr, "ioctl FBIOGET_VSCREENINFO err \r\n");
        return -1;
    }
	print_vinfo(&vinfo);
	
	return 0;
}
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