c++ - OpenGL 实现多 channel

Question

我在移植一些我在 Shadertoy 中成功实现的代码时遇到问题对于桌面 OpenGL，问题是我需要创建一个 FrameBufferObject FBO，以便我可以进行屏幕外计算，这些计算稍后将传递给主要的 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才能获得使其能够运行模拟的先前值。

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，然后将这些值传递给默认帧缓冲区:

// 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，您必须知道帧的编号是偶数还是奇数。
如果数字是偶数，则必须渲染到 textureColourBufferOne 并且渲染 channel 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 channel 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;

    .....
}