OpenGL FBO 混合/Blitting 问题

Question

TL;DR：当缩小混合实体时，边缘呈锯齿状，但在放大时呈现完美。 发生在我的文字和圈子中。

我有一个图形引擎，可以渲染到一个多采样 FBO 并将它的 blits 到另一个非多采样纹理附件。

每当我渲染文本并充分放大它时，它都会完美呈现。 当我缩小边缘开始变得锯齿状时。 似乎也可以看到纹理的边缘。 请参阅附图以供参考。

放大时正确呈现文本：

缩小时带有锯齿状边缘的文本：

我认为这与混合有关。 我通过绘制一个四边形然后将其着色为一个圆圈来渲染我的圆圈，并且在这些边缘上也会发生同样的事情。

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GLCall()是一个 function，它允许我检查每个 OpenGL function 上的错误。 它可以是 ingored。

OpenGL 设置

这是在任何渲染发生之前调用的。

    // OpenGL settings.
    GLCall(glEnable(GL_MULTISAMPLE));                               // Enables MSAA.
    GLCall(glEnable(GL_DEPTH_TEST));                                // Enables depth testing for the OpenGL scenes.
    GLCall(glDepthFunc(GL_LESS));                                   // Set the function used with depth testing.
    GLCall(glEnable(GL_BLEND));                                     // Enable blending for alpha channels.
    GLCall(glBlendFunc(GL_SRC_ALPHA, GL_ONE_MINUS_SRC_ALPHA));      // Set blend function.  This is the standard setting.
    GLCall(glClearColor(0.17f, 0.17f, 0.17f, 1.0f));                // Set the color to which OpenGL clears.

FBO创建

    // Generate MSAA FBO.
    GLCall(glGenFramebuffers(1, &m_msaaFrameBufferID));
    GLCall(glGenTextures(1, &m_msaaColorTextureID));
    GLCall(glGenTextures(1, &m_msaaEntityIDTextureID));
    GLCall(glGenRenderbuffers(1, &m_msaaDepthStencilBufferID));
    // Check for generation error.
    if (!glCheckFramebufferStatus(GL_FRAMEBUFFER))
    { std::cout << red << "\n\n[OPENGL] [ERROR] :" << white << " MSAA FBO could not be generated.\n"; }

    // Generate render FBO.
    GLCall(glGenFramebuffers(1, &m_renderFrameBufferID));
    GLCall(glGenTextures(1, &m_renderColorTextureID));
    GLCall(glGenTextures(1, &m_renderEntityIDTextureID));
    // Check for generation error.
    if (!glCheckFramebufferStatus(GL_FRAMEBUFFER))
    { std::cout << red << "\n\n[OPENGL] [ERROR] :" << white << " Render FBO could not be generated.\n"; }

    // -------------------------------- //
    //  M S A A   A T T A C H M E N T S //
    // -------------------------------- //

    // Bind MSA FBO.
    GLCall(glBindFramebuffer(GL_FRAMEBUFFER, m_msaaFrameBufferID));
    // Generate and attach MSAA color texture.
    GLCall(glBindTexture(GL_TEXTURE_2D_MULTISAMPLE, m_msaaColorTextureID));
    GLCall(glTexImage2DMultisample(GL_TEXTURE_2D_MULTISAMPLE, m_MSAA, GL_RGBA, width, height, GL_TRUE));
    GLCall(glFramebufferTexture2D(GL_FRAMEBUFFER, GL_COLOR_ATTACHMENT0, GL_TEXTURE_2D_MULTISAMPLE, m_msaaColorTextureID, 0));
    // Generate and attach MSAA entityID buffer.
    GLCall(glBindTexture(GL_TEXTURE_2D_MULTISAMPLE, m_msaaEntityIDTextureID));
    GLCall(glTexImage2DMultisample(GL_TEXTURE_2D_MULTISAMPLE, m_MSAA, GL_R32UI, width, height, GL_TRUE));
    GLCall(glFramebufferTexture2D(GL_FRAMEBUFFER, GL_COLOR_ATTACHMENT1, GL_TEXTURE_2D_MULTISAMPLE, m_msaaEntityIDTextureID, 0));
    // Enable draw buffers.
    GLenum drawBuffers[2] = {GL_COLOR_ATTACHMENT0, GL_COLOR_ATTACHMENT1};
    GLCall(glDrawBuffers(2, drawBuffers));
    // Create depth/stencil MSAA buffer texture.
    GLCall(glBindRenderbuffer(GL_RENDERBUFFER, m_msaaDepthStencilBufferID));
    GLCall(glRenderbufferStorageMultisample(GL_RENDERBUFFER, m_MSAA, GL_DEPTH24_STENCIL8, width, height));
    GLCall(glFramebufferRenderbuffer(GL_FRAMEBUFFER, GL_DEPTH_STENCIL_ATTACHMENT, GL_RENDERBUFFER, m_msaaDepthStencilBufferID));    
    // Check for completion errror.
    if (glCheckFramebufferStatus(GL_FRAMEBUFFER) != GL_FRAMEBUFFER_COMPLETE)
        std::cout << red << "\n\n[OPENGL] [ERROR] :" << white << " MSAA FBO is not complete.\n" << std::endl;

