官方的XCB文档告诉我们using OpenGL purely with XCB is impossible：一个人也必须使用Xlib.
巴特梅西(XCB的创始人)This post并未暗示这应该是不可能的.但我确定我错过了一些东西.
我花了好几个小时浏览xcb / glx.h,它组织得很好here.在我看来,它就像一个完整的API.但我无法让它发挥作用.
问题
> XCB / GLX API无用吗？ xcb / glx.h的目的是什么？
>如何使用API？
(注意：这是了解XCB如何工作的持续努力的一部分.)
相关SO thread.
次要的,啰嗦的东西
如果有人愿意采取行动,这里是来自XCB邮件列表中原始帖子的来源,删除了一点并放入一个文件中.
您会注意到xcb_glx_make_context_current返回错误169(不知道这意味着什么),但前提是xcb_glx_create_window为其最后两个参数取0和NULL.这些参数涉及一系列属性,它们似乎是由函数xcb_glx_create_window_attribs返回的,但我无法弄清楚如何使用它…
int main()之前的长辅助函数仅表示两个返回两个整数xcb_glx_fbconfig_t fbconfig xcb_visualid_t glx_visual,对应于第一个“匹配”帧缓冲配置.在我的平台上,这些是0xa7和0x24.它们正是Xlib / GLX例程(实际工作)返回的原因,所以我知道我选择的帧缓冲配置很好.
所以,问题似乎发生在xcb_glx_create_window和xcb_glx_make_context_current之间…
// gcc main2.c -o main -lxcb -lxcb-glx -lGL && ./main2
// TODO free replies
#include <stdio.h>
#include <stdlib.h>
#include <xcb/glx.h>
#include <GL/gl.h>
#define W 1024
#define H 1024
// parameter types returned by xcb_glx_get_fb_configs
#define GLX_DRAWABLE_TYPE 0x8010
#define GLX_RENDER_TYPE 0x8011
#define GLX_DOUBLEBUFFER 5
#define GLX_RED_SIZE 8
#define GLX_GREEN_SIZE 9
#define GLX_BLUE_SIZE 10
#define GLX_RGBA_BIT 0x00000001
#define GLX_RGBA_TYPE 0x8014
#define GLX_STENCIL_SIZE 13
#define GLX_DEPTH_SIZE 12
#define GLX_BUFFER_SIZE 2
#define GLX_ALPHA_SIZE 11
#define GLX_X_RENDERABLE 0x8012
#define GLX_FBCONFIG_ID 0x8013
#define GLX_VISUAL_ID 0x800b
#define GLX_WINDOW_BIT 0x00000001
#define GLX_PIXMAP_BIT 0x00000002
#define GLX_PBUFFER_BIT 0x00000004
// ------------------------------------------------------------------------------------------------
// fbconfig and visual?
uint32_t glx_attrs[] = {
GLX_DOUBLEBUFFER, 1,
GLX_DRAWABLE_TYPE, GLX_WINDOW_BIT|GLX_PIXMAP_BIT|GLX_PBUFFER_BIT,
GLX_X_RENDERABLE, 1,
GLX_RED_SIZE, 8,
GLX_GREEN_SIZE, 8,
GLX_BLUE_SIZE, 8,
GLX_ALPHA_SIZE, 8,
GLX_STENCIL_SIZE, 8,
GLX_DEPTH_SIZE, 24,
GLX_BUFFER_SIZE, 32,
GLX_RENDER_TYPE, GLX_RGBA_BIT,
};
// ------------------------------------------------------------------------------------------------
// This function searches for an @param prop_name in the @param property list of properties of size @param prop. Prop is property count and not buffer size.
