glClearColor 和混合

Question

我正在使用 GLFW、带 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 window 上渲染，但似乎 glClearColor() 对混合有显着影响。我对图形还是很陌生，所以我不确定如何正确渲染纹理，而不管清晰颜色设置为什么。另外，我需要为 2D 游戏启用 Depth 吗？（shader.cpp 和 texture.cpp 摘自 The Cherno 的 OpenGL 教程系列）

没有混合

混合

使用混合色和黑色透明色（所需混合色）

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;
}

texture.cpp:

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

#include <iostream>

Texture::Texture(const std::string &path) 
    : rendererID{0}, filePath{path}, localBuffer{nullptr}, width{0}, height{0}, bPP{0} {
        // 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);
}

Answer 1

乍一看，一切代码都是正确的，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，混合未标准化，因此太多绿色和全红色的值加起来会偏黄。

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

glClearColor 和混合

glClearColor and blending

c++

opengl

blending

glfw