GLSL 从我的制服中取回奇怪的值，它似乎也设置了错误的值

Question

我在顶点着色器中使用 uniform 时遇到问题

代码如下

// gcc main.c -o main `pkg-config --libs --cflags glfw3` -lGL -lm


#include <GLFW/glfw3.h>
#include <stdio.h>
#include <stdlib.h>
#include <math.h>

void gluErrorString(const char* why,GLenum errorCode);
void checkShader(GLuint status, GLuint shader, const char* which);


float verts[] = {
    -0.5f,   0.5f,   0.0f,
     0.5f,   0.5f,   0.0f,
     0.5f,  -0.5f,   0.0f,
    -0.5f,  -0.5f,   0.0f
};

const char* vertex_shader =
    "#version 330\n"
    "in vec3 vp;\n"
    "uniform float u_time;\n"
    "\n"
    "void main () {\n"
    "  vec4 p = vec4(vp, 1.0);\n"
    "  p.x = p.x + u_time;\n"
    "  gl_Position = p;\n"
    "}";

const char* fragment_shader =
    "#version 330\n"
    "out vec4 frag_colour;\n"
    "void main () {\n"
    "  frag_colour = vec4 (0.5, 0.0, 0.5, 1.0);\n"
    "}";




int main () {

    if (!glfwInit ()) {
        fprintf (stderr, "ERROR: could not start GLFW3\n");
        return 1;
    }

    glfwWindowHint (GLFW_CONTEXT_VERSION_MAJOR, 3);
    glfwWindowHint (GLFW_CONTEXT_VERSION_MINOR, 2);
    //glfwWindowHint (GLFW_OPENGL_FORWARD_COMPAT, GL_TRUE);
    glfwWindowHint (GLFW_OPENGL_PROFILE, GLFW_OPENGL_CORE_PROFILE);

    GLFWwindow* window = glfwCreateWindow (640, 480, "Hello Triangle", NULL, NULL);
    if (!window) {
        fprintf (stderr, "ERROR: could not open window with GLFW3\n");
        glfwTerminate();
        return 1;
    }

    glfwMakeContextCurrent (window);

    // vert arrays group vert buffers together unlike GLES2 (no vert arrays)
    // we *must* have one of these even if we only need 1 vert buffer
    GLuint vao = 0;
    glGenVertexArrays (1, &vao);
    glBindVertexArray (vao);

    GLuint vbo = 0;
    glGenBuffers (1, &vbo);
    glBindBuffer (GL_ARRAY_BUFFER, vbo);
    // each vert takes 3 float * 4 verts in the fan = 12 floats
    glBufferData (GL_ARRAY_BUFFER, 12 * sizeof (float), verts, GL_STATIC_DRAW);
    gluErrorString("buffer data",glGetError());

    glEnableVertexAttribArray (0);
    glBindBuffer (GL_ARRAY_BUFFER, vbo);
    // 3 components per vert
    glVertexAttribPointer (0, 3, GL_FLOAT, GL_FALSE, 0, NULL);
    gluErrorString("attrib pointer",glGetError());


    GLuint vs = glCreateShader (GL_VERTEX_SHADER);
    glShaderSource (vs, 1, &vertex_shader, NULL);
    glCompileShader (vs);
    GLint success = 0;
    glGetShaderiv(vs, GL_COMPILE_STATUS, &success);
    checkShader(success, vs, "Vert Shader");

    GLuint fs = glCreateShader (GL_FRAGMENT_SHADER);
    glShaderSource (fs, 1, &fragment_shader, NULL);
    glCompileShader (fs);
    glGetShaderiv(fs, GL_COMPILE_STATUS, &success);
    checkShader(success, fs, "Frag Shader"); 

    GLuint shader_program = glCreateProgram ();
    glAttachShader (shader_program, fs);
    glAttachShader (shader_program, vs);
    glLinkProgram (shader_program);
    gluErrorString("Link prog",glGetError());

    glUseProgram (shader_program);
    gluErrorString("use prog",glGetError());


    GLuint uniT = glGetUniformLocation(shader_program,"u_time"); // ask gl to assign uniform id
    gluErrorString("get uniform location",glGetError());    

    printf("uniT=%i\n",uniT);

    glEnable (GL_DEPTH_TEST);
    glDepthFunc (GL_LESS);
    float t=0;



    while (!glfwWindowShouldClose (window)) {

        glClear (GL_COLOR_BUFFER_BIT | GL_DEPTH_BUFFER_BIT);
        gluErrorString("clear",glGetError());

        glUseProgram (shader_program);
        gluErrorString("use prog",glGetError());

        t=t+0.01f;
        glUniform1f( uniT, (GLfloat)sin(t));
        gluErrorString("set uniform",glGetError());

