我正在一个已经在使用xcb的项目中，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扩展名吗？如果是这样，我该如何使用xcb_connection_t对象执行此操作。
最佳答案
我也在寻找答案。我不知道您是否成功，但是由于您尚未回答此问题，所以我想您还没有成功。
对于那些正在寻找如何执行此操作的人，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。您可能知道要从X服务器获取一些信息，您首先需要使用请求对其进行查询。在发送请求后使用XCB的情况下，您将获得一个 cookie ，其中存储了已发送请求的 ID 。为什么需要这样的cookie？原因很简单而且很明显-要从X服务器获得答复，我们需要使用我们已发送的请求ID来请求它(以便服务器知道您想要答案的请求)。
为了更清楚一点，这里是日常生活中的一个简单示例-想象一下一个调酒师的内存力非常短，所以它像这样:
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，为什么XCB不能简单地一次发送请求并获得答案呢？好吧，这正是Xlib的工作方式，事实证明，在某些情况下XCB的速度提高了117倍。如果您想了解更多信息，请阅读XCB教程中的Basic XCB Notions。
回到问题-如何获得输出(或更确切地说是CRTC)的分辨率？这是我的操作的最小化版本:
#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;
}
输出示例:
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
如果愿意，可以使用vector和诸如此类的方法来提高代码的可读性，而不是使用带有指针的动态分配，但是我认为这并不难理解。
我还是XCB编程的新手，那里的PROBABLY是更好的方法，但是这种方法似乎一点也不差。我花了大量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:
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/