hud项目lcd调试

    #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;
        struct fb_cmap cmapinfo;
        long int screensize = 0;
        char *fbp = 0;
        int x = 0, y = 0;
        long int location = 0;
            int b,g,r;
        // Open the file for reading and writing
        fbfd = open("/dev/fb0", O_RDWR);                    // 打开Frame Buffer设备
        if (fbfd < 0) {
                    printf("Error: cannot open framebuffer device.%x
",fbfd);
                    exit(1);
        }
        printf("The framebuffer device was opened successfully.
");

        // Get fixed screen information
        if (ioctl(fbfd, FBIOGET_FSCREENINFO, &finfo)) {            // 获取设备固有信息
                    printf("Error reading fixed information.
");
                    exit(2);
        }
            printf(finfo.id);
        printf("
type:0x%x
", finfo.type );                            // FrameBuffer 类型,如0为象素
        printf("visual:%d
", finfo.visual );                        // 视觉类型：如真彩2，伪彩3
        printf("line_length:%d
", finfo.line_length );        // 每行字节长度
        printf("
smem_start:0x%x,smem_len:%d
", finfo.smem_start, finfo.smem_len ); // 显存起始地址和显存大小
        printf("mmio_start:0x%x ,mmio_len:%d
", finfo.mmio_start, finfo.mmio_len );
        
        // Get variable screen information
        if (ioctl(fbfd, FBIOGET_VSCREENINFO, &vinfo)) {            // 获取设备可变信息
                    printf("Error reading variable information.
");
                    exit(3);
        }
        printf("%dx%d, %dbpp
", vinfo.xres, vinfo.yres, vinfo.bits_per_pixel );
        // Figure out the size of the screen in bytes
        screensize = vinfo.xres * vinfo.yres * vinfo.bits_per_pixel / 8;　// 申请存放整个屏幕颜色数据的内存大小
        // Map the device to memory 通过mmap系统调用将framebuffer内存映射到用户空间,并返回映射后的起始地址
        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.
");
                    exit(4);
        }
        printf("The framebuffer device was mapped to memory successfully.
");
        
        vinfo.xoffset = (480-240)/2; // (计算屏幕图像在屏幕中间一块区域显示)Where we are going to put the pixel (x坐标偏移量：120) 要分清一块屏有宽和高，宽即用x坐标表示，高用y表示，和直角坐标系一样
        vinfo.yoffset = (280-140)/2; // (y坐标偏移量：70) 即该区域的左上角的像素点坐标为（x,y）=（120,70）,右下角的坐标为(x,y)= (120+240,70+140)
             b = 10; // 即blue : 0000 0010
             g = 100; // A little green 即green: 0000 0100
             r = 100; // A lot of red 即red : 0000 0100
        // Figure out where in memory to put the pixel
        for ( y = 0; y < 140; y++ )                // 行扫描
            for ( x = 0; x < 240; x++ ) {            // 列扫描
        
             location = (x+vinfo.xoffset) * (vinfo.bits_per_pixel/8) +    // 定位到具体哪一行的第几个像素
                 (y+vinfo.yoffset) * finfo.line_length; //定位到哪一行(即该行的第一个像素的地址) 这两句即是实现求某一个像素的地址的功能
        
             if ( vinfo.bits_per_pixel == 32 ) {        //        
                            *(fbp + location) = b; // Some blue
                            *(fbp + location + 1) = g;             // A little green
                            *(fbp + location + 2) = r;             // A lot of red
                            *(fbp + location + 3) = 0;     // No transparency
             } else {          //16bpp: r:g:b=5:6:5                                                //assume 16bpp
        
                            unsigned short int t = r<<11 | g << 5 | b;
                            *((unsigned short int*)(fbp + location)) = t;
             }
        
            }
        munmap(fbp, screensize);
        close(fbfd);
        return 0;
    }