        float val;
        glGetUniformfv(shader_program,  uniT,  &val);
        gluErrorString("get uniform",glGetError());
        printf("val=%f ",val);

        glBindVertexArray (vao);
        gluErrorString("bind array",glGetError());

        glDrawArrays (GL_TRIANGLE_FAN, 0, 4);
        gluErrorString("draw arrays",glGetError());

        glfwPollEvents ();
        glfwSwapBuffers (window);
        gluErrorString("swap buffers",glGetError());
    }

    glfwTerminate();
    return 0;
}


void checkShader(GLuint status, GLuint shader, const char* which) {
    if (status==GL_TRUE) return;
    int length;
    char buffer[1024];
    glGetShaderInfoLog(shader, sizeof(buffer), &length, buffer);
    fprintf (stderr,"%s Error: %s\n", which,buffer);
    glfwTerminate();
    exit(-1);
}

struct token_string
{
    GLuint Token;
    const char *String;
};

static const struct token_string Errors[] = {
    { GL_NO_ERROR, "no error" },
    { GL_INVALID_ENUM, "invalid enumerant" },
    { GL_INVALID_VALUE, "invalid value" },
    { GL_INVALID_OPERATION, "invalid operation" },
    { GL_STACK_OVERFLOW, "stack overflow" },
    { GL_STACK_UNDERFLOW, "stack underflow" },
    { GL_OUT_OF_MEMORY, "out of memory" },
    { GL_TABLE_TOO_LARGE, "table too large" },
#ifdef GL_EXT_framebuffer_object
    { GL_INVALID_FRAMEBUFFER_OPERATION_EXT, "invalid framebuffer operation" },
#endif

    { ~0, NULL } /* end of list indicator */
};

void gluErrorString(const char* why,GLenum errorCode)
{
    if (errorCode== GL_NO_ERROR) return;
    int i;
    for (i = 0; Errors[i].String; i++) {
        if (Errors[i].Token == errorCode) { 
            fprintf (stderr,"error: %s - %s\n",why,Errors[i].String);
            glfwTerminate();
            exit(-1);            
        }
    }

}

当代码运行时，四边形闪烁，就好像制服正在获取垃圾值，同时获取制服的值显示一些奇怪的值，如 36893488147419103232.000000，它应该只是一个简单的正弦值

Answer 1

您的代码问题仅与 GL 间接相关 - 您的 GL 代码没有问题。

但是，您使用的是现代 OpenGL 函数，而没有将函数指针作为扩展加载。这可能适用于某些平台，但不适用于其他平台。 MacOS 确实保证这些函数在系统的 GL 库中导出。在 windows 上，Microsoft opengl32.dll 从不包含 GL 1.1 以外的功能 - 您的代码不会 link 在那里。在 Linux，你介于两者之间。只有 this old Linux OpenGL ABI document，保证 OpenGL 1.2 函数必须由库导出。实际上，Linux 上的大多数 GL 实现的库都导出所有内容（但该功能存在并不意味着它受支持）。但是你永远不应该直接 link 这些功能，因为没有人保证任何事情。

然而，故事并没有就此结束：您显然是在导出符号的实现上这样做的。但是，您没有包含正确的 headers。而且您的编译器设置很差。在 C 中，调用之前未声明的函数是有效的（但风格很差）。编译器将假定它 returns int 并且所有参数都是 ints。实际上，您正在调用这些函数，但编译器会将参数转换为 int。

您会注意到，如果您将编译器设置为产生一些警告，例如 gcc 上的 -Wall：

a.c: In function ‘main’:
a.c:74: warning: implicit declaration of function ‘glGenVertexArrays’
a.c:75: warning: implicit declaration of function ‘glBindVertexArray’
[...]

但是，代码编译和 links，我可以重现你描述的结果（我在这里使用 Linux/Nvidia）。

要解决此问题，您应该使用 OpenGL Loader Library. For example, I got your code working by using GLEW。我所要做的就是在文件的最顶部添加

#define GLEW_NO_GLU // because you re-implemented some glu-like functions with a different interface
#include <glew.h>

正在打电话

glewExperimental=GL_TRUE;
if (glewInit() != GLEW_OK) {
    fprintf (stderr, "ERROR: failed to initialize GLEW\n");
    glfwTerminate();
    return 1;
}
glGetError(); // read away error generated by GLEW, it is broken in core profiles...

GLEW headers 包含所有函数的声明，因此不再发生隐式类型转换。 GLEW 可能不是核心配置文件的最佳选择，但我只是使用它，因为这是我最熟悉的加载器。

GLSL 从我的制服中取回奇怪的值，它似乎也设置了错误的值

GLSL getting odd values back from my uniform and it seems to be set with the wrong value too

opengl

glsl