启用深度测试时的二维文本工件 Opengl

Posted 2023-02-22

【中文标题】启用深度测试时的二维文本工件 Opengl

【英文标题】：2d text artifact when depth test is enable Opengl

【发布时间】：2020-12-20 12:57:51

【问题描述】：

Main.cpp

//Variables
const unsigned int width = 896, height = 504;

//Initiating GLFW Window
glfwInit();
glfwWindowHint(GLFW_CONTEXT_VERSION_MAJOR, 3);
glfwWindowHint(GLFW_CONTEXT_VERSION_MINOR, 3);
glfwWindowHint(GLFW_OPENGL_PROFILE, GLFW_OPENGL_CORE_PROFILE);

//Creating a GLFW window
window = glfwCreateWindow(width, height, "Jaguar", NULL, NULL);

//Checking if Window was initiated
if (window == NULL) 
    std::cout << "GLFW FAILED TO INITIATE WINDOW!\n";
    glfwTerminate();


glfwMakeContextCurrent(window);

//Centering Window 
int windowWidth, windowHeight;
glfwGetWindowSize(window, &windowWidth, &windowHeight);
const GLFWvidmode* mode = glfwGetVideoMode(glfwGetPrimaryMonitor());
glfwSetWindowPos(window, mode->width / 2 - windowWidth / 2, mode->height / 2 - windowHeight / 2);

//Setting-Up window's icon
GLFWimage icon[1];
icon[0].pixels = stbi_load("resources/images/gui/icon/icon.png", &icon[0].width, &icon[0].height, 0, 4);
glfwSetWindowIcon(window, 1, icon);
stbi_image_free(icon[0].pixels);

//Checking if Glad was initiated
if (!gladLoadGLLoader((GLADloadproc)glfwGetProcAddress)) 
    std::cout << "GLAD FAILED TO BE INITIATED\n";


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

stbi_set_flip_vertically_on_load(true);

//Setting-Up Viewport
glViewport(0, 0, width, height);

//Intitiating MainMenu
states.push(new MainMenuState(*window, &states));

字体.cpp

FT_Library ft;

if (FT_Init_FreeType(&ft)) 
    std::cout << "FREETYPE::Failed to initialize library\n";

FT_Face face;
if (FT_New_Face(ft, filePath, 0, &face)) 
    std::cout << "FREETYPE::Failed to load to font: " << filePath << "\n";


// set size to load glyphs as
FT_Set_Pixel_Sizes(face, 0, px);

glPixelStorei(GL_UNPACK_ALIGNMENT, 1);

for (unsigned char c = 0; c < 128; c++) 

    if (FT_Load_Char(face, c, FT_LOAD_RENDER)) 
        std::cout << "FREETYPE::Failed to load glpyh\n";
    
    unsigned int texture;
    glGenTextures(1, &texture);
    glBindTexture(GL_TEXTURE_2D, texture);
    glTexImage2D(GL_TEXTURE_2D, 0, GL_RED, face->glyph->bitmap.width,
        face->glyph->bitmap.rows, 0, GL_RED, GL_UNSIGNED_BYTE,
        face->glyph->bitmap.buffer);

    glTexParameteri(GL_TEXTURE_2D, GL_TEXTURE_WRAP_S, GL_CLAMP_TO_BORDER);
    glTexParameteri(GL_TEXTURE_2D, GL_TEXTURE_WRAP_T, GL_CLAMP_TO_BORDER);
    glTexParameteri(GL_TEXTURE_2D, GL_TEXTURE_MIN_FILTER, GL_LINEAR);
    glTexParameteri(GL_TEXTURE_2D, GL_TEXTURE_MAG_FILTER, GL_LINEAR);

    Character character = 
    texture,
    glm::ivec2(face->glyph->bitmap.width, face->glyph->bitmap.rows),
    glm::ivec2(face->glyph->bitmap_left, face->glyph->bitmap_top)
    ,face->glyph->advance.x ;

    Characters.insert(std::pair<char, Character>(c, character));

FT_Done_Face(face);
FT_Done_FreeType(ft);

文本.cpp

// activate corresponding render state  
shader.use();
glUniform3f(glGetUniformLocation(shader.id, "textColor"), color.x, color.y, 
color.z);
glActiveTexture(GL_TEXTURE0);
glBindVertexArray(VAO);

// iterate through all characters
std::string::const_iterator c;
for (c = string.begin(); c != string.end(); c++)

   
    Character ch = font.Characters[*c];
   
    float xpos = position.x + ch.bearing.x * scale;
    float ypos = position.y - (ch.size.y - ch.bearing.y) * scale;

    float w = ch.size.x * scale;
    float h = ch.size.y * scale;
    // update VBO for each character
    float vertices[6][4] = 
         xpos,     ypos + h,   0.0f, 0.0f ,
         xpos,     ypos,       0.0f, 1.0f ,
         xpos + w, ypos,       1.0f, 1.0f ,

         xpos,     ypos + h,   0.0f, 0.0f ,
         xpos + w, ypos,       1.0f, 1.0f ,
         xpos + w, ypos + h,   1.0f, 0.0f 
    ;
    // render glyph texture over quad
    glBindTexture(GL_TEXTURE_2D, ch.textureId);
    // update content of VBO memory
    glBindBuffer(GL_ARRAY_BUFFER, VBO);
    glBufferSubData(GL_ARRAY_BUFFER, 0, sizeof(vertices), vertices);
    glBindBuffer(GL_ARRAY_BUFFER, 0);
    // render quad
    glDrawArrays(GL_TRIANGLES, 0, 6);
    // now advance cursors for next glyph (note that advance is number of 
1/64 pixels)
    position.x += (ch.advance >> 6) * scale; // bitshift by 6 to get value in 
pixels (2^6 = 64)

glBindVertexArray(0);
glBindTexture(GL_TEXTURE_2D, 0);

我已经做过的事情：

最后渲染文本 使用 gl_src_alpha, gl_one_minus_src_alpha

当我禁用深度测试时，它工作得很好，我只是在需要时启用和禁用吗？ 如果是这样，在性能（游戏流畅度）方面有多差/多好

我对此进行了一些研究，人们说启用 alpha 混合是指 gl_src_alpha、gl_one_minus_src_alpha

【参考方案1】：

当您使用Blending 时，您必须禁用Depth Test。绘制几何图形时启用深度测试，但在绘制文本之前禁用深度测试。深度测试会导致根据深度函数丢弃片段。混合从片段着色器获取片段颜色输出，并将它们与颜色缓冲区中的颜色组合。因此混合只适用于那些没有被丢弃的片段。