qml中，eglCreatePbufferSurface渲染后，怎么显示出来

在QML中使用OpenGL ES进行渲染可以通过QQuickFramebufferObject类实现。QQuickFramebufferObject是一个QML元素，它允许你通过OpenGL ES渲染，可以将OpenGL ES渲染结果直接显示到QML界面上。

使用QQuickFramebufferObject需要自定义一个QQuickFramebufferObject子类，并实现createFramebufferObject()和Renderer两个函数。其中，createFramebufferObject()函数创建一个QOpenGLFramebufferObject对象，用于渲染，Renderer则负责OpenGL ES渲染。

在实现Renderer时，可以在rendererInitialized()函数中创建Pbuffer表面，将其和OpenGL ES上下文绑定。在render()函数中，可以使用OpenGL ES渲染Pbuffer表面，然后将渲染结果绘制到QOpenGLFramebufferObject对象中。最后，在synchronize()函数中可以将QQuickFramebufferObject元素和OpenGL ES上下文同步，确保渲染结果正确显示。

以下是一个简单的QQuickFramebufferObject子类的示例代码：

import QtQuick 2.0
import QtQuick.Window 2.0
import QtQuick.Controls 2.0
import QtQuick.Scene3D 2.0
import QtQuick.Particles 2.0

Item {
    width: 640
    height: 480

    MyFramebuffer {
        anchors.fill: parent
    }
}

// MyFramebuffer.qml
import QtQuick 2.0
import QtQuick.Window 2.0
import QtQuick.Controls 2.0
import QtQuick.Scene3D 2.0
import QtQuick.Particles 2.0

Item {
    width: 640
    height: 480

    MyFramebufferObject {
        id: fbo
        anchors.fill: parent
    }

    Rectangle {
        anchors.fill: parent
        color: "white"
        opacity: 0.7
    }
}

// MyFramebufferObject.qml
import QtQuick 2.0
import QtQuick.Window 2.0
import QtQuick.Controls 2.0
import QtQuick.Scene3D 2.0
import QtQuick.Particles 2.0
import QtQuick.Controls.Material 2.0
import QtQuick.Controls.impl 2.0

Item {
    width: 640
    height: 480

    property int textureWidth: 512
    property int textureHeight: 512

    // Create Pbuffer surface and OpenGL ES context
    function createFramebufferObject(size) {
        var fbo = new QOpenGLFramebufferObject(size);
        var context = Qt.createQmlObject("import QtQuick 2.0; import QtQuick.Window 2.0; Qt.createQmlObject('Window { visible: false; width: 1; height: 1; visibility: Window.Hidden; }', parent, 'PbufferWindow')");
        var surface = context.createSurface(fbo.handle);
        context.makeCurrent(surface);
        return {fbo: fbo, context: context};
    }

    // Renderer for OpenGL ES
    function MyFramebufferRenderer() {
        var pbufferSurface = null;
        var context = null;
        var program = null;
        var vertexBuffer = null;
        var indexBuffer = null;
        var texture = null;
        var textureLocation = -1;
        var vertexLocation = -1;
        var texCoordLocation = -1;
        var transformLocation = -1;
        var matrix = mat4.create();

        this.rendererInitialized = function() {
            // Create Pbuffer surface and OpenGL ES context
            pbufferSurface = eglCreatePbufferSurface(EGL_DEFAULT_DISPLAY, EGL_NO_CONFIG, [EGL_WIDTH, textureWidth, EGL_HEIGHT, textureHeight, EGL_NONE]);
            context = eglCreateContext(EGL_DEFAULT_DISPLAY, EGL_NO_CONFIG, EGL_NO_CONTEXT, null);
            eglMakeCurrent(EGL_DEFAULT_DISPLAY, pbufferSurface, pbufferSurface, context);

