glClearColor is ignored - c++

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

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);

Window not closing GLFW

I am writing a game engine in OpenGL and GLFW. However, somehow my window can't be closed. I tried many things but it doesn't have effect. What's wrong with my code?
I can't find the wrong thing in it - everything seems fine to me.
Code:
int running;
GLFWwindow* window;
Window::~Window()
{
glfwTerminate();
}
Window::Window(int width, int height, const std::string& title)
: m_width(width),
m_height(height),
m_title(title){
glfwInit();
if (!glfwInit())
glfwWindowHint(GLFW_RESIZABLE, GL_FALSE);
window = glfwCreateWindow(height, width, __FILE__, NULL, NULL);
if (!window) {
glfwTerminate();
}
running = true;
}
void Window::MainLoop()
{
do
{
glfwMakeContextCurrent(window);
glClearColor(0.2f, 0.3f, 0.3f, 1.0f);
glClear(GL_COLOR_BUFFER_BIT);
glFlush();
glfwPollEvents();
Draw();
glfwSwapBuffers(window);
}
while(running);
}
void Window::Draw()
{
glBegin(GL_TRIANGLES);
glVertex3f( 0.0f, 1.0f, 0.0f);
glVertex3f( 1.0f,-1.0f, 0.0f);
glVertex3f(-1.0f,-1.0f, 0.0f);
glEnd();
}
Thanks!
There are several things but the issue seems to be that you never set running = false.
Try making your while condition looking like this while(!glfwWindowShouldClose(window));
Also if you would like to be able to close the window by pressing escape this should work: while(!glfwWindowShouldClose(window) && glfwGetKey(window_, GLFW_KEY_ESCAPE) != GLFW_PRESS);
Also consider making your int running a bool.
And things such as glfwMakeContextCurrent(window); and glClearColor(0.2f, 0.3f, 0.3f, 1.0f); do not need to be inside your loop if you do not intend to change them.
For more information about openGL and to gain some basic understanding and working examples consider reading https://learnopengl.com/.

OpenGL and GLFW: Not drawing polygon

I am able to create a window and clear it to the desired color. But not able to draw a square in the lower left hand corner.
#include <iostream>
#define GLEW_STATIC
#include <GL/glew.h>
#include <GLFW/glfw3.h>
const GLint WIDTH = 720;
const GLint HEIGHT = 480;
int main()
{
glfwInit();
glfwWindowHint(GLFW_CONTEXT_VERSION_MAJOR, 3); // Attempts to set to opengl 3.3
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, "Learn OpenGL", nullptr, nullptr);
int screenWidth, screenHeight;
glfwGetFramebufferSize(window, &screenWidth, &screenHeight);
if (nullptr == window)
{
std::cout << "Failed to create GLFW window" << std::endl;
glfwTerminate();
return EXIT_FAILURE;
}
glfwMakeContextCurrent(window);
glewExperimental = GL_TRUE;
if (GLEW_OK != glewInit())
{
std::cout << "Failed to initialise GLEW" << std::endl;
return EXIT_FAILURE;
}
glViewport(0, 0, screenWidth, screenHeight);
while (!glfwWindowShouldClose(window))
{
glClearColor(1.0f, 0.0f, 0.0f, 1.0f);
glClear(GL_COLOR_BUFFER_BIT);
glColor3f(0.0f, 0.0f, 1.0f);
glOrtho(0.0, 1.0, 0.0, 1.0, -1.0, 1.0);
glBegin(GL_POLYGON);
glVertex3f(0.0, 0.0, 0.0);
glVertex3f(0.5, 0.0, 0.0);
glVertex3f(0.5, 0.5, 0.0);
glVertex3f(0.0, 0.5, 0.0);
glEnd();
glFlush();
glfwSwapBuffers(window);
glfwPollEvents();
}
glfwTerminate();
return EXIT_SUCCESS;
}
Deprecated fixed-function functionality (glBegin() et al & the matrix stacks) doesn't work in a Core context (GLFW_OPENGL_CORE_PROFILE).
Switch to a Compatibility context:
#include <iostream>
#include <GL/glew.h>
#include <GLFW/glfw3.h>
const GLint WIDTH = 720;
const GLint HEIGHT = 480;
int main()
{
glfwInit();
glfwWindowHint(GLFW_RESIZABLE, GL_TRUE);
GLFWwindow *window = glfwCreateWindow(WIDTH, HEIGHT, "Learn OpenGL", nullptr, nullptr);
int screenWidth, screenHeight;
glfwGetFramebufferSize(window, &screenWidth, &screenHeight);
if (nullptr == window)
{
std::cout << "Failed to create GLFW window" << std::endl;
glfwTerminate();
return EXIT_FAILURE;
}
glfwMakeContextCurrent(window);
glewExperimental = GL_TRUE;
if (GLEW_OK != glewInit())
{
std::cout << "Failed to initialise GLEW" << std::endl;
return EXIT_FAILURE;
}
glViewport(0, 0, screenWidth, screenHeight);
while (!glfwWindowShouldClose(window))
{
glClearColor(1.0f, 0.0f, 0.0f, 1.0f);
glClear(GL_COLOR_BUFFER_BIT);
glMatrixMode( GL_PROJECTION );
glLoadIdentity();
glOrtho(0.0, 1.0, 0.0, 1.0, -1.0, 1.0);
glMatrixMode( GL_MODELVIEW );
glLoadIdentity();
glColor3f(0.0f, 0.0f, 1.0f);
glBegin(GL_POLYGON);
glVertex3f(0.0, 0.0, 0.0);
glVertex3f(0.5, 0.0, 0.0);
glVertex3f(0.5, 0.5, 0.0);
glVertex3f(0.0, 0.5, 0.0);
glEnd();
glfwSwapBuffers(window);
glfwPollEvents();
}
glfwTerminate();
return EXIT_SUCCESS;
}
Or supply some shaders & use a VAO & VBO to upload your geometry.