uint32_t glx_get_property(const uint32_t* property, const uint props, uint32_t prop_name){
uint i=0;
while(i < props*2){
if(property[i] == prop_name)
return property[i+1];
else i += 2;
}
return -1;
}
// This function chooses and returns specific fbconfig id depending on attributes specified in
// @param attrib list. @param attribsz is the number of properties(not list size)
int32_t glx_choose_fbconfig(xcb_connection_t* connection, uint32_t screen_num, uint32_t* attrib, uint32_t attribsz){
xcb_generic_error_t* xerror;
xcb_glx_get_fb_configs_reply_t* fbconfigs = xcb_glx_get_fb_configs_reply(connection, xcb_glx_get_fb_configs(connection, screen_num), NULL);
uint32_t* prop = xcb_glx_get_fb_configs_property_list(fbconfigs);
uint32_t* fbconfig_line = prop;
uint32_t fbconfig_linesz = fbconfigs->num_properties * 2;
for(uint i=0 ; i<fbconfigs->num_FB_configs; i++){ // for each fbconfig line
uint good_fbconfig = 1;
for(uint j=0 ; j<attribsz*2; j += 2){ // for each attrib
// if property found != property given
if(glx_get_property(fbconfig_line, fbconfigs->num_properties, attrib[j]) != attrib[j+1]) {
good_fbconfig = 0; // invalidate this fbconfig entry, sine one of the attribs doesn't match
break;
}
}
// if all attribs matched, return with fid
if(good_fbconfig){
uint32_t fbconfig_id = glx_get_property(fbconfig_line, fbconfigs->num_properties , GLX_FBCONFIG_ID);
free(fbconfigs);
return fbconfig_id;
}
fbconfig_line += fbconfig_linesz; // next fbconfig line;
}
return -1;
}
// This function returns @param attrib value from a line containing GLX_FBCONFIG_ID of @param fid
// It kind of queries particular fbconfig line for a specific property.
uint32_t glx_get_attrib_from_fbconfig(xcb_connection_t* connection, uint32_t screen_num, uint32_t fid, uint32_t attrib){
xcb_glx_get_fb_configs_reply_t* fbconfigs = xcb_glx_get_fb_configs_reply(connection, xcb_glx_get_fb_configs(connection, screen_num), NULL);
uint32_t* prop = xcb_glx_get_fb_configs_property_list(fbconfigs);
uint i = 0;
uint fid_found = 0;
while(i < fbconfigs->length){
if(prop[i] == GLX_FBCONFIG_ID) {
if(prop[i+1] == fid){
fid_found = 1;
i -= i%(fbconfigs->num_properties * 2); // going to start of the fbconfig line
uint32_t attrib_value = glx_get_property(&prop[i], fbconfigs->num_properties, attrib);
free(fbconfigs);
return attrib_value;
}
}
i+=2;
}
if(fid_found) printf("glx_get_attrib_from_fbconfig: no attrib %u was found in a fbconfig with GLX_FBCONFIG_ID %u\n", attrib, fid);
else printf("glx_get_attrib_from_fbconfig: GLX_FBCONFIG_ID %u was not found!\n", fid);
return -1;
}
// ------------------------------------------------------------------------------------------------
int main(){
xcb_generic_error_t* xerror; // To hold errors!
int screen_number;
xcb_connection_t* connection = xcb_connect(NULL, &screen_number);
xcb_screen_t* screen = xcb_setup_roots_iterator(xcb_get_setup(connection)).data; // getting the default screen
printf("screen %d root %d\n", screen_number, screen->root);
xcb_colormap_t colormap = xcb_generate_id(connection); // generating XID's for our objects!
xcb_window_t window = xcb_generate_id(connection);
xcb_glx_context_t glx_context = xcb_generate_id(connection);
xcb_glx_window_t glx_window = xcb_generate_id(connection);
// ----------------------------------------------------------------------------------------------
xcb_glx_query_version_reply_t* glx_version = xcb_glx_query_version_reply(connection, xcb_glx_query_version(connection, 0, 0), NULL);
printf("glx %d.%d response_type %x pad0 %x sequence %x length %d\n",
glx_version->major_version, glx_version->minor_version, glx_version->response_type,
glx_version->pad0, glx_version->sequence, glx_version->length);
// ----------------------------------------------------------------------------------------------
xcb_glx_fbconfig_t fbconfig = glx_choose_fbconfig(connection, screen_number, glx_attrs, sizeof(glx_attrs)/2/sizeof(uint32_t));
xcb_visualid_t glx_visual = glx_get_attrib_from_fbconfig(connection, screen_number, fbconfig, GLX_VISUAL_ID);
printf("fbconfig %x glx_visual %x\n", fbconfig, glx_visual);
// ----------------------------------------------------------------------------------------------
xcb_glx_create_new_context(connection, glx_context, fbconfig, screen_number, GLX_RGBA_TYPE, 0, 1); // New-style context?
