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。

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