OpenGL渲染到多个纹理，结果是白色的

Posted 2023-02-22

【中文标题】OpenGL渲染到多个纹理，结果是白色的

【英文标题】：OpenGL Rendering to Multiple Textures, results are white

【发布时间】：2012-05-16 19:51:30

【问题描述】：

我已经开始切换我的渲染代码以支持着色器，并且在渲染到后台缓冲区时一切正常。所以现在我正在努力渲染到 FBO，但我得到的只是颜色和法线的白色纹理。

这是我的 FBO 创建代码：

void RenderTarget_GL::CreateFBO (void)

  // if the machine supports the GL FBO extension
  if (s_supportfbo)
  
    // Create FBO
    glGenFramebuffersEXT(1, &m_fbo);
    glBindFramebufferEXT(GL_FRAMEBUFFER_EXT, m_fbo);

    // Create default texture buffer
    char *buffer = new char [static_cast<int>(g_window->GetWidth() * m_screenWidth) * static_cast<int>(g_window->GetHeight() * m_screenHeight) * 4];
    std::memset(buffer, 0, static_cast<int>(g_window->GetWidth() * m_screenWidth) * static_cast<int>(g_window->GetHeight() * m_screenHeight) * 4);

    // Create Render Texture
    glGenTextures(1, &m_rendertexture);
    glBindTexture(GL_TEXTURE_2D, m_rendertexture);
    glTexImage2D(GL_TEXTURE_2D, 0, 4, static_cast<int>(g_window->GetWidth() * m_screenWidth), static_cast<int>(g_window->GetHeight() * m_screenHeight), 0, GL_RGBA, GL_UNSIGNED_BYTE, buffer);

    // Bind Render Texture to FBO
    glBindTexture(GL_TEXTURE_2D, 0);
    glFramebufferTexture2DEXT(GL_FRAMEBUFFER_EXT, GL_COLOR_ATTACHMENT0_EXT, GL_TEXTURE_2D, m_rendertexture, 0);

    // Create Normal Texture if this FBO will be rendering normals
    if (m_hasnormal)
    
      glGenTextures(1, &m_normaltexture);
      glTexImage2D(GL_TEXTURE_2D, 0, 4, static_cast<int>(g_window->GetWidth() * m_screenWidth), static_cast<int>(g_window->GetHeight() * m_screenHeight), 0, GL_RGBA, GL_UNSIGNED_BYTE, buffer);

      // Bind Normal Texture to FBO
      glFramebufferTexture2DEXT(GL_FRAMEBUFFER_EXT, GL_COLOR_ATTACHMENT1_EXT, GL_TEXTURE_2D, m_normaltexture, 0);
    

    // UnBind FBO and cleanup default buffer
    delete [] buffer;
    Clear();
  

以及我用来设置当前渲染目标的代码：

void RenderTarget_GL::Set (void)

  if (s_supportfbo && g_glgraphics->GetShaderEnabled())
  
    static const GLenum buffer1[] = GL_COLOR_ATTACHMENT0_EXT;
    static const GLenum buffer2[] = GL_COLOR_ATTACHMENT0_EXT, GL_COLOR_ATTACHMENT1_EXT;

    glBindFramebufferEXT(GL_FRAMEBUFFER_EXT, m_fbo);
    if (m_hasnormal)
      glDrawBuffers(2, buffer2);
    else
      glDrawBuffers(1, buffer1);
  

最后，我的实际绘图代码：

glClear(GL_COLOR_BUFFER_BIT | GL_DEPTH_BUFFER_BIT | GL_STENCIL_BUFFER_BIT);
// Setup the camera transformation
glMatrixMode(GL_MODELVIEW);
glPushMatrix();

if (m_camera)
  m_camera->GLMatrix();
else
  m_defaultCam.GLMatrix();

// Setup Render Target
if (m_shaderenabled)

  glPushAttrib(GL_VIEWPORT_BIT);
  glViewport(0,0,g_window->GetWidth(),g_window->GetHeight());
  m_initialpass->Set();


// Draw All Objects with their per-object shaders

// Clear render target and shader bindings
if (m_shaderenabled)

  glPopAttrib();
  RenderTarget_GL::Clear();
  Shader_GL::ClearShaderBinding();


glPopMatrix();

glMatrixMode(GL_PROJECTION);
glPushMatrix();
glLoadIdentity();

// Draw Scene
glActiveTexture(GL_TEXTURE0);
glBindTexture(GL_TEXTURE_2D, m_initialpass->GetColorTexture());
glBegin(GL_QUADS);
  glTexCoord2f(0.0f, 0.0f);
  glVertex3f(-1.0f, -1.0f, 0.0f);
  glTexCoord2f(1.0f, 0.0f);
  glVertex3f(1.0f, -1.0f, 0.0f);
  glTexCoord2f(1.0f, 1.0f);
  glVertex3f(1.0f, 1.0f, 0.0f);
  glTexCoord2f(0.0f, 1.0f);
  glVertex3f(-1.0f, 1.0f, 0.0f);
glEnd();

Texture_GL::ClearTextureBinding();
glPopMatrix();

// Swap Buffers

【参考方案1】：

GL_TEXTURE_MIN_FILTER 默认为GL_NEAREST_MIPMAP_LINEAR。提供 mipmap 或切换到 GL_LINEAR 或 GL_NEAREST。

OpenGL Wiki has more.

【讨论】：

谢谢，忘记了 mipmapping 并且认为这不会有问题。也错过了对 FBO 的 glClear 的调用，我的纹理颠倒了，但这些都是微不足道的修复

是的，这个问题似乎吸引了很多人。因此 Wiki 上的常见问题解答 :)