Question

我想使用“渲染纹理”范例来编写OpenGL 3D渲染的.png屏幕截图。我可以在没有的情况下进行多次采样，但是我一直在努力获取抗锯齿图像。

首先，这可能吗？

第二，API调用的正确组合是什么？

（第三个问题，我该如何更好地调试它？glCheckFramebufferStatus显然还不够）。

这就是我正在使用的东西：

  // https://stackoverflow.com/questions/7402504/multisampled-render-to-texture-in-ios
  GLuint texture;
  glGenTextures(1, &texture);
  glBindTexture(GL_TEXTURE_2D, texture);
  glTexImage2D(GL_TEXTURE_2D, 0, GL_RGBA4, width, height, 0, GL_RGBA, GL_UNSIGNED_BYTE, NULL);

  GLuint resolved_framebuffer, resolvedColorRenderbuffer;
  glGenFramebuffers(1, &resolved_framebuffer);
  glBindFramebuffer(GL_FRAMEBUFFER, resolved_framebuffer);
  glGenRenderbuffers(1, &resolvedColorRenderbuffer);
  glBindRenderbuffer(GL_RENDERBUFFER, resolvedColorRenderbuffer);
  glFramebufferTexture2D(GL_FRAMEBUFFER, GL_COLOR_ATTACHMENT0, GL_TEXTURE_2D, texture, 0);

  assert(glCheckFramebufferStatus(GL_FRAMEBUFFER) == GL_FRAMEBUFFER_COMPLETE);

  GLuint framebuffer;
  glGenFramebuffers(1, &framebuffer);
  glBindFramebuffer(GL_FRAMEBUFFER, framebuffer);

  GLuint colorRenderbuffer, depthRenderbuffer;
  glGenRenderbuffers(1, &colorRenderbuffer);
  glBindRenderbuffer(GL_RENDERBUFFER, colorRenderbuffer);
  glRenderbufferStorageMultisample(GL_RENDERBUFFER, 4, GL_RGBA8, width, height);
  glFramebufferRenderbuffer(GL_FRAMEBUFFER, GL_COLOR_ATTACHMENT0, GL_RENDERBUFFER, colorRenderbuffer);

  glGenRenderbuffers(1, &depthRenderbuffer);
  glBindRenderbuffer(GL_RENDERBUFFER, depthRenderbuffer);
  glRenderbufferStorageMultisample(GL_RENDERBUFFER, 4, GL_DEPTH_COMPONENT16, width, height);
  glFramebufferRenderbuffer(GL_FRAMEBUFFER, GL_DEPTH_ATTACHMENT, GL_RENDERBUFFER, depthRenderbuffer);


  assert(glCheckFramebufferStatus(GL_FRAMEBUFFER) == GL_FRAMEBUFFER_COMPLETE);

  glBindFramebuffer( GL_FRAMEBUFFER, framebuffer );
  glClearColor(background_color(0), background_color(1), background_color(2), 0.f);
  glClear(GL_COLOR_BUFFER_BIT);// | GL_DEPTH_BUFFER_BIT);

  draw_scene();

  glBindFramebuffer( GL_READ_FRAMEBUFFER, framebuffer );
  glBindFramebuffer( GL_DRAW_FRAMEBUFFER, resolved_framebuffer );
  // https://forum.juce.com/t/ios-8-getting-the-demo-building/13570/20
  glBlitFramebuffer(0, 0, width, height, 0, 0, width, height, GL_COLOR_BUFFER_BIT, GL_NEAREST);
  // ^--- this is throwing `GL_INVALID_OPERATION`


  GLubyte* pixels = (GLubyte*)calloc(width*height*4,sizeof(GLubyte));
  glReadPixels(0, 0,width, height,GL_RGBA, GL_UNSIGNED_BYTE, pixels);

  writePNG(pixels);

当前，我得到一张空白图像，glBlitFramebuffer抛出GL_INVALID_OPERATION。显然是this error can correspond to many things，但我不确定哪个适用。根据{{1}}，我的缓冲区看起来“不错”。

