c++ - OpenGL 累积缓冲区不工作

Question

我正在尝试在 OpenGL 中使用累积缓冲区，但由于某种原因，缓冲区似乎没有被填充。我构建了一个简单的测试应用程序，一个正在渲染的 2D 平面，仅此而已。这很好。然后我尝试做我能想到的最简单的累积缓冲区操作，将渲染帧加载到累积缓冲区，清除屏幕，然后将累积缓冲区返回到屏幕。当我这样做时，累积缓冲区似乎根本不包含任何信息，图像只是屏幕被清除的颜色，就好像累积缓冲区根本没有返回一样。我还尝试过进行更传统的运动模糊设置，在返回之前对场景和缓冲区进行多次更新并获得相同的结果。

这是简单测试的主循环:

SDL_Event eve;
while (true)
{
    //Normal stuff
    glClear(GL_COLOR_BUFFER_BIT | GL_DEPTH_BUFFER_BIT);

    glDrawElements(GL_TRIANGLES, 6, GL_UNSIGNED_INT, 0);

    //Accumulation///////////////////////
    glAccum(GL_LOAD, 1.0f);

    glClear(GL_COLOR_BUFFER_BIT | GL_DEPTH_BUFFER_BIT);

    glAccum(GL_RETURN, 1.0f);
    //Accumulation///////////////////////

    SDL_GL_SwapWindow(window);

    SDL_PollEvent(&eve);
}

这是运动模糊测试的主循环:

float x = 0.0f;

int step = 0;
int steps = 4;

SDL_Event eve;
while (true)
{
    //Test stuff
    x += 0.005f;

    GLfloat newVerts[] = {
        -0.5f + x,  0.5f,
        0.5f + x,  0.5f,
        0.5f + x, -0.5f,
        -0.5f + x, -0.5f,
    };

    glBufferData(GL_ARRAY_BUFFER, sizeof(newVerts), newVerts, GL_STATIC_DRAW);

    //Normal stuff
    glClear(GL_COLOR_BUFFER_BIT | GL_DEPTH_BUFFER_BIT);

    glDrawElements(GL_TRIANGLES, 6, GL_UNSIGNED_INT, 0);

    //Accumulation///////////////////////
    if (step == 0)
    {
        glAccum(GL_LOAD, 1.0f / steps);
    }
    else
    {
        glAccum(GL_ACCUM, 1.0f / steps);
    }

    step++;

    if (step < steps)
    {
        continue;
    }

    step = 0;
    glAccum(GL_RETURN, 1.0f);
    //Accumulation///////////////////////

    SDL_GL_SwapWindow(window);

    SDL_PollEvent(&eve);
}

这是完整的应用程序源代码(它只有大约 100 行，我将其包括在内只是为了防止我的 glEnable 或 SDL_GL_SetAttribute 调用出现问题):

#include "tools.h"

static string vertexSource = getFile("D:/test.vsh");
static string fragmentSource = getFile("D:/test.fsh");

int main(int argc, char *argv[])
{
    //SDL///////////////////////////////////////////////
    SDL_Init(SDL_INIT_EVERYTHING);

    SDL_GL_SetAttribute(SDL_GL_CONTEXT_MAJOR_VERSION, 4);
    SDL_GL_SetAttribute(SDL_GL_CONTEXT_MINOR_VERSION, 5);
    SDL_GL_SetAttribute(SDL_GL_CONTEXT_PROFILE_MASK, SDL_GL_CONTEXT_PROFILE_CORE);

    SDL_GL_SetAttribute(SDL_GL_RED_SIZE, 8);
    SDL_GL_SetAttribute(SDL_GL_GREEN_SIZE, 8);
    SDL_GL_SetAttribute(SDL_GL_BLUE_SIZE, 8);
    SDL_GL_SetAttribute(SDL_GL_ALPHA_SIZE, 8);

    SDL_GL_SetAttribute(SDL_GL_ACCUM_RED_SIZE, 8);
    SDL_GL_SetAttribute(SDL_GL_ACCUM_GREEN_SIZE, 8);
    SDL_GL_SetAttribute(SDL_GL_ACCUM_BLUE_SIZE, 8);
    SDL_GL_SetAttribute(SDL_GL_ACCUM_ALPHA_SIZE, 8);

    SDL_Window *window = SDL_CreateWindow("Test", 50, 50, 1600, 900, SDL_WINDOW_OPENGL | SDL_WINDOW_RESIZABLE);

    SDL_GLContext context = SDL_GL_CreateContext(window);

    //GLEW///////////////////////////////////////////////
    glewExperimental = GL_TRUE;
    GLint result = glewInit();

    if (result != GLEW_OK)
    {
        cout << glewGetErrorString(result) << "\n";
        cout << "GLEW initialization failed.\n";
    }

