When I tried to run this I got a "Segmentation fault (core dumped) error and nothing ran:
#include <stdio.h>
#include <stdlib.h>
#include <GL/glew.h>
#include <GLFW/glfw3.h>
#include <glm/glm.hpp>
#include </home/rohan/Documents/opengl/common/loadShader.hpp>
using namespace glm;
int main() {
glewExperimental = true;
if ( !glfwInit() )
{
fprintf(stderr, "Failed to initialize GLFW\n");
return -1;
}
glfwWindowHint(GLFW_SAMPLES, 4); // 4x antialiasing
glfwWindowHint(GLFW_CONTEXT_VERSION_MAJOR, 3); // We want OpenGL 3.3
glfwWindowHint(GLFW_CONTEXT_VERSION_MINOR, 3);
glfwWindowHint(GLFW_OPENGL_FORWARD_COMPAT, GL_TRUE); // To make MacOS happy; should not be needed
glfwWindowHint(GLFW_OPENGL_PROFILE, GLFW_OPENGL_CORE_PROFILE);
GLuint VertexArrayID;
glGenVertexArrays(1, &VertexArrayID);
glBindVertexArray(VertexArrayID);
// An array of 3 vectors which represents 3 vertices
static const GLfloat g_vertex_buffer_data[] = {
-1.0f, -1.0f, 0.0f,
1.0f, -1.0f, 0.0f,
0.0f, 1.0f, 0.0f,
};
// This will identify our vertex buffer
GLuint vertexbuffer;
// Generate 1 buffer, put the resulting identifier in vertexbuffer
glGenBuffers(1, &vertexbuffer);
// The following commands will talk about our 'vertexbuffer' buffer
glBindBuffer(GL_ARRAY_BUFFER, vertexbuffer);
// Give our vertices to OpenGL.
glBufferData(GL_ARRAY_BUFFER, sizeof(g_vertex_buffer_data), g_vertex_buffer_data, GL_STATIC_DRAW);
GLFWwindow* window;
window = glfwCreateWindow(1024, 768, "Tutorial 01", NULL, NULL);
if (window == NULL)
{
fprintf(stderr, "Failed to open GLFW window.If you have an Intel GPU, they are not 3.3 compatible. Try the 2.1 version of the tutorials.\n" );
glfwTerminate();
return -1;
}
glfwMakeContextCurrent(window);
glewExperimental=true;
if (glewInit() != GLEW_OK)
{
fprintf(stderr, "Failed to initialize GLEW\n");
return -1;
}
glfwSetInputMode(window, GLFW_STICKY_KEYS, GL_TRUE);
// Create and compile our GLSL program from the shaders
GLuint programID = LoadShaders( "SimpleVertexShader.glsl", "SimpleFragmentShader.glsl" );
do{
glClear(GL_COLOR_BUFFER_BIT | GL_DEPTH_BUFFER_BIT);
// 1st attribute buffer : vertices
glEnableVertexAttribArray(0);
glBindBuffer(GL_ARRAY_BUFFER, vertexbuffer);
glVertexAttribPointer(
// unknown, size, type, normalized?, stride, array buffer offset
0, 3, GL_FLOAT, GL_FALSE, 0, (void*)0);
// Use our shader
glUseProgram(programID);
// Draw the triangle !
