c++ - 在 Linux (Debian) 中访问文本屏幕内存

Question

我正在寻找如何读取文本屏幕上的屏幕内存。基本上我正在编写一个Linux应用程序，它使用扩展字符集(unicode)在屏幕上绘制一个“窗口”。我需要准备好要重写的屏幕区域，以便在“窗口”关闭时可以替换该区域。

谢谢

Answer 1

在控制台中，您可以保存 frame buffer 的内容.

通常可以通过 /dev/fb0 访问，它没有加速，但可靠。

这是一个功能明确的小示例。

#include <stdlib.h>
#include <unistd.h>
#include <stdio.h>
#include <fcntl.h>
#include <string.h>

#include <sys/mman.h>
#include <sys/ioctl.h>

#include <linux/fb.h>

#define red pixel {0xFF,0,0,0}

typedef struct s_Pixel {
    char r;
    char g;
    char b;
    char a;
}pixel;

typedef struct s_Framebuffer {
    void*   ptr;
    int     hauteur;
    int     largeur;
    int linelength;
}Framebuffer;

void FB_close   ();
void FB_init    (Framebuffer *);
void FB_clear   (int);
void FB_setPixel(int,int,char,char,char,char);

char        *fbp;
int         fbfd;
long int    screensize;

struct  fb_var_screeninfo vinfo;
struct  fb_fix_screeninfo finfo;

void FB_setPixel(int x, int y, char r, char g, char b, char a)
{
    char * p = (char*)fbp + (x * 4) + (y * finfo.line_length); 
    p[0] = r;
    p[1] = g;
    p[2] = b;
    p[3] = a;
}

void FB_close()
{
    munmap(fbp, screensize);
    close(fbfd);
}

void FB_init(Framebuffer* fb)
{

    // Open the file for reading and writing
    fbfd = open("/dev/fb0", O_RDWR);

    if (fbfd == -1) {
        perror("Error: cannot open framebuffer device");
        exit(1);
    }

    // Get fixed screen information
    if (ioctl(fbfd, FBIOGET_FSCREENINFO, &finfo) == -1) {
        perror("Error reading fixed information");
        exit(2);
    }

    // Get variable screen information
    if (ioctl(fbfd, FBIOGET_VSCREENINFO, &vinfo) == -1) {
        perror("Error reading variable information");
        exit(3);
    }

    // Figure out the size of the screen in bytes
    screensize = vinfo.xres * vinfo.yres * vinfo.bits_per_pixel / 8;

    // Map the device to memory
    fbp = (char *)mmap(0, screensize, PROT_READ | PROT_WRITE, MAP_SHARED, fbfd, 0);
    if ((int)fbp == -1) {
        perror("Error: failed to map framebuffer device to memory");
        exit(4);
    }

    fb->ptr = fbp;
    fb->largeur = vinfo.xres;
    fb->hauteur = vinfo.yres;
    fb->linelength = finfo.line_length;

    FB_clear    ( 0x0 );

    //trace(T1,"%dx%d, %dbpp\n", vinfo.xres, vinfo.yres, vinfo.bits_per_pixel);
}

void FB_clear(int color)
{
    unsigned int x,y;
    switch (vinfo.bits_per_pixel)
    {
        case 32:
            memset((int*)fbp,color,screensize);
            break;
        default:
            for (y=0;y<vinfo.yres;y++)
            {
                for (x=0;x<vinfo.xres;x++)
                {
                    fbp[x * 4 + y *finfo.line_length] = 0x0;
                    fbp[1 + x * 4 + y * finfo.line_length] = 0x0;
                    fbp[2 + x * 4 + y * finfo.line_length] = 0x0;
                }
            }
            break;
    }

}

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