    //OpenGL///////////////////////////////////////////////
    glEnable(GL_DEPTH);
    glDepthFunc(GL_LEQUAL);
    glEnable(GL_DEPTH_TEST);

    glEnable(GL_BLEND);
    glBlendFunc(GL_SRC_ALPHA, GL_ONE_MINUS_SRC_ALPHA);

    glClearColor(1.0f, 1.0f, 0.0f, 1.0f);
    glClearDepth(1.0f);

    //Object///////////////////////////////////////////

    //Vertex Array
    GLuint vao;
    glGenVertexArrays(1, &vao);
    glBindVertexArray(vao);

    //Vertex Buffer
    GLuint vbo;
    glGenBuffers(1, &vbo);

    GLfloat vertices[] = {
        -0.5f,  0.5f,
        0.5f,  0.5f,
        0.5f, -0.5f,
        -0.5f, -0.5f,
    };

    glBindBuffer(GL_ARRAY_BUFFER, vbo);
    glBufferData(GL_ARRAY_BUFFER, sizeof(vertices), vertices, GL_STATIC_DRAW);

    //Element Buffer
    GLuint ebo;
    glGenBuffers(1, &ebo);

    GLuint elements[] = {
        0, 1, 2,
        2, 3, 0
    };

    glBindBuffer(GL_ELEMENT_ARRAY_BUFFER, ebo);
    glBufferData(GL_ELEMENT_ARRAY_BUFFER, sizeof(elements), elements, GL_STATIC_DRAW);

    //Shader
    GLuint shaderProgram = createShader(vertexSource, fragmentSource);
    glUseProgram(shaderProgram);

    GLint posAttrib = glGetAttribLocation(shaderProgram, "position");
    glEnableVertexAttribArray(posAttrib);
    glVertexAttribPointer(posAttrib, 2, GL_FLOAT, GL_FALSE, 0, 0);

    //Loop///////////////////////////////////////////////
    float x = 0.0f;

    int step = 0;
    int steps = 4;

    SDL_Event eve;
    while (true)
    {
        //Test stuff
        x += 0.005f;

        GLfloat newVerts[] = {
            -0.5f + x,  0.5f,
            0.5f + x,  0.5f,
            0.5f + x, -0.5f,
            -0.5f + x, -0.5f,
        };

        glBufferData(GL_ARRAY_BUFFER, sizeof(newVerts), newVerts, GL_STATIC_DRAW);

        //Normal stuff
        glClear(GL_COLOR_BUFFER_BIT | GL_DEPTH_BUFFER_BIT);

        glDrawElements(GL_TRIANGLES, 6, GL_UNSIGNED_INT, 0);

        //Accumulation///////////////////////
        if (step == 0)
        {
            glAccum(GL_LOAD, 1.0f / steps);
        }
        else
        {
            glAccum(GL_ACCUM, 1.0f / steps);
        }

        step++;

        if (step < steps)
        {
            continue;
        }

        step = 0;
        glAccum(GL_RETURN, 1.0f);
        //Accumulation///////////////////////

        SDL_GL_SwapWindow(window);

        SDL_PollEvent(&eve);
    }
}

我使用 GLEW 访问 OpenGL 调用，我使用 SDL 进行上下文创建和窗口管理。

我运行此平台的一般规范:

• OpenGL 4.5(也尝试过 4.3 和 3.3，没有区别)。
• Windows 10 64 位
• AMD FX-9590 @ 4.7 GHz
• 英伟达 GTX 970 SC
• 华硕剑齿虎 990FX
• 16GB DDR3 内存

Answer 1

SDL_GL_SetAttribute(SDL_GL_CONTEXT_PROFILE_MASK, SDL_GL_CONTEXT_PROFILE_CORE);
                                                 ^^^^^^^^^^^^^^^^^^^^^^^^^^^

移除的功能(如累积缓冲区)在 Core 上下文中不起作用。

OpenGL 3.2 Core spec, appendix E, page 329 & 333:

E.2 Deprecated and Removed Features

...

Functions which have been removed will generate an INVALID_OPERATIONerror if called in the core profile or in a forward-compatible context.

...

E.2.2 Removed Features

...

Accumulation buffers - ClearAccum, and ACCUM_BUFFER_BIT is not valid as a bit in the argument to Clear (section 4.2.3); Accum; the ACCUM_*_-BITS framebuffer state describing the size of accumulation buffer components; and all associated state.

Window system-binding APIs such as GLX and WGL may choose to either not expose window configs containing accumulation buffers, or to ignore accumulation buffers when the default framebuffer bound to a GL context contains them.