Android系統的開機畫面顯示過程分析（4）

        函數fb_show_logo_line也是實如今文件kernel/goldfish/drivers/video/fbmem.c中，以下所示：

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;
}

        參數logo指向了前面所準備的第一個開機畫面的內容。這個函數首先根據參數logo的內容來構造一個fb_p_w_picpath結構體p_w_picpath，用來描述最終要顯示的第一個開機畫面。最後就調用函數fb_do_show_logo來真正執行渲染第一個開機畫面的操做。 函數fbcon_switch實如今文件kernel/goldfish/drivers/video/console/fbcon.c中，顯示第一個開機畫面的過程以下所示：

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;
                }
        }
}

       參數rotate用來描述屏幕的當前旋轉方向。屏幕旋轉方向不一樣，第一個開機畫面的渲染方式也有所不一樣。例如，當屏幕上下顛倒時（FB_ROTATE_UD），第一個開機畫面的左右順序就恰好調換過來，這時候就須要從右到左來渲染。其它三個方向FB_ROTATE_UR、FB_ROTATE_CW和FB_ROTATE_CCW分別表示沒有旋轉、順時針旋轉90度和逆時針旋轉90度。

 

       參數info用來描述要渲染的幀緩衝區硬件設備，它的成員變量fbops指向了一系列回調函數，用來操做幀緩衝區硬件設備，其中，回調函數fb_p_w_picpathblit就是用來在指定的幀緩衝區硬件設備渲染指定的圖像的。

       至此，第一個開機畫面的顯示過程就分析完成了。