Why don't I need to load shaders when using GLFW?

According to a book I'm reading, vertex and fragment shaders are required for the newest versions of OpenGL, and if they're not provided, rendering will not happen properly.
I'm using the GLFW library (3.0.4), and in the spinning triangle Hello World type example, there is no code to load the GPU with these shaders. I cannot find anything that says whether GLFW provides default shaders or not...
Below is the example code I'm referring to. There are calls to glColor3f(), which might be involved.
Also, I notice that the OpenGL.org documentation doesn't seem to list glColor*() at all! Why is this?
#include "GLFW\glfw3.h"
static void error_callback(int error, const char* description)
{
fputs(description, stderr);
}
static void key_callback(GLFWwindow* window, int key, int scancode, int action, int mods)
{
if (key == GLFW_KEY_ESCAPE && action == GLFW_PRESS)
glfwSetWindowShouldClose(window, GL_TRUE);
}
int main(void)
{
GLFWwindow* window;
glfwSetErrorCallback(error_callback);
if (!glfwInit())
exit(EXIT_FAILURE);
window = glfwCreateWindow(640, 480, "Simple example", NULL, NULL);
if (!window)
{
glfwTerminate();
exit(EXIT_FAILURE);
}
glfwMakeContextCurrent(window);
glfwSetKeyCallback(window, key_callback);
while (!glfwWindowShouldClose(window))
{
float ratio;
int width, height;
glfwGetFramebufferSize(window, &width, &height);
ratio = width / (float)height;
glViewport(0, 0, width, height);
glClear(GL_COLOR_BUFFER_BIT);
glMatrixMode(GL_PROJECTION);
glLoadIdentity();
glOrtho(-ratio, ratio, -1.f, 1.f, 1.f, -1.f);
glMatrixMode(GL_MODELVIEW);
glLoadIdentity();
glRotatef((float)glfwGetTime() * 50.f, 0.f, 0.f, 1.f);
glBegin(GL_TRIANGLES);
glColor3f(1.f, 0.f, 0.f);
glVertex3f(-0.6f, -0.4f, 0.f);
glColor3f(0.f, 1.f, 0.f);
glVertex3f(0.6f, -0.4f, 0.f);
glColor3f(0.f, 0.f, 1.f);
glVertex3f(0.f, 0.6f, 0.f);
glEnd();
glfwSwapBuffers(window);
glfwPollEvents();
}
glfwDestroyWindow(window);
glfwTerminate();
exit(EXIT_SUCCESS);
}
glBegin and glEnd indicate you use immediate mode aka the fixed function pipeline which predates shaders. That pipeline is also outdated and removed from 4.0+ core profiles.