c++ - 为 glm 翻译添加统一 vector 在 OpenGL 中不起作用

Question

如果我删除 uniform 变量和以下行:

//in CompileShaders function:
uniformModel = glGetUniformLocation(shader,"model"); 
  ...
//defined in the main draw loop after glfwPollEvents():
//and the shader has  compiled, linked and activated at this point
glm::mat4 modelMatrix;
modelMatrix = glm::translate(modelMatrix, glm::vec3(triOffset, 0.0f, 0.0f));
glUniformMatrix4fv(uniformModel, 1, GL_FALSE,glm::value_ptr(modelMatrix));  

程序显示正常，但是一旦我添加了统一变量并使用矩阵平移三角形，我就找不到为什么会出现红色屏幕，为了便于引用，着色器是:

static const char* vShader = 
"#version 330\n"
"layout (location = 0) in vec3 pos;\n"
"uniform mat4 model;\n"
"void main(){\n"
"   gl_Position = model * vec4(pos, 1.0);\n"
"}\n";

// fragment shader
static const char* fShader = ""
"#version 330\n"
"out vec4 color;\n"
"void main(){\n"
"   color = vec4(1.0, 1.0, 0.0, 1.0);\n"
"}\n";  

整个源码是:

#include <iostream>
#include <GL/glew.h>
#include <GLFW/glfw3.h>
#include <cmath>
#include <string.h>

#include "glm/glm.hpp"
#include "glm/gtc/matrix_transform.hpp"
#include "glm/gtc/type_ptr.hpp"


// Window Dimensions
const GLint WIDTH=800, HEIGHT=600;
GLuint VAO, VBO, shader;
GLint uniformModel {};
GLfloat triOffset {};
GLfloat triMaxOffset {5.0f};
bool direction = true;
// vertex shader
static const char* vShader = 
"#version 330\n"
"layout (location = 0) in vec3 pos;\n"
"uniform mat4 model;\n"
"void main(){\n"
"   gl_Position = model * vec4(pos, 1.0);\n"
"}\n";

// fragment shader
static const char* fShader = ""
"#version 330\n"
"out vec4 color;\n"
"void main(){\n"
"   color = vec4(1.0, 1.0, 0.0, 1.0);\n"
"}\n";

void AddShader(GLuint theProgram, const char* ShaderCode, GLenum shaderType, std::string info){
    std::cerr <<"DEBUG: Adding "<<info<<" Shader"<<std::endl;
    GLuint theShader = glCreateShader(shaderType);

    const GLchar* theCode[1];
    theCode[0] = ShaderCode;

    GLint codeLength[1];
    codeLength[0] = strlen(ShaderCode);

    glShaderSource(theShader, 1, theCode, codeLength);
    glCompileShader(theShader);

    GLint result =0;
    GLchar eLog[1024] ={0};

    glGetShaderiv(theShader, GL_COMPILE_STATUS, &result);
    if(!result){
        glGetShaderInfoLog(shader, sizeof(eLog), NULL, eLog);
        std::cerr<<"Error compiling program"<<std::endl;
        return;
    }
    glAttachShader(theProgram, theShader);

}

void CompileShader(){
    shader = glCreateProgram();
    if(!shader){
        std::cerr<<"Error creating shader"<<std::endl;
        return;
    }

    AddShader(shader, vShader, GL_VERTEX_SHADER, "vertex");
    AddShader(shader, fShader, GL_FRAGMENT_SHADER, "fragment");

    GLint result =0;
    GLchar eLog[1024] ={0};

    glLinkProgram(shader);
    glGetProgramiv(shader, GL_LINK_STATUS, &result);
    if(!result){
        glGetProgramInfoLog(shader, sizeof(eLog), NULL, eLog);
        std::cerr<<"Error linking program"<<std::endl;
        return;
    }

    glValidateProgram(shader);
    glGetProgramiv(shader, GL_VALIDATE_STATUS, &result);
    if(!result){
        glGetProgramInfoLog(shader, sizeof(eLog), NULL, eLog);
        std::cerr<<"Error Validating program"<<std::endl;
        return;
    }

    uniformModel = glGetUniformLocation(shader,"model");

