为什么模板测试不丢弃片段？

Question

我想运行模板测试来勾勒立方体的轮廓。来自learnopengl https://learnopengl.com/Advanced-OpenGL/Stencil-testing。

做轮廓处理的立方体应该丢弃了纹理立方体上的碎片。它不会发生，轮廓立方体覆盖了整个区域。

static const char* cubeVtx = R"(
#version 460 core
layout (location = 0) in vec3 a_position;
layout (location = 1) in vec2 a_uv;

out vec2 v_uv;

uniform mat4 model;
uniform mat4 view;
uniform mat4 projection;

void main()
{
    v_uv = a_uv;    
    gl_Position = projection * view * model * vec4(a_position, 1.0f);
}

)";

static const char* cubeFrag = R"(
#version 460 core

layout (location = 0) out vec4 f_color;

in vec2 v_uv;

uniform sampler2D u_texture1;

void main()
{    
    f_color = texture(u_texture1, v_uv);
}

)";

static const char* singleColorVtx = R"(
#version 460 core
layout (location = 0) in vec3 a_position;

uniform mat4 model;
uniform mat4 view;
uniform mat4 projection;

void main()
{   
    gl_Position = projection * view * model * vec4(a_position, 1.0f);
}

)";

static const char* singleColorFrag = R"(
#version 460 core

layout (location = 0) out vec4 f_color;

void main()
{    
    f_color = vec4(1.0f, 0.0f, 0.0f, 1.0f);
}

)";

void Cube::InitAPI()
{
    shader = Shader::Create();
    ShaderProgram program[2] = {
        shader->ShaderFromSource(cubeVtx, ShaderType::Vertex),
        shader->ShaderFromSource(cubeFrag, ShaderType::Fragment)
    };
    shader->End(program, 2);

    singleColorShader = Shader::Create();
    ShaderProgram singleColorProgram[2] = {
        singleColorShader->ShaderFromSource(singleColorVtx, ShaderType::Vertex),
        singleColorShader->ShaderFromSource(singleColorFrag, ShaderType::Fragment)
    };
    singleColorShader->End(singleColorProgram, 2);

    glCreateVertexArrays(1, &vao);
    glBindVertexArray(vao);
    glCreateBuffers(1, &vbo);
    glBindBuffer(GL_ARRAY_BUFFER, vbo);
    glNamedBufferData(vbo, sizeof(cubeVertices), cubeVertices, GL_STATIC_DRAW);

    glEnableVertexAttribArray(0);
    glEnableVertexAttribArray(1);
    glVertexAttribPointer(0, 3, GL_FLOAT, false, 5 * sizeof(float), 0);
    glVertexAttribPointer(1, 2, GL_FLOAT, false, 5 * sizeof(float), (void*)(3 * sizeof(float)));

    glCreateVertexArrays(1, &planeVao);
    glBindVertexArray(planeVao);
    glCreateBuffers(1, &planeVbo);
    glBindBuffer(GL_ARRAY_BUFFER, planeVbo);
    glNamedBufferData(planeVbo, sizeof(planeVertices), planeVertices, GL_STATIC_DRAW);

    glEnableVertexAttribArray(0);
    glEnableVertexAttribArray(1);
    glVertexAttribPointer(0, 3, GL_FLOAT, false, 5 * sizeof(float), 0);
    glVertexAttribPointer(1, 2, GL_FLOAT, false, 5 * sizeof(float), (void*)(3 * sizeof(float)));

    texture = Texture::LoadPNG("Media/container2");
    planeTexture = Texture::LoadPNG("Media/matrix");

    glEnable(GL_DEPTH_TEST);
    glDepthFunc(GL_LESS);
    glEnable(GL_STENCIL_TEST);
    glStencilFunc(GL_NOTEQUAL, 1, 0xFF);
    glStencilOp(GL_KEEP, GL_KEEP, GL_REPLACE);

    shader->UseProgram();
    shader->Uniform1i("u_texture1", 0);
}

void Cube::Render()
{
    singleColorShader->UseProgram();
    glm::mat4 model = glm::mat4(1.0f);
    glm::mat4 view = camera.GetViewMatrix();
    glm::mat4 projection = glm::perspective(glm::radians(camera.Zoom), (float)1280.0f / (float)720.0f, 0.1f, 100.0f);
    singleColorShader->UniformMatrix4fv("view", view);
    singleColorShader->UniformMatrix4fv("projection", projection);

    shader->UseProgram();
    shader->UniformMatrix4fv("view", view);
    shader->UniformMatrix4fv("projection", projection);

    glStencilMask(0x00);
    glBindVertexArray(planeVao);
    planeTexture->Active();
    planeTexture->Bind();
    glDrawArrays(GL_TRIANGLES, 0, 6);

