我正在开发一个已经在使用xcb的项目，需要获得单个输出的分辨率而不是组合屏幕的分辨率。我可以用xcb的RandR扩展吗？如果是这样，我如何使用xcb_connection_t对象来执行此操作。
答案 0 :(得分：7)
我也在寻找答案。我不知道你是否成功，但由于你还没有回答这个问题，我猜你没有。
对于那些正在寻找如何做到这一点的人，您必须了解XCB的工作原理。它对RandR XCB扩展特别重要。您可能知道要从X服务器获取一些信息，您需要先使用请求进行查询。如果在发送请求后XCB，您将收到 Cookie ，其中存储已发送请求的 ID 。你为什么需要这样的饼干？原因很简单而且很明显 - 要从X服务器获得回复，我们需要使用我们发送的请求的ID来询问它（因此服务器知道您想要答案的请求）。
为了让它更清晰，这是日常生活中的一个简单例子 - 想象一个记忆极短的调酒师，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不会一次发送请求并得到答案呢？嗯，这正是Xlib的工作原理，事实证明，在某些条件下，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？这是我如何做的最小化版本：
#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;
}
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
如果你想要的话，你可以用vector来改善代码的可读性，而不是使用指针进行动态分配，但我不认为这很难理解。
我还不熟悉XCB编程，并且PROBABLY是一种更好的方法，但这种方法看起来并不坏。我花了很多时间试图理解这一点，所以我希望它会对某人有所帮助。
有用的链接：