glClearColor 和混合

Posted 2023-02-22

【中文标题】glClearColor 和混合

【英文标题】：glClearColor and blending

【发布时间】：2021-02-10 09:25:33

【问题描述】：

我正在使用 GLFW、带有 VSCode 的 OpenGL 4.6 和 MinGW64 g++。我正在尝试使用glEnable(GL_BLEND); 和glBlendFunc(GL_SRC_ALPHA, GL_ONE_MINUS_SRC1_ALPHA); 渲染透明纹理。虽然纹理确实在我的窗口上呈现，但 glClearColor() 似乎显着影响了混合。我对图形还是很陌生，所以我不确定如何正确渲染纹理，无论清晰的颜色设置为什么。另外，我需要为 2D 游戏启用深度吗？ （shader.cpp 和 texture.cpp 取自 The Cherno 的 OpenGL 教程系列）

没有混合

与混合

具有混合和黑色透明色（所需混合）

main.cpp:

#include <GL/glew.h>
#include <GLFW/glfw3.h>
#include <glm/glm.hpp>
#include <glm/gtc/matrix_transform.hpp>
#include "GeometryUtil.h"
#include "Shader.h"
#include "Texture.h"
#include "Object.h"

#include <iostream>
#include <vector>

using namespace std;

int main() 
    if (!glfwInit())  // Initialise GLFW
        cerr << "Failed to initialize GLFW" << endl;
        return -1;
    

    glfwWindowHint(GLFW_SAMPLES, 4);
    glfwWindowHint(GLFW_CONTEXT_VERSION_MAJOR, 4);
    glfwWindowHint(GLFW_CONTEXT_VERSION_MINOR, 6);
    glfwWindowHint(GLFW_OPENGL_PROFILE, GLFW_OPENGL_CORE_PROFILE);

    GLFWwindow* window glfwCreateWindow(1280, 720, "2D GAME", NULL, NULL);
    if (window == NULL) 
        cerr << "Failed to open GLFW window." << endl;
        glfwTerminate();
        return -1;
    

    glfwSetInputMode(window, GLFW_STICKY_KEYS, GL_TRUE);
    glfwMakeContextCurrent(window);

    glewExperimental = true;
    if (glewInit() != GLEW_OK) 
        cerr << "Failed to initialize GLEW" << endl;
        glfwTerminate();
        return -1;
    
    
    cout << "OpenGL Version: " << glGetString(GL_VERSION) << endl;
    glEnable(GL_DEPTH_TEST);
    glDepthFunc(GL_LESS);
    glEnable(GL_BLEND);
    glBlendFunc(GL_SRC_ALPHA, GL_ONE_MINUS_SRC1_ALPHA);
    glClearColor(0.0f, 1.0f, 0.0f, 1.0f);

    GLuint VAO;
    glGenVertexArrays(1, &VAO);
    glBindVertexArray(VAO);

    Object object 608, 392;
    vector<float> vectorData;
    createQuad(object.getX(), object.getY(), vectorData);

    static const GLfloat texCoords[8] 
        0.0f, 1.0f,
        1.0f, 1.0f,
        0.0f, 0.0f,
        1.0f, 0.0f
    ;

    GLuint VBOs[2];
    glGenBuffers(2, VBOs);
    glBindBuffer(GL_ARRAY_BUFFER, VBOs[0]);
    glBufferData(GL_ARRAY_BUFFER, vectorData.size() * sizeof(vectorData), &vectorData.front(), GL_DYNAMIC_DRAW);
    glEnableVertexAttribArray(0);
    glVertexAttribPointer(0, 2, GL_FLOAT, GL_FALSE, 3 * sizeof(GLfloat), (void *) 0);
    glEnableVertexAttribArray(2);
    glVertexAttribPointer(2, 1, GL_FLOAT, GL_FALSE, 3 * sizeof(GLfloat), (void *) (2 * sizeof(GLfloat)));

    glBindBuffer(GL_ARRAY_BUFFER, VBOs[1]);
    glBufferData(GL_ARRAY_BUFFER, sizeof(texCoords), texCoords, GL_STATIC_DRAW);
    glEnableVertexAttribArray(1);
    glVertexAttribPointer(1, 2, GL_FLOAT, GL_FALSE, 0, nullptr);
    

    static const GLuint texIndex[6] 
        0,  1,  2,
        1,  2,  3
    ;
    GLuint indexBuffer;
    glGenBuffers(1, &indexBuffer);
    glBindBuffer(GL_ELEMENT_ARRAY_BUFFER, indexBuffer);
    glBufferData(GL_ELEMENT_ARRAY_BUFFER, 6 * sizeof(texIndex), texIndex, GL_STATIC_DRAW);

    glm::mat4 Projection glm::ortho(0.0f, 1280.0f, 0.0f, 720.0f, 0.0f, 1.0f);
    glm::mat4 View glm::translate(glm::mat4(1.0f), glm::vec3(0, 0, 0));

    glm::vec3 translationA glm::vec3(0, 0, 0);
    glm::mat4 Model = glm::translate(glm::mat4(1.0f), translationA); // Model Matrix (Using Identity Matrix - Origin)
    glm::mat4 mvp = Projection * View * Model;

