C++ 使用OpengGLES2（角度）从帧缓冲区对象读取

使用Angle编程UWP应用程序以运行OpenGL ES，我面临一个问题，即使用

glReadPixels

从帧缓冲区对象读取的基本操作。 从VisualStudio模板“OpenglES2应用程序（Android、iOS、Windows Universal）”开始，我可以将默认场景渲染检索到内存缓冲区中

初始化：

void SimpleRenderer::InitFbo()
{
    int buf_size = tex_height*tex_width * 4;
    mReadBuf = new char[buf_size];
    memset(mReadBuf, 123, buf_size); // arbitrary value to detect changes
}

void SimpleRenderer::InitFbo()
{
    glGenFramebuffers(1, &mRenderFbo);
    glGenTextures(1, &mRenderTexture);
    int buf_size = tex_height*tex_width * 4;
    char*buf = new char[buf_size];
    memset(buf, 255, buf_size);

    glBindTexture(GL_TEXTURE_2D, mRenderTexture);
    glTexImage2D(GL_TEXTURE_2D, 0, 4,
            tex_width,
            tex_height,
            0, GL_RGBA, GL_UNSIGNED_BYTE,
            buf);

    glBindFramebuffer(GL_FRAMEBUFFER, mRenderFbo);
    glFramebufferTexture2D(GL_FRAMEBUFFER, GL_COLOR_ATTACHMENT0, GL_TEXTURE_2D,
            mRenderTexture, 0);

    glBindFramebuffer(GL_FRAMEBUFFER, 0);
    delete[] buf;

    mReadBuf = new char[buf_size];
    memset(mReadBuf, 123, buf_size);
}

绘图功能：

void SimpleRenderer::Draw()
{

    // drawing calls here
    // (...)

    glReadPixels(0, 0, tex_width, tex_height, GL_RGBA, GL_UNSIGNED_BYTE, mReadBuf);
    // success : mReadBuf is updated with pixel values
}

void SimpleRenderer::Draw()
{
    glBindFramebuffer(GL_FRAMEBUFFER, mRenderFbo);

    // drawing calls here
    // (...)

    glReadPixels(0, 0, tex_width, tex_height, GL_RGBA, GL_UNSIGNED_BYTE, mReadBuf);

    // failure : mReadBuf is unchanged

    glBindFramebuffer(GL_FRAMEBUFFER, 0);
}

但是如果我只是创建一个帧缓冲区对象，尝试在那里绘制并检索结果，

glReadPixels

不返回任何值，

glError

返回

无效的\u帧缓冲区\u操作

初始化：

void SimpleRenderer::InitFbo()
{
    int buf_size = tex_height*tex_width * 4;
    mReadBuf = new char[buf_size];
    memset(mReadBuf, 123, buf_size); // arbitrary value to detect changes
}

void SimpleRenderer::InitFbo()
{
    glGenFramebuffers(1, &mRenderFbo);
    glGenTextures(1, &mRenderTexture);
    int buf_size = tex_height*tex_width * 4;
    char*buf = new char[buf_size];
    memset(buf, 255, buf_size);

    glBindTexture(GL_TEXTURE_2D, mRenderTexture);
    glTexImage2D(GL_TEXTURE_2D, 0, 4,
            tex_width,
            tex_height,
            0, GL_RGBA, GL_UNSIGNED_BYTE,
            buf);

    glBindFramebuffer(GL_FRAMEBUFFER, mRenderFbo);
    glFramebufferTexture2D(GL_FRAMEBUFFER, GL_COLOR_ATTACHMENT0, GL_TEXTURE_2D,
            mRenderTexture, 0);

    glBindFramebuffer(GL_FRAMEBUFFER, 0);
    delete[] buf;

    mReadBuf = new char[buf_size];
    memset(mReadBuf, 123, buf_size);
}

绘图功能：

void SimpleRenderer::Draw()
{

    // drawing calls here
    // (...)

    glReadPixels(0, 0, tex_width, tex_height, GL_RGBA, GL_UNSIGNED_BYTE, mReadBuf);
    // success : mReadBuf is updated with pixel values
}

void SimpleRenderer::Draw()
{
    glBindFramebuffer(GL_FRAMEBUFFER, mRenderFbo);

    // drawing calls here
    // (...)

    glReadPixels(0, 0, tex_width, tex_height, GL_RGBA, GL_UNSIGNED_BYTE, mReadBuf);

    // failure : mReadBuf is unchanged

    glBindFramebuffer(GL_FRAMEBUFFER, 0);
}

*编辑-由于下面的评论而解决。需要正确初始化纹理

glTexImage2D(GL_TEXTURE_2D, 0, GL_RGBA,
    tex_width,
    tex_height,
    0, GL_RGBA, GL_UNSIGNED_BYTE,
    buf);

---

对于记录，在它得到解决之前，我正在使用

glCheckFramebufferStatus

检查帧缓冲区状态，它返回

GL\u framebuffer\u complete\u ATTACHMENT

OpenGL函数的第三个参数指定纹理缓冲区的内部格式

在方法

SimpleRenderer:：InitFbo

中，将

4

传递给内部格式，该格式不是有效的参数。改用

GL\u RGBA

：

glTexImage2D(GL_TEXTURE_2D, 0, 
        GL_RGBA,   // <-----------------------
        tex_width,
        tex_height,
        0, GL_RGBA, GL_UNSIGNED_BYTE,
        buf);

glTexImage2D（GL_纹理_2D，0，
GL_RGBA，//完成；对不起，我到处找，但找不到验证答案的方法。谢谢你的帮助。