我在顶点着色器中使用制服时遇到问题
继承人的代码
// 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，好像制服得到垃圾值，同时获得制服的值显示一些奇数值，如36893488147419103232.000000，它应该只是一个简单的正弦值
答案 0 :(得分：2)
您的代码问题只与GL间接相关 - 您的GL代码没问题。
但是，您使用现代OpenGL函数而不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确保这些函数在系统的GL库中导出。在Windows上，微软opengl32.dll从不包含GL 1.1以外的功能 - 您的代码不会链接到那里。在Linux上，你介于两者之间。只有this old Linux OpenGL ABI document，它保证了必须由库导出OpenGL 1.2函数。在实践中，大多数GL实现的Linux上的库都会导出所有内容（但是函数存在的事实并不意味着它被支持）。但是你永远不应该直接链接这些功能，因为没有人保证任何东西。
然而，故事并没有在这里结束：你显然在导出符号的实现上做了这个。但是，您没有包含正确的标头。而且你的编译器设置得很差。在C中，调用之前未声明的函数是有效的（但风格很差）。编译器将确认它返回int 并且所有参数都是int s 。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，如果您设置了编译器以产生一些警告，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’
[...]
然而，代码编译和链接，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。例如，我使用GLEW使您的代码正常工作。我所要做的只是在文件顶部添加
#define GLEW_NO_GLU // because you re-implemented some glu-like functions with a different interface
#include <glew.h>
并致电
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头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，因为那是我最熟悉的加载器。