}

void CreateTriangles(){
    GLfloat vertices[]={
        -1.0f, -1.0f, 0.0f,
        1.0f, -1.0f, 0.0f,
        0.0f, 1.0f, 0.0f
    };

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

        glGenBuffers(1, &VBO);
        glBindBuffer(GL_ARRAY_BUFFER, VBO);
        glBufferData(GL_ARRAY_BUFFER, sizeof(GLfloat)*9,vertices, GL_STATIC_DRAW);
        glVertexAttribPointer(0,3,GL_FLOAT,GL_FALSE,0,0);
        glEnableVertexAttribArray(0);

    glBindBuffer(GL_ARRAY_BUFFER, 0);
    glBindVertexArray(0);
}


int main(){
    //initialize GLFW
    if(!glfwInit()){
        std::cerr << "GLFW initialization failed!" << std::endl;
        glfwTerminate();
        return 1;
    }

    //Setup GLFW window properties
    //openGL version
    glfwWindowHint(GLFW_CONTEXT_VERSION_MAJOR, 3);
    glfwWindowHint(GLFW_CONTEXT_VERSION_MINOR, 3);
    // core profile = no backward compatibility
    glfwWindowHint(GLFW_OPENGL_PROFILE, GLFW_OPENGL_CORE_PROFILE);
    //allow forward compatibility
    glfwWindowHint(GLFW_OPENGL_FORWARD_COMPAT, GL_TRUE);

    GLFWwindow *mainWindow = glfwCreateWindow(WIDTH, HEIGHT, "TEST WINDOW", NULL, NULL);

    if(!mainWindow){
        std::cerr << "GLFW Window creation failed" << std::endl;
        glfwTerminate();
        return 1;
    }

    // get Buffer size information
    int bufferWidth, bufferHeight;
    glfwGetFramebufferSize(mainWindow, &bufferWidth, &bufferHeight);
    // set context for GLEW to use
    glfwMakeContextCurrent(mainWindow);

    // allow modern extension features

    if(glewInit()!=GLEW_OK){
        std::cerr << "GLEW initialization failed" << std::endl;
        glfwDestroyWindow(mainWindow);
        glfwTerminate();
        return 1;
    }

    // setup viewport size
    glViewport(0, 0, bufferWidth, bufferHeight);
    CreateTriangles();
    CompileShader();




    while(!glfwWindowShouldClose(mainWindow)){
        // get and handle user input events
        glfwPollEvents();

        glClearColor(1.0f, 0.0f, 0.0f, 1.0);
        glClear(GL_COLOR_BUFFER_BIT);

        if(direction){
            triOffset += 0.0005f;
        }else{
            triOffset -= 0.0005f;
            triOffset = abs(triOffset);
        }

        if(direction<=0.0 || direction> triMaxOffset){
            direction = !direction;
        }

        glUseProgram(shader);

        glm::mat4 modelMatrix;
        modelMatrix = glm::translate(modelMatrix, glm::vec3(triOffset, 0.0f, 0.0f));
        glUniformMatrix4fv(uniformModel, 1, GL_FALSE,glm::value_ptr(modelMatrix));
            glBindVertexArray(VAO);
                glDrawArrays(GL_TRIANGLES,0,3);
            glBindVertexArray(0);
        glUseProgram(0);
        // swap buffers
        glfwSwapBuffers(mainWindow);
    }


    return 0;
}  

如何确定问题所在？

Answer 1

模型矩阵变量 glm::mat4 modelMatrix 必须由 Identity matrix 初始化.

glm API documentation指The OpenGL Shading Language specification .

5.4.2 Vector and Matrix Constructors

If there is a single scalar parameter to a vector constructor, it is used to initialize all components of the constructed vector to that scalar’s value. If there is a single scalar parameter to a matrix constructor, it is used to initialize all the components on the matrix’s diagonal, with the remaining components initialized to 0.0.

安Identity matrix可以通过单个参数 1.0 初始化:

glm::mat4 modelMatrix(1.0f);