OpenGL实现MultiPass

Question

我很难将我在着色玩具中成功实现的一些代码移植到桌面OpenGL，问题是我需要创建一个FrameBufferObject FBO，这样我就可以进行屏幕外的计算，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引用自己作为纹理来获得以前的值，以便能够运行模拟。

我已经成功地创建了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Render循环中调用它，以便可以将这些值呈现给FBO，然后将这些值传递给默认的Framebuffer：

// 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;

    }

但我无法将缓冲区呈现为纹理，我理解它输出未定义的行为，并且我应该使用一种技术，如乒乓。

谁能给我指明正确的方向吗？

Answer 1

但我无法将缓冲区呈现为纹理，我理解它输出未定义的行为，并且我应该使用一种技术，如乒乓。 谁能给我指明正确的方向吗？

您必须创建两个framebuffer对象，就像您使用问题中的一个对象一样：frameBufferOne和frameBufferTwo。

这两个框架缓冲区对象的每个对象都必须附加一个纹理对象：textureColourBufferOne和textureColourBufferTwo。

在程序的主循环中，您必须知道帧的数目是偶数还是奇数。

如果数字是偶数，则必须将其呈现给textureColourBufferOne，而呈现传递的输入是textureColourBufferTwo。

如果数字是奇数，则必须将其呈现给textureColourBufferTwo，而呈现传递的输入是textureColourBufferOne。

呈现的结果总是存储在属于当前帧的框架缓冲区的纹理中：

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;

    .....
}