我正在处理一个已经在使用 xcb 的项目,并且需要获得单个输出的分辨率而不是组合屏幕的分辨率。我可以使用 xcb 的 RandR 扩展来做到这一点吗?如果是这样,我如何使用我的 xcb_connection_t
对象来执行此操作。
最佳答案
我也在寻找答案。我不知道你有没有成功,但既然你没有回答这个问题,我想你没有。
对于那些正在寻找如何做到这一点的人,您必须了解 XCB 通常是如何工作的。这对于 RandR XCB 扩展尤为重要。正如您可能知道的那样,要从 X 服务器获取一些信息,您需要先使用请求 查询它。对于 XCB,在发送请求后,您将获得一个 cookie,其中存储已发送请求的 ID。你为什么需要这样的cookie?原因很简单也很明显——要从 X 服务器获得一个回复,我们需要用我们发送的请求的 ID 来请求它(这样服务器就知道你想要哪个请求的答案)。
为了更清楚地说明,这里举一个日常生活中的简单例子 - 想象一个内存力极差的调酒师,所以它是这样的:
client : "I'd like to order a beer."
bartender: "OK, I'll get you a beer."
*bartender handles a ticket with an ID of the beer order to the client*
*client waits and waits and then he approaches bartender*
client : "Dude, give me my beer finally, here's your damn ticket"
*client handles the ticket to bartender, who looks for the order from the
ticket in his order book and when he finds it he replies*
bartender: "Here's your beer, enjoy."
好的,那么为什么 XCB 不简单地发送请求并一次性获得答复呢?好吧,这正是 Xlib 的工作原理,事实证明,在某些情况下,XCB 的速度提高了 117 倍。请阅读Basic XCB Notions如果您想了解更多信息,请参阅 XCB 教程。
回到问题 - 如何获得输出(或更确切地说是 CRTC)的分辨率?这是我如何操作的简化版本:
#include <cstdio>
#include <xcb/xcb.h>
#include <xcb/randr.h>
int main()
{
//Open connection to X server
xcb_connection_t* XConnection = xcb_connect(0, 0);
//Get the first X screen
xcb_screen_t* XFirstScreen = xcb_setup_roots_iterator(
xcb_get_setup(XConnection)).data;
//Generate ID for the X window
xcb_window_t XWindowDummy = xcb_generate_id(XConnection);
//Create dummy X window
xcb_create_window(XConnection, 0, XWindowDummy, XFirstScreen->root,
0, 0, 1, 1, 0, 0, 0, 0, 0);
//Flush pending requests to the X server
xcb_flush(XConnection);
//Send a request for screen resources to the X server
xcb_randr_get_screen_resources_cookie_t screenResCookie = {};
screenResCookie = xcb_randr_get_screen_resources(XConnection,
XWindowDummy);
//Receive reply from X server
xcb_randr_get_screen_resources_reply_t* screenResReply = {};
screenResReply = xcb_randr_get_screen_resources_reply(XConnection,
screenResCookie, 0);
int crtcs_num = 0;
xcb_randr_crtc_t* firstCRTC;
//Get a pointer to the first CRTC and number of CRTCs
//It is crucial to notice that you are in fact getting
//an array with firstCRTC being the first element of
//this array and crtcs_length - length of this array
if(screenResReply)
{
crtcs_num = xcb_randr_get_screen_resources_crtcs_length(screenResReply);
firstCRTC = xcb_randr_get_screen_resources_crtcs(screenResReply);
}
else
return -1;
//Array of requests to the X server for CRTC info
xcb_randr_get_crtc_info_cookie_t* crtcResCookie = new
xcb_randr_get_crtc_info_cookie_t[crtcs_num];
for(int i = 0; i < crtcs_num; i++)
crtcResCookie[i] = xcb_randr_get_crtc_info(XConnection,
*(firstCRTC+i), 0);
//Array of pointers to replies from X server
xcb_randr_get_crtc_info_reply_t** crtcResReply = new
xcb_randr_get_crtc_info_reply_t*[crtcs_num];
for(int i = 0; i < crtcs_num; i++)
crtcResReply[i] = xcb_randr_get_crtc_info_reply(XConnection,
crtcResCookie[i], 0);
//Self-explanatory
for(int i = 0; i < crtcs_num; i++)
{
if(crtcResReply[i])
{
printf("CRTC[%i] INFO:\n", i);
printf("x-off\t: %i\n", crtcResReply[i]->x);
printf("y-off\t: %i\n", crtcResReply[i]->y);
printf("width\t: %i\n", crtcResReply[i]->width);
printf("height\t: %i\n\n", crtcResReply[i]->height);
}
}
xcb_disconnect(XConnection);
return 0;
}
示例输出:
CRTC[0] INFO:
x-off : 1920
y-off : 0
width : 1920
height : 1200
CRTC[1] INFO:
x-off : 0
y-off : 0
width : 1920
height : 1200
CRTC[2] INFO:
x-off : 0
y-off : 0
width : 0
height : 0
CRTC[3] INFO:
x-off : 0
y-off : 0
width : 0
height : 0
如果你想提高代码的可读性,你可以用 vector 之类的东西来代替使用指针动态分配,但我认为这并不难理解。
我对 XCB 编程还是个新手,可能有更好的方法,但这种方法看起来一点也不差。我花了很多时间试图理解这一点,所以我希望它能对某人有所帮助。
有用的链接:
- XCB Tutorial (建议自己找路)
- XCB API (非常有用,在这种情况下尤其是 RandR API)
关于c - 如何通过 xcb RandR 扩展获得 RandR 输出的分辨率?,我们在Stack Overflow上找到一个类似的问题: https://stackoverflow.com/questions/22108822/