Why do i have to call gladLoadGL() after glfwMakeContextCurrent()? - c++

Hello it took me two days to figure out why my window always closed instand.
It was because i called gladLoadGL(glfwGetProcAddress) before glfwMakeContextCurrent(window).
This does NOT work:
int main() {
glfwInit();
glfwWindowHint(GLFW_CONTEXT_VERSION_MINOR, 3);
glfwWindowHint(GLFW_CONTEXT_VERSION_MAJOR, 3);
glfwWindowHint(GLFW_OPENGL_PROFILE, GLFW_OPENGL_CORE_PROFILE);
gladLoadGL(glfwGetProcAddress);
GLFWwindow * window = glfwCreateWindow(600, 600, "agag", NULL, NULL);
glfwMakeContextCurrent(window);
while (!glfwWindowShouldClose(window)) {
glClear(GL_COLOR_BUFFER_BIT);
glClearColor(0.2f, 0.5f, 0.6f, 1);
glfwSwapBuffers(window);
glfwPollEvents();
}
glfwTerminate();
}
But when i call gladLoadGL(glfwGetProcAddress); AFTER glfwMakeContextCurrent(window); it DOES work!
Do i have load glad everytime i am switching the window? (maybe later i have to)
But is it really like that or is it a bug?
When i write it before glfwMakeContextCurrent the error:
-1073741819 (0xC0000005)
comes up.

Related

Why is OpenGL GLFW Rendering shapes not working?

I am trying to get started with openGL and GLFW in c++. My expectation is that the following code will simply render a square on the screen, but I just get a black screen.
The actual setup is working though, because if I add glClearColor(0.1f, 0.4f, 0.8f, 1.0f);, I do indeed get a blue screen. But what is wrong with my use of GL_QUADS?
#include <iostream>
// GLEW
#define GLEW_STATIC
#include <GL/glew.h>
//GLFW
#include <GLFW/glfw3.h>
const GLint WIDTH = 800, HEIGHT = 600;
int main() {
glfwInit();
glfwWindowHint( GLFW_CONTEXT_VERSION_MAJOR, 3);
glfwWindowHint( GLFW_CONTEXT_VERSION_MINOR, 3);
glfwWindowHint( GLFW_OPENGL_PROFILE, GLFW_OPENGL_CORE_PROFILE);
glfwWindowHint( GLFW_OPENGL_FORWARD_COMPAT, GL_TRUE);
glfwWindowHint( GLFW_RESIZABLE, GL_TRUE);
GLFWwindow *window = glfwCreateWindow(WIDTH, HEIGHT, "Isosurface Stuffing", nullptr, nullptr);
int screenWidth, screenHeight;
glfwGetFramebufferSize(window, &screenWidth, &screenHeight);
if (window == nullptr) {
std::cout << "Failed to create GLFW window" << std::endl;
glfwTerminate();
return -1;
}
glfwMakeContextCurrent(window);
glewExperimental = GL_TRUE;
if (GLEW_OK != glewInit()) {
std::cout << "Failed to create GLEW" << std::endl;
return -1;
}
while (!glfwWindowShouldClose(window)) {
glClear(GL_COLOR_BUFFER_BIT | GL_DEPTH_BUFFER_BIT);
glLoadIdentity();
glViewport(0, 0, screenWidth, screenHeight);
glMatrixMode(GL_PROJECTION);
glLoadIdentity();
glOrtho(0.0f, screenWidth, 0.0f, screenHeight, 0.0f, 1.0f);
glMatrixMode (GL_MODELVIEW);
glLoadIdentity();
glfwPollEvents();
glColor3f(0.5f, 0.5f, 0.5f);
glBegin(GL_QUADS);
glVertex2f(100, 100);
glVertex2f(200, 100);
glVertex2f(200, 200);
glVertex2f(100, 200);
glEnd();
glfwSwapBuffers(window);
}
glfwTerminate();
return 0;
}
You cannot use the legacy fixed-function pipeline instructions (glBegin, glEnd, glVertex2f, glMatrixMode, glLoadIdentity, glOrtho) in a Core profile OpenGL context (GLFW_OPENGL_CORE_PROFILE). You have to use Compatibility profile OpenGL Context:
glfwWindowHint( GLFW_OPENGL_PROFILE, GLFW_OPENGL_CORE_PROFILE);
glfwWindowHint(GLFW_OPENGL_PROFILE, GLFW_OPENGL_COMPAT_PROFILE);
If your system does not allow you to create a compatibility profile context (e.g. Mac), you must use either an OpenGL 2.0 context or a modern OpenGL with Shaders and Vertex Array Objects. A nice tutorial for that is LearnOpenGL

Why is my opengl triangle code producing a black screen?

