如何使用 GLX 创建“核心”OpenGL 上下文？

Question

我想使用带有“核心”配置文件的 GLX 创建一个 OpenGL 上下文。

为了比较起见，QOpenGLContext 可以用QGLFormat::CoreProfile 创建。

我找到了这些说明：Creating a modern OpenGL context，但我没有看到核心/兼容性配置文件的提及。

/* gcc this.c -lGL -lX11 */

#include <stdbool.h>
#include <stdio.h>
#include <stdlib.h>
#include <GL/glx.h>
#include <X11/Xlib.h>

/*
    License: Public domain

    Contents
    --------
    - Create_display_and_window
    - Create_the_modern_OpenGL_context
    - Show_the_window
    - Application_loop
*/

typedef GLXContext (*glXCreateContextAttribsARBProc)
    (Display*, GLXFBConfig, GLXContext, Bool, const int*);

int main()
{
    Display* disp = 0;
    Window win = 0;

    /* Create_display_and_window
       -------------------------
       Skip if you already have a display and window */
    disp = XOpenDisplay(0);
    win = XCreateSimpleWindow(disp, DefaultRootWindow(disp),
                              10, 10,   /* x, y */
                              800, 600, /* width, height */
                              0, 0,     /* border_width, border */
                              0);       /* background */

    /* Create_the_modern_OpenGL_context
       -------------------------------- */
    static int visual_attribs[] = {
        GLX_RENDER_TYPE, GLX_RGBA_BIT,
        GLX_DRAWABLE_TYPE, GLX_WINDOW_BIT,
        GLX_DOUBLEBUFFER, true,
        GLX_RED_SIZE, 1,
        GLX_GREEN_SIZE, 1,
        GLX_BLUE_SIZE, 1,
        None
    };

    int num_fbc = 0;
    GLXFBConfig *fbc = glXChooseFBConfig(disp,
                                         DefaultScreen(disp),
                                         visual_attribs, &num_fbc);
    if (!fbc) {
        printf("glXChooseFBConfig() failed\n");
        exit(1);
    }

    /* If we were on Windows (i.e. WGL), we would need to create an old
       dummy OpenGL context here, before calling GetProcAddress(). This is
       unnecessary on Linux (GLX).

       For details, refer to the spec
       (https://www.khronos.org/registry/OpenGL/extensions/ARB/GLX_ARB_get_proc_address.txt)
       which says:
           > Are function pointers context-independent? Yes. The pointer to an
           > extension function can be used with any context [...]

       This is in direct contrast to WGL's wglGetProcAddress. */

    glXCreateContextAttribsARBProc glXCreateContextAttribsARB = 0;
    glXCreateContextAttribsARB =
        (glXCreateContextAttribsARBProc)
        glXGetProcAddress((const GLubyte*)"glXCreateContextAttribsARB");

    /* If we were on Winows, we would destroy the dummy context here. Again,
       this is unnecessary on Linux.*/

    if (!glXCreateContextAttribsARB) {
        printf("glXCreateContextAttribsARB() not found\n");
        exit(1);
    }

    /* Set desired minimum OpenGL version */
    static int context_attribs[] = {
        GLX_CONTEXT_MAJOR_VERSION_ARB, 4,
        GLX_CONTEXT_MINOR_VERSION_ARB, 2,
        None
    };
    /* Create modern OpenGL context */
    GLXContext ctx = glXCreateContextAttribsARB(disp, fbc[0], NULL, true,
                                                context_attribs);
    if (!ctx) {
        printf("Failed to create OpenGL context. Exiting.\n");
        exit(1);
    }

    /* Show_the_window
       --------------- */
    XMapWindow(disp, win);
    glXMakeCurrent(disp, win, ctx);

    int major = 0, minor = 0;
    glGetIntegerv(GL_MAJOR_VERSION, &major);
    glGetIntegerv(GL_MINOR_VERSION, &minor);
    printf("OpenGL context created.\nVersion %d.%d\nVendor %s\nRenderer %s\n",
           major, minor,
           glGetString(GL_VENDOR),
           glGetString(GL_RENDERER));

    /* Application_loop
       ---------------- */
    while(1) {}

    return 0;
}

khronos.org documentation 说

您可以使用此查询检测上下文支持的配置文件：

glGetIntegerv(GL_CONTEXT_PROFILE_MASK, *);

这可以包含位 GL_CONTEXT_CORE_PROFILE_BIT 或 GL_CONTEXT_COMPATIBILITY_PROFILE_BIT，但不能同时包含两者。

但这是在查询已经创建的上下文的功能。

如何使用 GLX 创建核心上下文？

Answer 1

您的context_attribs 应包含GLX_CONTEXT_PROFILE_MASK_ARB 参数（如此答案GLX Context Creation Error: GLXBadFBConfig）：

    static int context_attribs[] = {
        GLX_CONTEXT_MAJOR_VERSION_ARB, 4,
        GLX_CONTEXT_MINOR_VERSION_ARB, 2,
        GLX_CONTEXT_PROFILE_MASK_ARB,  GLX_CONTEXT_CORE_PROFILE_BIT_ARB,
        None
    };

    GLXContext ctx = glXCreateContextAttribsARB(disp, fbc[0], NULL, true,
                                                context_attribs);