// xcb_glx_create_context(connection, glx_context, glx_visual, 0, 0, 1); // Alt method! Old-style context?
if(!(xcb_glx_is_direct_reply(connection, xcb_glx_is_direct(connection, glx_context), NULL)->is_direct))
puts("glx context is not direct!");
// ----------------------------------------------------------------------------------------------
xcb_create_colormap(connection , XCB_COLORMAP_ALLOC_NONE, colormap, screen->root, glx_visual); // creating colormap
// creating a window, using our new colormap
uint32_t window_mask = XCB_CW_BACK_PIXEL|XCB_CW_EVENT_MASK|XCB_CW_COLORMAP;
uint32_t window_attrs[] = {0x444444, XCB_EVENT_MASK_EXPOSURE|XCB_EVENT_MASK_KEY_PRESS, colormap};
xcb_create_window(connection, screen->root_depth, window, screen->root, 0,0, W,H, 0, XCB_WINDOW_CLASS_INPUT_OUTPUT, glx_visual, window_mask, window_attrs);
xcb_map_window(connection, window);
xcb_glx_create_window(connection, screen_number, fbconfig, window, glx_window, 0, NULL);
xcb_flush(connection);
// ----------------------------------------------------------------------------------------------
xcb_glx_make_context_current_reply_t* reply_ctx = xcb_glx_make_context_current_reply(connection, xcb_glx_make_context_current(connection, 0, glx_window, glx_window, glx_context), NULL);
if(!reply_ctx) puts("ERROR xcb_glx_make_context_current returned NULL!");
xcb_glx_context_tag_t glx_context_tag = reply_ctx->context_tag;
// alternative ?
// xcb_glx_make_current_reply_t* reply_mc = xcb_glx_make_current_reply(connection, xcb_glx_make_current(connection, glx_window, glx_context, 0), NULL);
// xcb_glx_context_tag_t glx_context_tag = reply_mc->context_tag;
// ----------------------------------------------------------------------------------------------
xcb_glx_get_error_reply(connection, xcb_glx_get_error(connection, glx_context_tag), &xerror);
if(xerror) printf("\nERROR xcb_glx_get_error %d\n", xerror->error_code);
// ----------------------------------------------------------------------------------------------
xcb_generic_event_t* event;
uint running = 1;
while(running){
event = xcb_poll_for_event(connection);
if(event){
switch (event->response_type) {
case XCB_EXPOSE:
glClearColor(0, .5, 1, 1); // Blue
glFlush();
xcb_glx_swap_buffers(connection, glx_context_tag, glx_window);
puts("Expose!");
break;
case XCB_KEY_PRESS: // exit on key press
running = 0;
break;
}
}
free(event);
}
xcb_disconnect(connection);
}
解决方法:
这里需要了解的重要事项是XCB函数直接映射到X11协议请求.这意味着xcb_glx_ *函数直接映射到X11 GLX协议请求.请参阅https://www.khronos.org/registry/OpenGL/specs/gl/glx1.4.pdf中的“第4章”.它列出了所有可用的GLX请求.例如,glAreTexturesResident从xcb / glx.h(https://xcb.freedesktop.org/manual/glx_8h_source.html)映射到xcb_glx_are_textures_resident_ * API.在Khronos规范中,您可以阅读请求做什么.
What’s the purpose of xcb/glx.h?
XCB-GLX只与X服务器通信,它不执行任何硬件初始化或触摸OpenGL客户端状态.因此,XCB-GLX不能用作GLX API的替代品. [1]
硬件初始化和其他GL内容由openGL lib完成.这就是规范的“另一半”实施的地方.在Linux上,libsa由mesa(https://cgit.freedesktop.org/mesa/mesa/tree/src/glx)提供.你可以看到glx目录中的文件包含Xlib.h,所以我想这就是Xlib依赖的来源.这解释了“GLX API与Xlib紧密结合.因此,X Windows上的OpenGL应用程序必须使用Xlib,因此不能仅使用XCB.” [1].
Is the XCB/GLX API useless?
虽然XCB-GLX API对最终用户XCB应用程序开发人员没什么价值,但它可以用于开发基于XCB的新OpenGL和GLX实现. XCB可以提高OpenGL库的速度和质量. [1]
因此,为了获得纯XCB GLX,有人需要在openGL lib中重新实现GLX：
>公开基于XCB的API以初始化硬件等.
>应该使用xcb_glx API与X服务器进行通信,而不是Xlib.
来自[1]的文档说“GLX系统有两个角色,它与X服务器通信并初始化客户端和硬件状态.”
xcb-glx负责沟通.另一个角色(基于XCB的OpenGL和GLX实现)目前尚未实现,也不太可能实现.
“GLX API是根据Xlib指定的,glX函数使用Xlib Displays,Windows,Visuals等.GLX实现也是使用Xlib构建的.” (参见libGL.so的导出符号).为了完成第二个角色,我们需要一个使用XCB连接,窗口,视觉效果的相同API.
[1] https://xcb.freedesktop.org/opengl/
免责声明：这是我对收集的理解.