    Shader shader "shader/vertexShader.vert", "shader/fragmentShader.frag";
    shader.bind();
    shader.setUniformMat4f("MVP", mvp);
    int sampler[] 0, 1;
    shader.setUniform1iv("v_Textures", sampler, 2);

    Texture texture "resources/sprites/test.png";
    texture.bind();

    while (glfwGetKey(window, GLFW_KEY_ESCAPE) != GLFW_PRESS && glfwWindowShouldClose(window) == 0) 
        glClear(GL_COLOR_BUFFER_BIT | GL_DEPTH_BUFFER_BIT);

        glDrawElements(GL_TRIANGLES, 6, GL_UNSIGNED_INT, nullptr);

        glfwSwapBuffers(window);
        glfwPollEvents();
    
    glfwTerminate();
    return 0;

纹理.cpp：

#define STB_IMAGE_IMPLEMENTATION
#include <GL/glew.h>
#include "Texture.h"
#include "stb_image.h"

#include <iostream>

Texture::Texture(const std::string &path) 
    : rendererID0, filePathpath, localBuffernullptr, width0, height0, bPP0 
        // stbi_set_flip_vertically_on_load(1);
        localBuffer = stbi_load(path.c_str(), &width, &height, &bPP, 4);
        if (localBuffer == nullptr)
            std::cout << "Unable to load texture file: " << path << std::endl;

        glGenTextures(1, &rendererID);
        glBindTexture(GL_TEXTURE_2D, rendererID);

        glTexParameteri(GL_TEXTURE_2D, GL_TEXTURE_MIN_FILTER, GL_LINEAR);
        glTexParameteri(GL_TEXTURE_2D, GL_TEXTURE_MAG_FILTER, GL_LINEAR);
        glTexParameteri(GL_TEXTURE_2D, GL_TEXTURE_WRAP_S, GL_CLAMP_TO_EDGE);
        glTexParameteri(GL_TEXTURE_2D, GL_TEXTURE_WRAP_T, GL_CLAMP_TO_EDGE);
        glTexImage2D(GL_TEXTURE_2D, 0, GL_RGBA8, width, height, 0, GL_RGBA, GL_UNSIGNED_BYTE, localBuffer);

        unbind();

        if (localBuffer)
            stbi_image_free(localBuffer);

Texture::~Texture() 
    glDeleteTextures(1, &rendererID);


void Texture::bind(GLuint slot) const ;
    glActiveTexture(GL_TEXTURE0 + slot);
    glBindTexture(GL_TEXTURE_2D, rendererID);

void Texture::unbind() const 
    glBindTexture(GL_TEXTURE_2D, 0);

顶点着色器：

#version 460 core

layout(location = 0) in vec3 vertexCoords;
layout(location = 1) in vec2 textureCoords;
layout(location = 2) in float textureIndex;

out vec2 v_TexCoords;
out float v_TexIndex;

uniform mat4 MVP;

void main() 
    gl_Position = MVP * vec4(vertexCoords, 1.0);
    v_TexCoords = textureCoords;
    v_TexIndex = textureIndex;

片段着色器：

#version 460 core

in vec2 v_TexCoords;
in float v_TexIndex;

uniform sampler2D v_Textures[2];

void main() 
    gl_FragColor = texture2D(v_Textures[int(v_TexIndex)], v_TexCoords);

【问题讨论】：

这是预期的结果。混合的工作方式是将您输出的颜色与缓冲区中已有的颜色混合。如果您的 C 字母的 alpha 值小于 1，它将与背景颜色组合，从而对其进行着色。这与 alpha-keying 不同，您可以根据值丢弃样本，但不将它们与缓冲区中已有的数据结合起来。

【参考方案1】：

乍一看，一切都是正确的代码，是的，在GL_SRC_ALPHA作为第一个参数的情况下，背景会影响混合。

问题是第二个参数应该是GL_ONE_MINUS_SRC_ALPHA 而不是GL_ONE_MINUS_SRC1_ALPHA。在您的情况下，混合没有标准化，因此过多的绿色和全红色的值加起来就是黄色。

来源：https://www.khronos.org/registry/OpenGL-Refpages/gl4/html/glBlendFuncSeparate.xhtml