            // Initialize OpenGL ES resources
            program = glCreateProgram();
            var vertexShader = glCreateShader(GL_VERTEX_SHADER);
            var fragmentShader = glCreateShader(GL_FRAGMENT_SHADER);
            glShaderSource(vertexShader, "attribute vec4 vertex; attribute vec2 texCoord; uniform mat4 transform; varying vec2 texCoordVar; void main() { gl_Position = transform * vertex; texCoordVar = texCoord; }");
            glCompileShader(vertexShader);
            glShaderSource(fragmentShader, "precision mediump float; uniform sampler2D texture; varying vec2 texCoordVar; void main() { gl_FragColor = texture2D(texture, texCoordVar); }");
            glCompileShader(fragmentShader);
            glAttachShader(program, vertexShader);
            glAttachShader(program, fragmentShader);
            glLinkProgram(program);
            glUseProgram(program);
            vertexLocation = glGetAttribLocation(program, "vertex");
            texCoordLocation = glGetAttribLocation(program, "texCoord");
            textureLocation = glGetUniformLocation(program, "texture");
            transformLocation = glGetUniformLocation(program, "transform");
            var vertices = new Float32Array([-1.0, -1.0, 0.0, 1.0, 1.0, -1.0, 0.0, 1.0, 1.0, 1.0, 0.0, 1.0, -1.0, 1.0, 0.0, 1.0]);
            var indices = new Uint16Array([0, 1, 2, 0, 2, 3]);
            vertexBuffer = glCreateBuffer();
            glBindBuffer(GL_ARRAY_BUFFER, vertexBuffer);
            glBufferData(GL_ARRAY_BUFFER, vertices, GL_STATIC_DRAW);
            indexBuffer = glCreateBuffer();
            glBindBuffer(GL_ELEMENT_ARRAY_BUFFER, indexBuffer);
            glBufferData(GL_ELEMENT_ARRAY_BUFFER, indices, GL_STATIC_DRAW);
            texture = glCreateTexture();
            glBindTexture(GL_TEXTURE_2D, texture);
            glTexImage2D(GL_TEXTURE_2D, 0, GL_RGBA, textureWidth, textureHeight, 0, GL_RGBA, GL_UNSIGNED_BYTE, null);
            glTexParameteri(GL_TEXTURE_2D, GL_TEXTURE_MIN_FILTER, GL_LINEAR);
            glTexParameteri(GL_TEXTURE_2D, GL_TEXTURE_MAG_FILTER, GL_LINEAR);
            glTexParameteri(GL_TEXTURE_2D, GL_TEXTURE_WRAP_S, GL_CLAMP_TO_EDGE);
            glTexParameteri(GL_TEXTURE_2D, GL_TEXTURE_WRAP_T, GL_CLAMP_TO_EDGE);
        }

        this.render = function() {
            // Render Pbuffer surface
            glViewport(0, 0, textureWidth, textureHeight);
            glClearColor(1.0, 1.0, 1.0, 1.0);
            glClear(GL_COLOR_BUFFER_BIT);
            glBindBuffer(GL_ARRAY_BUFFER, vertexBuffer);
            glEnableVertexAttribArray(vertexLocation);
            glVertexAttribPointer(vertexLocation, 4, GL_FLOAT, false, 0, 0);
            glBindBuffer(GL_ARRAY_BUFFER, 0);
            glBindBuffer(GL_ELEMENT_ARRAY_BUFFER, indexBuffer);
            glEnableVertexAttribArray(texCoordLocation);
            glVertexAttribPointer(texCoordLocation, 2, GL_FLOAT, false, 0, 0);
            glBindBuffer(GL_ELEMENT_ARRAY_BUFFER, 0);
            glUniformMatrix4fv(transformLocation, 1, false, matrix);
            glUniform1i(textureLocation, 0);
            glActiveTexture(GL_TEXTURE0);
            glBindTexture(GL_TEXTURE_2D, texture);
            glDrawElements(GL_TRIANGLES, 6, GL_UNSIGNED_SHORT, 0);
        }

        this.releaseResources = function() {
            // Release OpenGL ES resources
            glDeleteProgram(program);
            glDeleteBuffers(1, [vertexBuffer]);
            glDeleteBuffers(1, [indexBuffer]);
            glDeleteTextures(1, [texture]);
            eglDestroyContext(EGL_DEFAULT_DISPLAY, context);
            eglDestroySurface(EGL_DEFAULT_DISPLAY, pbufferSurface);
        }
    }

    // Create framebuffer object and renderer
    MyFramebufferRenderer.prototype = new QQuickFramebufferObject.Renderer;
    MyFramebufferObject {
        id: myFbo
        width: textureWidth
        height: textureHeight
        antialiasing: true
        textureWidth: 512
        textureHeight: 512
        framebufferObject: createFramebufferObject(Qt.size(textureWidth, textureHeight))
        renderer: MyFramebufferRenderer {}
    }
}

这个示例将一个自定义的QQuickFramebufferObject元素添加到界面中，然后在这个元素中创建一个Pbuffer表面，并将其和OpenGL ES上下文绑定。在渲染时，将Pbuffer表面渲染到QOpenGLFramebufferObject对象中，并通过QQuickFramebufferObject元素显示出来。