使用QOpenGLTexture和QOpenGLFramebufferObject渲染到和WITH纹理

本文介绍了使用QOpenGLTexture和QOpenGLFramebufferObject渲染到和WITH纹理的处理方法，对大家解决问题具有一定的参考价值，需要的朋友们下面随着小编来一起学习吧！

问题描述

根据Qt5中的QOpenGLTexture文档，可以渲染 WITH 纹理，也可以渲染 TO 纹理.关于这两种用法，是否有任何简单的示例?可以在.下面列出了与此有关的有问题的代码:

According to the document of QOpenGLTexture in Qt5, one can render WITH texture, and can also render TO texture. Is there any simple example about these two usages?The scenario of such usages could be found at this link. The problematic codes about this are listed below:

屏幕外渲染的初始化:

p_offscreen_context_ = std::make_unique<QOpenGLContext>();
p_offscreen_context_->setFormat(_p_onscreen_context->format()); // _p_onscreen_context is the context in the onscreen rendering part
p_offscreen_context_->setShareContext(_p_onscreen_context);
if (!p_offscreen_context_->create()) {
    std::cerr << "Failed to create OpenGL context!!" << std::endl;
    return;
}
p_offscreen_surface_ = std::make_unique<QOffscreenSurface>();
p_offscreen_surface_->setFormat(p_offscreen_context_->format());
p_offscreen_surface_->create();
if (!p_offscreen_surface_->isValid()) {
    std::cerr << "Failed to create Offscreen Surface!!" << std::endl;
    return;
}
make_current(); // p_offscreen_context_->makeCurrent(p_offscreen_surface_.get());
p_functions_ = std::make_unique<QOpenGLFunctions>();
p_functions_->initializeOpenGLFunctions();
create_frame_buffer_object(); // see below
done_current(); // p_offscreen_context_->doneCurrent();

在功能create_frame_buffer_object()中:

make_current();
if (p_frame_buffer_object_) { p_frame_buffer_object_->release(); }
QOpenGLFramebufferObjectFormat format;
format.setSamples(0);
p_frame_buffer_object_ =
    std::make_shared<QOpenGLFramebufferObject>(width_, height_, format); // width_ and height_ represent the size of buffer
if (!p_frame_buffer_object_->isValid()) {
  std::cerr << "Failed to create Frame Buffer Object!!" << std::endl;
  return;
}
p_frame_buffer_object_->bind();
p_functions_->glClear(
    GL_COLOR_BUFFER_BIT | GL_DEPTH_BUFFER_BIT | GL_STENCIL_BUFFER_BIT);
p_frame_buffer_object_->release();
done_current();

进行渲染:

std::lock_guard<std::mutex> lock_guard(mutex_);
make_current();
if (!initialized_.exchange(true)) { initiate_opengl(); } // do some initilization in the renderer part, see below
p_frame_buffer_object_->bind();
paint_opengl(); // do the rendering in the renderer part
texture_unit_ = p_frame_buffer_object_->texture(); // record the texture unit used in the FBO
p_frame_buffer_object_->release();
done_current();

屏幕上的部分:

这部分仅涉及渲染器的初始化和渲染.没什么.

The onscreen part:

This part simply involves the initialization and rendering of the renderer. Nothing else.

初始化:

// creations of vertex array object, vertex index buffer and other resources are omitted

// creation of the QOpenGLTexture (might be wrong, but don't know how to fix)
p_texture_ = std::make_shared<QOpenGLTexture>(image.mirrored()); // image is a QImage which has the same width and height as FBO

进行渲染:

// Render image via shader
p_program_->bind(); // shaders have been successfully compiled
{
    p_vertex_array_object_->bind();
    bind_texture(); // for offscreen part: p_texture_->bind();
                    // for onscreen part: p_texture_->bind(unit_);
                    // unit_ is the value of texture_unit_ from offscreen part
    ::glDrawElements(GL_TRIANGLE_FAN,
                     static_cast<GLsizei>(vertex_indices_.size()),
                     GL_UNSIGNED_SHORT,
                     static_cast<void *>(0)); // actually draw a quad 
    release_texture(); // for offscreen part: p_texture_->release();
                       // for onscreen part: p_texture_->release(unit_);
    p_vertex_array_object_->release();
}
p_program_->release();

我对QOpenGLTexture和QOpenGLFramebufferObject的机制不太熟悉，因此任何修复我的错误并向我展示该机制的人都将不胜感激.

I do not quite familiar with the mechanism of QOpenGLTexture and QOpenGLFramebufferObject, so anyone fixing my error and showing me the mechanism will be much appreciated.

渲染