    glStencilFunc(GL_ALWAYS, 1, 0xFF);
    glStencilMask(0xFF);

    glBindVertexArray(vao);
    model = glm::translate(model, glm::vec3(-1.0f, 0.0f, -1.0f));
    shader->UniformMatrix4fv("model", model);
    texture->Active();
    texture->Bind();
    glDrawArrays(GL_TRIANGLES, 0, 36);

    model = glm::mat4(1.0f);
    model = glm::translate(model, glm::vec3(2.0f, 0.0f, 0.0f));
    shader->UniformMatrix4fv("model", model);
    glDrawArrays(GL_TRIANGLES, 0, 36);

    glStencilFunc(GL_NOTEQUAL, 1, 0xFF);
    glStencilMask(0x00);
    glDisable(GL_DEPTH_TEST);
    singleColorShader->UseProgram();
    float scale = 1.1;

    glBindVertexArray(vao);
    model = glm::mat4(1.0f);
    model = glm::translate(model, glm::vec3(-1.0f, 0.0f, -1.0f));
    model = glm::scale(model, glm::vec3(scale, scale, scale));
    shader->UniformMatrix4fv("model", model);
    glDrawArrays(GL_TRIANGLES, 0, 36);

    model = glm::mat4(1.0f);
    model = glm::translate(model, glm::vec3(2.0f, 0.0f, 0.0f));
    model = glm::scale(model, glm::vec3(scale, scale, scale));
    shader->UniformMatrix4fv("model", model);
    glDrawArrays(GL_TRIANGLES, 0, 36);

    glBindVertexArray(0);

    glStencilMask(0xFF);
    glEnable(GL_DEPTH_TEST);
}

Test::Test()
{
    //tried many patterns and stencil values

    SDL_GL_SetAttribute(SDL_GL_CONTEXT_PROFILE_MASK, SDL_GL_CONTEXT_PROFILE_CORE);
    SDL_GL_SetAttribute(SDL_GL_CONTEXT_MAJOR_VERSION, 4);
    SDL_GL_SetAttribute(SDL_GL_CONTEXT_MINOR_VERSION, 6);
    SDL_GL_SetAttribute(SDL_GL_DOUBLEBUFFER, 1);

    SDL_GL_SetAttribute(SDL_GL_STENCIL_SIZE, 8);
    window = SDL_CreateWindow("window", SDL_WINDOWPOS_CENTERED, SDL_WINDOWPOS_CENTERED, 1280, 720, SDL_WINDOW_OPENGL);

    context = SDL_GL_CreateContext(window);
    SDL_GL_MakeCurrent(window, context);

    glewExperimental = true;
    glewInit();

    cube.InitAPI();
}

void Test::MainLoop()
{
    while (!quit) {
        while (SDL_PollEvent(&event)) {
            if (event.type == SDL_QUIT) {
                quit = true;
            }
        }

        glClearColor(0.5f, 0.5f, 0.5f, 1.0f);
        glClear(GL_COLOR_BUFFER_BIT | GL_DEPTH_BUFFER_BIT | GL_STENCIL_BUFFER_BIT);

        cube.Render();

        SDL_GL_SwapWindow(window);
    }
}

我仍然不太明白深度测试的事情，当我开始认为我正在进行模板测试时，一切都搞砸了，因为它不起作用。

是的，我在其他地方清除颜色、深度和模板缓冲区，但在 Render() 方法之前。

我得到了什么：

我期望的是红色轮廓，而不是整个立方体

你能像我是个白痴一样解释一下为什么它不丢弃 1

的片段吗

Answer 1

先调用 SDL_Init，再调用任何其他 SDL-function

SDL_Init(SDL_INIT_EVERYTHING);

参见 SDL_Init() 的文档：

Use this function to initialize the SDL library. This must be called before using most other SDL functions.

要使模板缓冲区工作，必须设置 SDL_GL_STENCIL_SIZE 属性。默认情况下，此属性为 0。通常，模板缓冲区有 8 位。例如：

SDL_GL_SetAttribute(SDL_GL_STENCIL_SIZE, 8);

SDL_GL_SetAttribute has to be called before SDL_CreateWindow否则没有任何作用

参见SDL_GL_SetAttribute的文档：

Use this function to set an OpenGL window attribute before window creation.

Answer 2

原始代码在SDL_GL_SetAttribute()之后调用SDL_Init 上面的代码甚至没有调用 SDL_Init。初始化 SDL 可以解决所有问题。

为什么模板测试不丢弃片段？

Why stencil test does not discard fragments?

c++

opengl

stencil-buffer