Android系统的开机画面显示过程分析（4）

        函数fb_show_logo_line也是实现在文件kernel/goldfish/drivers/video/fbmem.c中，如下所示：

static int fb_show_logo_line(struct fb_info *info, int rotate,
                             const struct linux_logo *logo, int y,
                             unsigned int n)
{
        u32 *palette = NULL, *saved_pseudo_palette = NULL;
        unsigned char *logo_new = NULL, *logo_rotate = NULL;
        struct fb_p_w_picpath p_w_picpath;

        /* Return if the frame buffer is not mapped or suspended */
        if (logo == NULL || info->state != FBINFO_STATE_RUNNING ||
            info->flags & FBINFO_MODULE)
                return 0;

        p_w_picpath.depth = 8;
        p_w_picpath.data = logo->data;

        if (fb_logo.needs_cmapreset)
                fb_set_logocmap(info, logo);

        if (fb_logo.needs_truepalette ||
            fb_logo.needs_directpalette) {
                palette = kmalloc(256 * 4, GFP_KERNEL);
                if (palette == NULL)
                        return 0;

                if (fb_logo.needs_truepalette)
                        fb_set_logo_truepalette(info, logo, palette);
                else
                        fb_set_logo_directpalette(info, logo, palette);

                saved_pseudo_palette = info->pseudo_palette;
                info->pseudo_palette = palette;
        }

        if (fb_logo.depth <= 4) {
                logo_new = kmalloc(logo->width * logo->height, GFP_KERNEL);
                if (logo_new == NULL) {
                        kfree(palette);
                        if (saved_pseudo_palette)
                                info->pseudo_palette = saved_pseudo_palette;
                        return 0;
                }
                p_w_picpath.data = logo_new;
                fb_set_logo(info, logo, logo_new, fb_logo.depth);
        }

        p_w_picpath.dx = 0;
        p_w_picpath.dy = y;
        p_w_picpath.width = logo->width;
        p_w_picpath.height = logo->height;

        if (rotate) {
                logo_rotate = kmalloc(logo->width *
                                      logo->height, GFP_KERNEL);
                if (logo_rotate)
                        fb_rotate_logo(info, logo_rotate, &p_w_picpath, rotate);
        }

        fb_do_show_logo(info, &p_w_picpath, rotate, n);

        kfree(palette);
        if (saved_pseudo_palette != NULL)
                info->pseudo_palette = saved_pseudo_palette;
        kfree(logo_new);
        kfree(logo_rotate);
        return logo->height;
}

        参数logo指向了前面所准备的第一个开机画面的内容。这个函数首先根据参数logo的内容来构造一个fb_p_w_picpath结构体p_w_picpath，用来描述最终要显示的第一个开机画面。最后就调用函数fb_do_show_logo来真正执行渲染第一个开机画面的操作。 函数fbcon_switch实现在文件kernel/goldfish/drivers/video/console/fbcon.c中，显示第一个开机画面的过程如下所示：

static void fb_do_show_logo(struct fb_info *info, struct fb_p_w_picpath *p_w_picpath,
                            int rotate, unsigned int num)
{
        unsigned int x;

        if (rotate == FB_ROTATE_UR) {
                for (x = 0;
                     x < num && p_w_picpath->dx + p_w_picpath->width <= info->var.xres;
                     x++) {
                        info->fbops->fb_p_w_picpathblit(info, p_w_picpath);
                        p_w_picpath->dx += p_w_picpath->width + 8;
                }
        } else if (rotate == FB_ROTATE_UD) {
                for (x = 0; x < num && p_w_picpath->dx >= 0; x++) {
                        info->fbops->fb_p_w_picpathblit(info, p_w_picpath);
                        p_w_picpath->dx -= p_w_picpath->width + 8;
                }
        } else if (rotate == FB_ROTATE_CW) {
                for (x = 0;
                     x < num && p_w_picpath->dy + p_w_picpath->height <= info->var.yres;
                     x++) {
                        info->fbops->fb_p_w_picpathblit(info, p_w_picpath);
                        p_w_picpath->dy += p_w_picpath->height + 8;
                }
        } else if (rotate == FB_ROTATE_CCW) {
                for (x = 0; x < num && p_w_picpath->dy >= 0; x++) {
                        info->fbops->fb_p_w_picpathblit(info, p_w_picpath);
                        p_w_picpath->dy -= p_w_picpath->height + 8;
                }
        }
}

       参数rotate用来描述屏幕的当前旋转方向。屏幕旋转方向不同，第一个开机画面的渲染方式也有所不同。例如，当屏幕上下颠倒时（FB_ROTATE_UD），第一个开机画面的左右顺序就刚好调换过来，这时候就需要从右到左来渲染。其它三个方向FB_ROTATE_UR、FB_ROTATE_CW和FB_ROTATE_CCW分别表示没有旋转、顺时针旋转90度和逆时针旋转90度。

 

       参数info用来描述要渲染的帧缓冲区硬件设备，它的成员变量fbops指向了一系列回调函数，用来操作帧缓冲区硬件设备，其中，回调函数fb_p_w_picpathblit就是用来在指定的帧缓冲区硬件设备渲染指定的图像的。

       至此，第一个开机画面的显示过程就分析完成了。