#include <iostream>
#include <GL/glew.h>
#include <GLFW/glfw3.h>
int main(void)
{
GLFWwindow* window;
/* Initialize the library */
if (!glfwInit())
return -1;
glfwWindowHint(GLFW_CONTEXT_VERSION_MAJOR, 3);
glfwWindowHint(GLFW_CONTEXT_VERSION_MINOR, 3);
glfwWindowHint(GLFW_OPENGL_PROFILE, GLFW_OPENGL_CORE_PROFILE);
/* Create a windowed mode window and its OpenGL context */
window = glfwCreateWindow(640, 480, "Hello World", NULL, NULL);
if (!window)
{
glfwTerminate();
return -1;
}
glfwMakeContextCurrent(window);
glewExperimental = true;
glewInit();
while (!glfwWindowShouldClose(window))
{
glClearColor(1.0f, 0.0f, 1.0f, 1.0f);
glClear(GL_COLOR_BUFFER_BIT);
std::cout << glGetError() << std::endl;
glBegin(GL_TRIANGLES);
glVertex2f(-0.5f, -0.5f);
glVertex2f(0.5f, -0.5f);
glVertex2f(0.0f, 0.5f);
glEnd();
glfwSwapBuffers(window);
glfwPollEvents();
}
glfwTerminate();
return 0;
}
Despite setting glClearColor, only a black screen is shown. Drawing the triangle doesn't work either, and glGetError returns 0 everywhere. What am I doing wrong?
(I know this is a legacy way to render a triangle, I'm just trying to test if opengl is working, and apparently, it isn't.)
You cannot use the legacy OpenGL (glBegin/glEnd sequences) with a Core profile OpenGL Context (GLFW_OPENGL_CORE_PROFILE) you must use a Compatibility profile OpenGL context (GLFW_OPENGL_COMPAT_PROFILE):
glfwWindowHint(GLFW_OPENGL_PROFILE, GLFW_OPENGL_CORE_PROFILE);
glfwWindowHint(GLFW_OPENGL_PROFILE, GLFW_OPENGL_COMPAT_PROFILE);

why does linker error keep happening even though I set the AdditionalDependencies already?

I was following the OpenGL tutorial from Freecodecamp.org (https://www.youtube.com/watch?v=45MIykWJ-C4) and I got this error while following the "Window" part of the tutorial.
#include <iostream>
#include <glad/glad.h>
#include <GLFW/glfw3.h>
int main()
{
glfwInit();
glfwWindowHint(GLFW_CONTEXT_VERSION_MAJOR, 3);
glfwWindowHint(GLFW_CONTEXT_VERSION_MINOR, 3);
glfwWindowHint(GLFW_OPENGL_PROFILE, GLFW_OPENGL_CORE_PROFILE);
GLFWwindow* window = glfwCreateWindow(800, 800, "openGLTest", NULL, NULL);
if (window == NULL)
{
std::cout << "Failed to create GLFW window" << std::endl;
glfwTerminate();
return -1;
}
glfwMakeContextCurrent(window);
gladLoadGL();
glViewport(0, 0, 800, 800); //error starts when I wrote this
glClearColor(0.07f, 0.13f, 0.17f, 1.0f);
glClear(GL_COLOR_BUFFER_BIT);
glfwSwapBuffers(window);
while (!glfwWindowShouldClose(window))
{
glfwPollEvents();
}
glfwDestroyWindow(window);
glfwTerminate();
return 0;
}
This error keeps happening even though my Additional Dependencies is set to glfw3.lib;opengl32.lib;%(AdditionalDependencies).

