c-OpenGL实现MultiPass

2019-10-11 09:07:27 阅读：281 来源： 互联网

我在将一些已经在Shadertoy中成功实现的代码移植到桌面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,然后再将其传递给主要的glsl片段着色器,这是因为该缓冲区需要将自身作为纹理进行引用才能获得先前的值,以便它能够运行模拟.

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;

    }

但是我无法将缓冲区作为纹理呈现给它自己,我知道它会输出未定义的行为,因此我应该使用像乒乓球这样的技术.

有人可以指出我正确的方向吗？

解决方法:

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framebuffer对象,就像您对问题中的一个对象所做的那样：frameBufferOne和frameBufferTwo.
这2个帧缓冲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,您必须知道帧数是偶数还是奇数.
如果数字为偶数,则必须渲染到textureColourBufferOne,而渲染过程的输入是textureColourBufferTwo.
如果数字是奇数,则必须渲染到textureColourBufferTwo,渲染过程的输入是textureColourBufferOne.
渲染结果始终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;

    .....
}

标签：c,fragment-shader,opengl,glsl
来源： https://codeday.me/bug/20191011/1891392.html

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c-OpenGL实现MultiPass