OpenGL Hello Triangle Errors - c++

Question

I am trying to run the simple shaders to run; however when I try to run the code, I get an error saying "Exception thrown at 0x00000000 in OpenGL_Triangle.exe: 0xC0000005: Access violation executing location 0x00000000." in the separate loadShader file.
I tried running it underneath the GLEW initialization in my main file without using "GLuint LoadShaders(const char* vertex_file_path, const char* fragment_file_path){}" and "return ProgramID;" and defining LoadShaders as a separate unsigned int, and setting the "program" integer equal to the "ProgramID" integer from the loadShader file.
I don't exactly know what to do now.
*Just as a note I am using Visual Studio 2019.
//
// This is my main file (titled: main.cpp)
//
// Include standard headers
#include <stdio.h>
#include <stdlib.h>
#include <GL/glew.h>
#include <GLFW/glfw3.h>
#include <glm/glm.hpp>
using namespace glm;
#include <string>
#include <vector>
#include <fstream>
#include <algorithm>
#include <sstream>
#include <string.h>
#include <iostream>
using namespace std;
#include <common/shader.hpp>
// Create and compile our GLSL program from the shaders
GLuint program = LoadShaders("vertex.shader", "fragment.shader");
int main() {
// Initialise GLFW
glewExperimental = true; // Needed for core profile
if (!glfwInit())
{
cout << "Failed to initialize GLFW\n";
return -1;
}
cout << "Hello Triangle \n" ;
glfwWindowHint(GLFW_SAMPLES, 4); // 4x antialiasing
glfwWindowHint(GLFW_CONTEXT_VERSION_MAJOR, 4); // We want OpenGL 3.3
glfwWindowHint(GLFW_CONTEXT_VERSION_MINOR, 0);
glfwWindowHint(GLFW_OPENGL_FORWARD_COMPAT, GL_TRUE); // To make MacOS happy; should not be needed
glfwWindowHint(GLFW_OPENGL_PROFILE, GLFW_OPENGL_CORE_PROFILE); // We don't want the old OpenGL
// Open a window and create its OpenGL context
GLFWwindow* window; // (In the accompanying source code, this variable is global for simplicity)
window = glfwCreateWindow(500, 500, "Test", NULL, NULL);
if (window == NULL) {
cout << "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);
// Initialize GLEW
glewExperimental = true; // Needed in core profile
if (glewInit() != GLEW_OK) {
cout << "Failed to initialize GLEW from main\n";
return -1;
}
GLuint VertexArrayID;
glGenVertexArrays(1, &VertexArrayID);
glBindVertexArray(VertexArrayID);
// An array of 3 vectors which represents 3 vertices
static const GLfloat verts[] = {
-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(verts), verts, GL_STATIC_DRAW);
do {
// Clear the screen. It's not mentioned before Tutorial 02, but it can cause flickering, so it's there nonetheless.
glClear(GL_COLOR_BUFFER_BIT | GL_DEPTH_BUFFER_BIT);
// Use our shader
glUseProgram(program);
// Drawing
// 1st attribute buffer : vertices
glEnableVertexAttribArray(0);
glBindBuffer(GL_ARRAY_BUFFER, vertexbuffer);
glVertexAttribPointer(
0, // attribute 0. No particular reason for 0, but must match the layout in the shader.
3, // size
GL_FLOAT, // type
GL_FALSE, // normalized?
0, // stride
(void*)0 // array buffer offset
);
// Draw the triangle !
glDrawArrays(GL_TRIANGLES, 0, 3); // Starting from vertex 0; 3 vertices total -> 1 triangle
glDisableVertexAttribArray(0);
// Swap buffers
glfwSwapBuffers(window);
glfwPollEvents();
} // Check if the ESC key was pressed or the window was closed
while (glfwGetKey(window, GLFW_KEY_ESCAPE) != GLFW_PRESS &&
glfwWindowShouldClose(window) == 0);
}
//
// This is my LoadShaders file (titled: loadShader.cpp)
//
#include <stdio.h>
#include <string>
#include <vector>
#include <iostream>
#include <fstream>
#include <algorithm>
#include <sstream>
using namespace std;
#include <string.h>
#include <stdlib.h>
#include <GL/glew.h>
#include "common/shader.hpp"
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;
}
//
// This is the Shader header file (titled; shader.hpp)
// It was placed int the include directories folder in another folder titled "common"
//
#ifndef SHADER_HPP
#define SHADER_HPP
#include "GL/glew.h"
GLuint LoadShaders(const char* vertex_path, const char* fragment_path);
#endif

Answer 1

GLuint program = LoadShaders("vertex.shader", "fragment.shader");
int main() {
...
Don't try to execute GL commands before you have initialized GLEW. Otherwise you're going to call a NULL function-pointer like glCreateShader() and your process is Going To Have A Bad Time.
Move that LoadShaders() call to after glewInit().