glClearColor is ignored

I am trying to set the background color to blue, but glClearColor is completely ignored.
Code:
glfwWindowHint(GLFW_RESIZABLE, GL_FALSE);
GLFWwindow* window = glfwCreateWindow(640, 480, "3D Shooter", NULL, NULL);
glClearColor(0.5f, 0.5f, 1.0f, 1.0f);
while (!glfwWindowShouldClose(window)) {
glClear(GL_COLOR_BUFFER_BIT);
glfwSwapBuffers(window);
glfwPollEvents();
}
You seem to be missing a
glfwMakeContextCurrent(window);
https://www.glfw.org/docs/3.3/quick.html

OpenGL GLFW window closes as soon as it opens

I have problem in seeing my triangle in a black window. The window though just closes as it opens, and does not allow me to see what's going on inside it. I have seen somewhere on the net that i has something to do with the minor-versioning, of which I have no clue how to check on my VGA card.
Here is my full code:
#define GLEW_STATIC
#include <stdio.h>
#include <GL\glew.h>
#include <GL\GLU.h>
#include <GL\glut.h>
#include <glm.hpp>
#include <GL\gl.h>
#include <GLFW\glfw3.h>
using namespace glm;
using namespace std;
int main()
{
glfwWindowHint(GLFW_SAMPLES, 4); // anti aliasing
glfwWindowHint(GLFW_CONTEXT_VERSION_MAJOR, 3); // openGL major version to be 3
glfwWindowHint(GLFW_CONTEXT_VERSION_MINOR, 0); // minor set to 3, which makes the version 3.3
glfwWindowHint(GLFW_OPENGL_FORWARD_COMPAT, GL_TRUE); // for MAC OS only
glfwWindowHint(GLFW_OPENGL_COMPAT_PROFILE, GLFW_OPENGL_CORE_PROFILE); //avoid using old openGL
GLFWwindow* window;
window = glfwCreateWindow(1024, 768, "First Window in OpenGL", 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);
GLuint VertexArrayID;
glGenVertexArrays(1, &VertexArrayID);
glBindVertexArray(VertexArrayID);
static const GLfloat g_vertex_buffer_data[] = {
-1.0f, -1.0f, 0.0f,
1.0f, -1.0f, 0.0,
0.0f, 1.0f, 0.0f
};
// identifying our vertex buffer
GLuint 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);
glewExperimental = true; // Needed in core profile
if (glewInit() != GLEW_OK)
{
fprintf(stderr, "Failed to initialize GLEW\n");
return -1;
}
glfwSetInputMode(window, GLFW_STICKY_KEYS, GL_TRUE);
do{
// 1rst 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
);
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);
return 0;
}
Can anyone please help me on keeping the window open and just close it with ESC key as it is expected from the code?
The reason the window closes immediately is because you have a segmentation fault.
This is most likely due to failing to initialize things in proper order.
Initialize GLFW before running any glfw function calls, like so:
// Initialise GLFW
if( !glfwInit() ) {
fprintf( stderr, "Failed to initialize GLFW\n" );
return -1;
}
glfwWindowHint(GLFW_SAMPLES, 4); // anti aliasing
glfwWindowHint(GLFW_CONTEXT_VERSION_MAJOR, 3); // openGL major version to be 3
glfwWindowHint(GLFW_CONTEXT_VERSION_MINOR, 0); // minor set to 3, which makes the version 3.3
glfwWindowHint(GLFW_OPENGL_FORWARD_COMPAT, GL_TRUE); // for MAC OS only
glfwWindowHint(GLFW_OPENGL_COMPAT_PROFILE, GLFW_OPENGL_CORE_PROFILE); //avoid using old openGL
GLFWwindow* window;
window = gl
Then, move the initialization of glew to right after you create and set the GL context:
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 = GL_TRUE; // Needed in core profile
const GLenum err = glewInit();
if (err != GLEW_OK) {
fprintf(stderr, "Failed to initialize GLEW\n");
fprintf(stderr, "Error: %s\n", glewGetErrorString(err));
return -1;
}
GLuint VertexArrayID;
glGenVertexArrays(1, &VertexArrayID);
glBindVertexArray(VertexArrayID);
// ... rest of code follows
I have tested it, and your code should work fine now, and the window won't close until you hit ESC.