glDrawArrays(GL_TRIANGLES, 0, 3); // Starting from vertex 0; 3 vertices total -> 1 triangle
glDisableVertexAttribArray(0);
glfwSwapBuffers(window);
glfwPollEvents();
}
while(glfwGetKey(window, GLFW_KEY_ESCAPE) != GLFW_PRESS && glfwWindowShouldClose(window) == 0);
}
vertex shader
#version 330 core
layout(location = 0) in vec3 vertexPosition_modelspace;
void main()
{
gl_Position.xyz = vertexPosition_modelspace;
gl_Position.w = 1.0;
}
fragment shader:
#version 330 core
out vec3 color;
void main()
{
color = vec3(1,0,0);
}
shader-loader:
#include <string>
#include <fstream>
#include <sstream>
#include <vector>
GLuint LoadShaders(const char * vertex_file_path,const char * fragment_file_path){
// Create the shaders
GLuint VertexShaderID = glCreateShader(GL_VERTEX_SHADER);
GLuint FragmentShaderID = glCreateShader(GL_FRAGMENT_SHADER);
// Read the Vertex Shader code from the file
std::string VertexShaderCode;
std::ifstream VertexShaderStream(vertex_file_path, std::ios::in);
if(VertexShaderStream.is_open()){
std::stringstream sstr;
sstr << VertexShaderStream.rdbuf();
VertexShaderCode = sstr.str();
VertexShaderStream.close();
}else{
printf("Impossible to open %s. Are you in the right directory ? Don't forget to read the FAQ !\n", vertex_file_path);
getchar();
return 0;
}
// Read the Fragment Shader code from the file
std::string FragmentShaderCode;
std::ifstream FragmentShaderStream(fragment_file_path, std::ios::in);
if(FragmentShaderStream.is_open()){
std::stringstream sstr;
sstr << FragmentShaderStream.rdbuf();
FragmentShaderCode = sstr.str();
FragmentShaderStream.close();
}
GLint Result = GL_FALSE;
int InfoLogLength;
// Compile Vertex Shader
printf("Compiling shader : %s\n", vertex_file_path);
char const * VertexSourcePointer = VertexShaderCode.c_str();
glShaderSource(VertexShaderID, 1, &VertexSourcePointer , NULL);
glCompileShader(VertexShaderID);
// Check Vertex Shader
glGetShaderiv(VertexShaderID, GL_COMPILE_STATUS, &Result);
glGetShaderiv(VertexShaderID, GL_INFO_LOG_LENGTH, &InfoLogLength);
if ( InfoLogLength > 0 ){
std::vector<char> VertexShaderErrorMessage(InfoLogLength+1);
glGetShaderInfoLog(VertexShaderID, InfoLogLength, NULL, &VertexShaderErrorMessage[0]);
printf("%s\n", &VertexShaderErrorMessage[0]);
}
// Compile Fragment Shader
printf("Compiling shader : %s\n", fragment_file_path);
char const * FragmentSourcePointer = FragmentShaderCode.c_str();
glShaderSource(FragmentShaderID, 1, &FragmentSourcePointer , NULL);
glCompileShader(FragmentShaderID);
// Check Fragment Shader
glGetShaderiv(FragmentShaderID, GL_COMPILE_STATUS, &Result);
glGetShaderiv(FragmentShaderID, GL_INFO_LOG_LENGTH, &InfoLogLength);
if ( InfoLogLength > 0 ){
std::vector<char> FragmentShaderErrorMessage(InfoLogLength+1);
glGetShaderInfoLog(FragmentShaderID, InfoLogLength, NULL, &FragmentShaderErrorMessage[0]);
printf("%s\n", &FragmentShaderErrorMessage[0]);
}
// Link the program
printf("Linking program\n");
GLuint ProgramID = glCreateProgram();
glAttachShader(ProgramID, VertexShaderID);
glAttachShader(ProgramID, FragmentShaderID);
glLinkProgram(ProgramID);
// Check the program
glGetProgramiv(ProgramID, GL_LINK_STATUS, &Result);
glGetProgramiv(ProgramID, GL_INFO_LOG_LENGTH, &InfoLogLength);
if ( InfoLogLength > 0 ){
std::vector<char> ProgramErrorMessage(InfoLogLength+1);
glGetProgramInfoLog(ProgramID, InfoLogLength, NULL, &ProgramErrorMessage[0]);
printf("%s\n", &ProgramErrorMessage[0]);
}
glDetachShader(ProgramID, VertexShaderID);
glDetachShader(ProgramID, FragmentShaderID);
glDeleteShader(VertexShaderID);
glDeleteShader(FragmentShaderID);
return ProgramID;
}
The code is supposed to make a red triangle appear.
To call an OpenGL instruction, you need a valid and current OpenGL context and the OpenGL loader (in your case glew) must be in initialized. Therefore you cannot do the vertex specification before glewInit. Move all OpenGL commands after that:
// [...]
glfwMakeContextCurrent(window);
if (glewInit() != GLEW_OK)
{
fprintf(stderr, "Failed to initialize GLEW\n");
return -1;
}
// The earliest point for calling an OpenGL (gl*) instruction is here
// [...]
Note, glewExperimental = True is not further necessary (see Initializing GLEW).