适用于OpenGL离屏渲染上下文的初始化代码

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

class GLContext
{
public:
class nativeContext;
static nativeContext* init(int version=2);
static void destroy(nativeContext* context);
};

class GLAutoContext
{
public:
GLAutoContext()
        {
            mContext = GLContext::init();
        }
        ~GLAutoContext()
        {
            GLContext::destroy(mContext);
        }
private:
        GLContext::nativeContext* mContext;
};

cpp文件

#include "GL/GLContext.h"
#include <assert.h>

#ifdef GL_BUILD_FOR_ANDROID
#include <EGL/egl.h>
class GLContext::nativeContext
{
 public:
 nativeContext()
 {
 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, 2,
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);
 }
 ~nativeContext()
 {
 eglMakeCurrent(gDisplay, EGL_NO_SURFACE , EGL_NO_SURFACE , EGL_NO_CONTEXT);
 eglDestroyContext(gDisplay, gContext);
 eglDestroySurface(gDisplay, gSurface);
 eglTerminate(gDisplay);
 gDisplay = EGL_NO_DISPLAY;
 }

 private:
EGLContext gContext;
EGLDisplay gDisplay;
EGLSurface gSurface;
};
#else
#ifdef __APPLE__
#include <OpenGL/OpenGL.h>
class GLContext::nativeContext
{
 public:
 nativeContext()
 {
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);
 }
 ~nativeContext()
 {
CGLReleaseContext(gContext);
 }
 private:
CGLContextObj gContext;
};
#else
#include <GL/glew.h>
#include <GL/glut.h>
#include <X11/Xlib.h>
#include <GL/glx.h>
class GLContext::nativeContext
{
 public:
 nativeContext()
 {
 gDisplay = XOpenDisplay(0);
 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();
 }
 ~nativeContext()
 {
 glXMakeCurrent(gDisplay, 0,0);
 glXDestroyContext(gDisplay, gContext);
 glXDestroyGLXPixmap(gDisplay, gGlxPixmap);
XFreePixmap(gDisplay, gPixmap);
XCloseDisplay(gDisplay);
 gDisplay = NULL;
 }
 private:
GLXContext gContext;
Pixmap gPixmap;
GLXPixmap gGlxPixmap;
Display* gDisplay;
};
#endif
#endif


GLContext::nativeContext* GLContext::init(int version)
{
 return new nativeContext;
}

void GLContext::destroy(nativeContext* context)
{
 delete context;
}