OpenGL 实现多通道

Question

我在将我在 Shadertoy 中成功实现的一些代码移植到桌面 OpenGL 时遇到问题，问题是我需要创建一个 FrameBufferObject FBO，以便我可以进行屏幕外计算，稍后将传递对于主要的 glsl 片段着色器，问题是这个缓冲区需要将自身作为纹理引用以获取之前的值，以便能够运行模拟。

我已经成功创建了FBO：

// Framebuffer configuration.
unsigned int frameBufferOne;
glGenFramebuffers(1, &frameBufferOne);
glBindFramebuffer(GL_FRAMEBUFFER, frameBufferOne);

// Create a colour attachment texture.
unsigned int textureColourBufferOne;
glGenTextures(1, &textureColourBufferOne);
glBindTexture(GL_TEXTURE_2D, textureColourBufferOne);
glTexImage2D(GL_TEXTURE_2D, 0, GL_RGB, WIDTH, HEIGHT, 0, GL_RGB, 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, textureColourBufferOne, 0);

if (glCheckFramebufferStatus(GL_FRAMEBUFFER) != GL_FRAMEBUFFER_COMPLETE)
    std::cout << "ERROR::FRAMEBUFFER:: Framebuffer is not complete!" << std::endl;
glBindFramebuffer(GL_FRAMEBUFFER, 0);

并设法在我的渲染循环中调用它，以便我可以渲染到 FBO，然后将这些值传递到默认帧缓冲区：

// Render Loop.
while( !glfwWindowShouldClose( window ) )
{

    // Input.
    processInput( window );

    // Render.

    // Bind to frameBuffer and draw scene as normally would to colour texture.
    glBindFramebuffer( GL_FRAMEBUFFER, frameBufferOne );

    glClearColor( 0.2f, 0.3f, 0.1f, 1.0f );
    glClear( GL_COLOR_BUFFER_BIT );

    bufferShader.use();
    float currentFrame = glfwGetTime();
    //Set the iTimeDelta uniform.
    float deltaTime = currentFrame - lastFrame;
    lastFrame = currentFrame;
    bufferShader.setFloat( "iTimeDelta", deltaTime );
    // Set the iTime uniform.
    float timeValue = currentFrame;
    bufferShader.setFloat( "iTime", timeValue );
    // Set the iResolution uniform.
    bufferShader.setVec2( "iResolution", WIDTH, HEIGHT );
    // Input iMouse.
    double xPos, yPos;
    glfwGetCursorPos( window, &xPos, &yPos );
    yPos = HEIGHT - yPos;
    bufferShader.setVec2( "iMouse", xPos, yPos );

    glBindVertexArray( VAO );
    glBindTexture( GL_TEXTURE_2D, textureColourBufferOne );
    glDrawElements( GL_TRIANGLES, 6, GL_UNSIGNED_INT, 0 );
    glBindVertexArray( 0 );

    glBindFramebuffer( GL_FRAMEBUFFER, 0 );
    glDisable( GL_DEPTH_TEST );

    glClearColor( 1.0f, 1.0f, 1.0f, 1.0f );
    glClear( GL_COLOR_BUFFER_BIT );

    ourShader.use();
    ourShader.setVec2( "iResolution", WIDTH, HEIGHT );
    // Set the iTime uniform.
    ourShader.setFloat( "iTime", timeValue );
    glBindVertexArray(VAO);
    glBindTexture( GL_TEXTURE_2D, textureColourBufferOne );
    glDrawElements( GL_TRIANGLES, 6, GL_UNSIGNED_INT, 0 );

    glfwSwapBuffers( window );
    glfwPollEvents();

    frameCount++;
    finalTime = time( NULL );
    if( finalTime - initialTime > 0 )
    {

        std::cout << "FPS : " << frameCount / (finalTime - initialTime) << std::endl;
        frameCount = 0;
        initialTime = finalTime;

    }

但我无法将缓冲区作为纹理渲染到自身，我知道它会输出未定义的行为，我应该使用 Ping-Pong 技术。

有人能指出我正确的方向吗？

Answer 1

But I am not able to render the buffer to itself as a texture, I understand that it outputs undefined behaviour and that I should be using a technique as Ping-Pong.

Can somebody point me in the right direction?

您必须创建 2 个帧缓冲区对象，就像您在问题中所做的那样：frameBufferOne 和 frameBufferTwo.
这 2 个帧缓冲区对象中的每一个都必须附加一个纹理对象：textureColourBufferOne 和 textureColourBufferTwo.

在程序的主循环中，您必须知道帧数是偶数还是奇数。
如果数字是偶数，那么你必须渲染到 textureColourBufferOne 并且渲染通道的输入是 textureColourBufferTwo.
如果数字是奇数，那么您必须渲染到 textureColourBufferTwo 并且渲染过程的输入是 textureColourBufferOne.
渲染的结果总是存储在属于当前帧的帧缓冲区的纹理中：

bool even = true;
while( !glfwWindowShouldClose( window ) )
{
    .....

    glBindFramebuffer( GL_FRAMEBUFFER, even ? frameBufferOne : frameBufferTwo );

    glClearColor( 0.2f, 0.3f, 0.1f, 1.0f );
    glClear( GL_COLOR_BUFFER_BIT );

    .....

    glBindVertexArray( VAO );
    glBindTexture( GL_TEXTURE_2D, even ? textureColourBufferTwo : textureColourBufferOne );
    glDrawElements( GL_TRIANGLES, 6, GL_UNSIGNED_INT, 0 );
    glBindVertexArray( 0 );

    .....

    glBindFramebuffer( GL_FRAMEBUFFER, 0 );
    glClearColor( 1.0f, 1.0f, 1.0f, 1.0f );
    glClear( GL_COLOR_BUFFER_BIT );

    .....

    glBindVertexArray(VAO);
    glBindTexture( GL_TEXTURE_2D, even ? textureColourBufferOne : textureColourBufferTwo );
    glDrawElements( GL_TRIANGLES, 6, GL_UNSIGNED_INT, 0 );

    glfwSwapBuffers( window );
    glfwPollEvents();

    even = !even;

    .....
}

OpenGL 实现多通道

OpenGL Implementing MultiPass

c++

opengl

shader

glsl

fragment-shader