    // ------------------------------------- //
    //  R E N D E R   A T T A C H M E N T S  //
    // ------------------------------------- //

    // Bind render FBO.
    GLCall(glBindFramebuffer(GL_FRAMEBUFFER, m_renderFrameBufferID));
    // Generate and attach color texture.
    GLCall(glBindTexture(GL_TEXTURE_2D, m_renderColorTextureID));
    GLCall(glTexImage2D(GL_TEXTURE_2D, 0, GL_RGB, width, height, 0, GL_RGB, GL_UNSIGNED_BYTE, NULL));
    GLCall(glTexParameteri(GL_TEXTURE_2D, GL_TEXTURE_MIN_FILTER, GL_LINEAR));
    GLCall(glTexParameteri(GL_TEXTURE_2D, GL_TEXTURE_MAG_FILTER, GL_LINEAR));
    GLCall(glTexParameteri(GL_TEXTURE_2D, GL_TEXTURE_WRAP_R, GL_CLAMP_TO_EDGE));
    GLCall(glTexParameteri(GL_TEXTURE_2D, GL_TEXTURE_WRAP_S, GL_CLAMP_TO_EDGE));
    GLCall(glTexParameteri(GL_TEXTURE_2D, GL_TEXTURE_WRAP_T, GL_CLAMP_TO_EDGE));
    GLCall(glFramebufferTexture2D(GL_FRAMEBUFFER, GL_COLOR_ATTACHMENT0, GL_TEXTURE_2D, m_renderColorTextureID, 0));
    // Generate Entity ID texture.
    GLCall(glBindTexture(GL_TEXTURE_2D, m_renderEntityIDTextureID));
    GLCall(glTexImage2D(GL_TEXTURE_2D, 0, GL_R32UI, width, height, 0, GL_RED_INTEGER, GL_UNSIGNED_BYTE, NULL));
    GLCall(glTexParameteri(GL_TEXTURE_2D, GL_TEXTURE_MIN_FILTER, GL_LINEAR));
    GLCall(glTexParameteri(GL_TEXTURE_2D, GL_TEXTURE_MAG_FILTER, GL_LINEAR));
    GLCall(glTexParameteri(GL_TEXTURE_2D, GL_TEXTURE_WRAP_R, GL_CLAMP_TO_EDGE));
    GLCall(glTexParameteri(GL_TEXTURE_2D, GL_TEXTURE_WRAP_S, GL_CLAMP_TO_EDGE));
    GLCall(glTexParameteri(GL_TEXTURE_2D, GL_TEXTURE_WRAP_T, GL_CLAMP_TO_EDGE));
    GLCall(glFramebufferTexture2D(GL_FRAMEBUFFER, GL_COLOR_ATTACHMENT1, GL_TEXTURE_2D, m_renderEntityIDTextureID, 0));
    // Check for completion errror.
    if (glCheckFramebufferStatus(GL_FRAMEBUFFER) != GL_FRAMEBUFFER_COMPLETE)
        std::cout << red << "\n\n[OPENGL] [ERROR] :" << white << " Render FBO is not complete.\n" << std::endl;

    // --------------- //
    //  C L E A N U P  //
    // --------------- //

    // Unbind.
    GLCall(glBindFramebuffer(GL_FRAMEBUFFER, 0));

FBO 位图

    // Resolve the MSAA and copy to the render FBO.
    GLCall(glBindFramebuffer(GL_READ_FRAMEBUFFER, m_msaaFrameBufferID));
    GLCall(glBindFramebuffer(GL_DRAW_FRAMEBUFFER, m_renderFrameBufferID));
    GLCall(glReadBuffer(GL_COLOR_ATTACHMENT0));
    GLCall(glDrawBuffer(GL_COLOR_ATTACHMENT0));
    GLCall(glBlitFramebuffer(0, 0, m_viewport[0], m_viewport[1], 0, 0, m_viewport[0], m_viewport[1], GL_COLOR_BUFFER_BIT, GL_LINEAR));
    GLCall(glBindFramebuffer(GL_FRAMEBUFFER, 0));
    return m_renderColorTextureID;

渲染循环

    // ----------- //
    //  S E T U P  //
    // ----------- //

    // Enable blending.
    GLCall(glEnable(GL_BLEND));
    // Set glViewport for the ImGUI context.
    GLCall(glViewport(0, 0, (GLsizei)m_imGuiViewportDimensions[0], 
                            (GLsizei)m_imGuiViewportDimensions[1]));
    // Calculate and update the engine matrices.
    m_viewMatrix = m_scalingMatrix * m_rotationMatrix * m_translationMatrix;
    // Render to frame buffer.
    m_frameBuffer->bind();
    m_frameBuffer->clear();

    // ------------------- //
    //  R E N D E R I N G  //
    // ------------------- //

    // Render here.

    // --------------- //
    //  C L E A N U P  //
    // --------------- //
     
    // Stop rendering to the current FBO.
    m_frameBuffer->unbind();
    // Disable blending.
    GLCall(glDisable(GL_BLEND));

FBO 清除

    GLCall(glClear(GL_DEPTH_BUFFER_BIT));                                   // Clear depth buffer.
    GLCall(glClearTexImage(m_msaaColorTextureID, 0, GL_RGBA, GL_FLOAT, 0)); // Clear color attachment.