此问题之前曾以类似的形式被提出：

但是，所有答案都没有一个完整的可行示例。我很想找到/创建一个 minimum 示例。

Answer 1

https://learnopengl.com/Advanced-OpenGL/Anti-Aliasing上的教程基本上满足了我的需求。可行的解决方案是：

  unsigned int framebuffer;
  glGenFramebuffers(1, &framebuffer);
  glBindFramebuffer(GL_FRAMEBUFFER, framebuffer);
  // create a multisampled color attachment texture
  unsigned int textureColorBufferMultiSampled;
  glGenTextures(1, &textureColorBufferMultiSampled);
  glBindTexture(GL_TEXTURE_2D_MULTISAMPLE, textureColorBufferMultiSampled);
  glTexImage2DMultisample(GL_TEXTURE_2D_MULTISAMPLE, 4, GL_RGBA, width, height, GL_TRUE);
  glBindTexture(GL_TEXTURE_2D_MULTISAMPLE, 0);
  glFramebufferTexture2D(GL_FRAMEBUFFER, GL_COLOR_ATTACHMENT0, GL_TEXTURE_2D_MULTISAMPLE, textureColorBufferMultiSampled, 0);
  // create a (also multisampled) renderbuffer object for depth and stencil attachments
  unsigned int rbo;
  glGenRenderbuffers(1, &rbo);
  glBindRenderbuffer(GL_RENDERBUFFER, rbo);
  glRenderbufferStorageMultisample(GL_RENDERBUFFER, 4, GL_DEPTH24_STENCIL8, width, height);
  glBindRenderbuffer(GL_RENDERBUFFER, 0);
  glFramebufferRenderbuffer(GL_FRAMEBUFFER, GL_DEPTH_STENCIL_ATTACHMENT, GL_RENDERBUFFER, rbo);
  assert(glCheckFramebufferStatus(GL_FRAMEBUFFER) == GL_FRAMEBUFFER_COMPLETE);
  glBindFramebuffer(GL_FRAMEBUFFER, 0);

  // configure second post-processing framebuffer
  unsigned int intermediateFBO;
  glGenFramebuffers(1, &intermediateFBO);
  glBindFramebuffer(GL_FRAMEBUFFER, intermediateFBO);
  // create a color attachment texture
  unsigned int screenTexture;
  glGenTextures(1, &screenTexture);
  glBindTexture(GL_TEXTURE_2D, screenTexture);
  glTexImage2D(GL_TEXTURE_2D, 0, GL_RGBA, width, height, 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);
  glFramebufferTexture2D(GL_FRAMEBUFFER, GL_COLOR_ATTACHMENT0, GL_TEXTURE_2D, screenTexture, 0);    // we only need a color buffer
  assert(glCheckFramebufferStatus(GL_FRAMEBUFFER) == GL_FRAMEBUFFER_COMPLETE);
  glBindFramebuffer(GL_FRAMEBUFFER, 0);

  glBindFramebuffer(GL_FRAMEBUFFER, framebuffer);

  draw_scene();

  glBindFramebuffer(GL_READ_FRAMEBUFFER, framebuffer);
  glBindFramebuffer(GL_DRAW_FRAMEBUFFER, intermediateFBO);
  glBlitFramebuffer(0, 0, width, height, 0, 0, width, height, GL_COLOR_BUFFER_BIT, GL_NEAREST);

  glBindFramebuffer(GL_FRAMEBUFFER, intermediateFBO);
  GLubyte* pixels = (GLubyte*)calloc(width*height*4,sizeof(GLubyte));
  glReadPixels(0, 0,width, height,GL_RGBA, GL_UNSIGNED_BYTE, pixels);

  writePNG(pixels);

似乎原始问题中的代码中至少存在两个错误：

framebuffer应该附加多样本纹理，而不是渲染缓冲区（glFramebufferTexture2D(... GL_TEXTURE_2D_MULTISAMPLE而不是glRenderbufferStorageMultisample）
发短信之后glBindFramebuffer(GL_FRAMEBUFFER, intermediateFBO);之前必须致电glReadPixels

如何将抗锯齿图像渲染为纹理（然后写入PNG）？

1 个答案: