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说明

最近做图像算法，需要用到shader对图像进行处理，用glut会有窗口，不适合写成UT测试用例，需要创建一个无窗口的OpenGL上下文。

代码

这部分代码其实是参考 Android的Skia 模块相关代码写的，适用于 Mac、EGL（Android）、X11（Ubuntu等Linux系统）平台。

h文件

#ifndef GL_GLCONTEXT_H
#define GL_GLCONTEXT_H
class GLContext {public:static bool init(int version=2);static void destroy();
};
#endif

cpp文件

#include "GL/GLContext.h"
#include <assert.h>#ifdef GL_BUILD_FOR_ANDROID
//适用于 Android 和其他使用 EGL 标准的平台
#include <EGL/egl.h>
static EGLContext gContext;
static EGLDisplay gDisplay;
static EGLSurface gSurface;
bool GLContext::init(int version)
{gDisplay = eglGetDisplay(EGL_DEFAULT_DISPLAY);EGLint majorVersion;EGLint minorVersion;eglInitialize(gDisplay, &majorVersion, &minorVersion);EGLint numConfigs;static const EGLint configAttribs[] = {EGL_SURFACE_TYPE, EGL_PBUFFER_BIT,EGL_RENDERABLE_TYPE, EGL_OPENGL_ES2_BIT,EGL_RED_SIZE, 8,EGL_GREEN_SIZE, 8,EGL_BLUE_SIZE, 8,EGL_ALPHA_SIZE, 8,EGL_NONE};EGLConfig surfaceConfig;eglChooseConfig(gDisplay, configAttribs, &surfaceConfig, 1, &numConfigs);static const EGLint contextAttribs[] = {EGL_CONTEXT_CLIENT_VERSION, version,EGL_NONE};gContext = eglCreateContext(gDisplay, surfaceConfig, NULL, contextAttribs);static const EGLint surfaceAttribs[] = {EGL_WIDTH, 1,EGL_HEIGHT, 1,EGL_NONE};gSurface = eglCreatePbufferSurface(gDisplay, surfaceConfig, surfaceAttribs);eglMakeCurrent(gDisplay, gSurface, gSurface, gContext);return true;
}void GLContext::destroy()
{eglMakeCurrent(gDisplay, EGL_NO_SURFACE , EGL_NO_SURFACE , EGL_NO_CONTEXT);eglDestroyContext(gDisplay, gContext);eglDestroySurface(gDisplay, gSurface);eglTerminate(gDisplay);gDisplay = EGL_NO_DISPLAY;
}
#else
/*适用于Mac平台*/
#ifdef __APPLE__
#include <OpenGL/OpenGL.h>
CGLContextObj gContext;
bool GLContext::init(int version)
{CGLPixelFormatAttribute attributes[] = {kCGLPFADoubleBuffer,(CGLPixelFormatAttribute)0};CGLPixelFormatObj pixFormat;GLint npix;CGLChoosePixelFormat(attributes, &pixFormat, &npix);assert(NULL!=pixFormat);CGLCreateContext(pixFormat, NULL, &gContext);CGLReleasePixelFormat(pixFormat);assert(NULL!=gContext);CGLSetCurrentContext(gContext);return true;
}
void GLContext::destroy()
{CGLReleaseContext(gContext);
}
#else
/*这个是以前用在Ubuntu系统中的，使用了glew以打开shader功能，适用于 XDisplay*/
#include <GL/glew.h>
#include <GL/glut.h>
#include <X11/Xlib.h>
#include <GL/glx.h>
static GLXContext gContext;
static Pixmap gPixmap;
static GLXPixmap gGlxPixmap;
static Display* gDisplay = XOpenDisplay(0);
bool GLContext::init(int version)
{int fbcount;static int visual_attribs[] = {GLX_X_RENDERABLE    , True,GLX_DRAWABLE_TYPE   , GLX_PIXMAP_BIT,None};GLXFBConfig *fbc = glXChooseFBConfig(gDisplay, DefaultScreen(gDisplay),visual_attribs, &fbcount);int best_fbc = -1, best_num_samp = -1;int i;for (i = 0; i < fbcount; ++i) {XVisualInfo *vi = glXGetVisualFromFBConfig(gDisplay, fbc[i]);if (vi) {int samp_buf, samples;glXGetFBConfigAttrib(gDisplay, fbc[i], GLX_SAMPLE_BUFFERS, &samp_buf);glXGetFBConfigAttrib(gDisplay, fbc[i], GLX_SAMPLES, &samples);if (best_fbc < 0 || (samp_buf && samples > best_num_samp))best_fbc = i, best_num_samp = samples;}XFree(vi);}GLXFBConfig bestFbc = fbc[best_fbc];XFree(fbc);XVisualInfo *vi = glXGetVisualFromFBConfig(gDisplay, bestFbc);gPixmap = XCreatePixmap(gDisplay, RootWindow(gDisplay, vi->screen), 10, 10, vi->depth);gGlxPixmap = glXCreateGLXPixmap(gDisplay, vi, gPixmap);XFree(vi);gContext = glXCreateNewContext(gDisplay, bestFbc, GLX_RGBA_TYPE, 0, True);glXMakeCurrent(gDisplay, gGlxPixmap, gContext);glewInit();return true;
}void GLContext::destroy()
{glXMakeCurrent(gDisplay, 0,0);glXDestroyContext(gDisplay, gContext);glXDestroyGLXPixmap(gDisplay, gGlxPixmap);XFreePixmap(gDisplay, gPixmap);gDisplay = NULL;XCloseDisplay(gDisplay);
}
#endif
#endif

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