OpenGL绘制一张图片的流程--以android-openGL-canvas为例

样例代码来源: android-openGL-canvas

OpenGL文档参考：
OpenGL文档
本文只对流程做排序以及一些简单的说明，想了解原理的请查看OpenGL相关文档，有对相应函数有疑问的可查阅上述文档。

一、创建 eglContext。EGLContext 是一个比较重的对象，所以一般只创建一次。

例子代码代码主要在 EglHelper

• egl = EGLContext.getEGL()
• 获取 eglDisplay = eglGetDisplay(EGL10.EGL_DEFAULT_DISPLAY)
• 获取 EGLConfig eglChooseConfig(..)
• eglInitialize(mEgl, mEglDisplay, mEglConfig, eglContext)

• 创建 eglContext = eglCreateContext(display, config, eglContext, attrib_list))

• 大致的相关代码

    public EGLContext start(EGLContext eglContext) {
        if (GLThread.LOG_EGL) {
            Log.w("EglHelper", "start() tid=" + Thread.currentThread().getId());
        }
        /*
         * Get an EGL instance
         */
        mEgl = (EGL10) EGLContext.getEGL();

        /*
         * Get to the default display.
         */
        mEglDisplay = mEgl.eglGetDisplay(EGL10.EGL_DEFAULT_DISPLAY);

        if (mEglDisplay == EGL10.EGL_NO_DISPLAY) {
            throw new RuntimeException("eglGetDisplay failed");
        }

        /*
         * We can now initialize EGL for that display
         */
        int[] version = new int[2];
        if (!mEgl.eglInitialize(mEglDisplay, version)) {
            throw new RuntimeException("eglInitialize failed");
        }
        mEglConfig = eglConfigChooser.chooseConfig(mEgl, mEglDisplay);

            /*
            * Create an EGL context. We want to do this as rarely as we can, because an
            * EGL context is a somewhat heavy object.
            */
        mEglContext = eglContextFactory.createContext(mEgl, mEglDisplay, mEglConfig, eglContext);
        if (mEglContext == null || mEglContext == EGL10.EGL_NO_CONTEXT) {
            mEglContext = null;
            throwEglException("createContext");
        }
        if (GLThread.LOG_EGL) {
            Log.w("EglHelper", "createContext " + mEglContext + " tid=" + Thread.currentThread().getId());
        }

        mEglSurface = null;

        return mEglContext;
    }

二、创建 surface

• eglCreateWindowSurface(display, config, nativeWindow, surfaceAttribs)

• 将 context 和 surface 联系起来。
  eglMakeCurrent(eglDisplay, eglSurface, eglSurface, eglContext)

• 如果需要更换surface，就先destroy现在的
  eglDestroySurface

• 大致的相关代码

    public boolean createSurface(Object surface) {