OpenGL Rendering Constricted to bottom left quarter of the screen

Question

So I'm working on an OpenGL project in C++ and I'm running into a weird issue where after creating the GLFWwindow and drawing to it, the area that I'm drawing in only encompasses the bottom left quarter of the screen. For example if the screen dimensions are 640x480, and I drew a 40x40 square at (600, 440) it shows up here, instead of in the top right corner like I would expect:

If I move the square into an area that's not within the 640x480 parameter it gets cut off, like below:

I'll post my code from main.cpp below:

#define FRAME_CAP 5000.0;

#include <iostream>
#include <GL/glew.h>
#include <GLFW/glfw3.h>
#include "InputHandler.h"
#include "Game.h"
using namespace std;

void gameLoop(GLFWwindow *window){
    InputHandler input = InputHandler(window);

    Game game = Game(input);

    //double frameTime = 1.0 / FRAME_CAP;

    while(!glfwWindowShouldClose(window)){
        GLint windowWidth, windowHeight;
        glfwGetWindowSize(window, &windowWidth, &windowHeight);
        glMatrixMode(GL_PROJECTION);
        glLoadIdentity();
        glOrtho(0.0, windowWidth, 0.0, windowHeight, -1.0, 1.0);
        glMatrixMode(GL_MODELVIEW);
        glLoadIdentity();
        glViewport(0, 0, windowWidth, windowHeight);

        game.render();
        game.handleInput();
        game.update();

        glfwSwapBuffers(window);
        glfwPollEvents();

    }

}

int main(int argc, const char * argv[]){
    GLFWwindow *window;

    if(!glfwInit()){
        return -1;
    }

    window = glfwCreateWindow(640.0, 480.0, "OpenGL Base Project", NULL, NULL);

    if(!window){
        glfwTerminate();
        exit(EXIT_FAILURE);
    }

    glewInit();

    glfwMakeContextCurrent(window);

    gameLoop(window);

    glfwTerminate();
    exit(EXIT_SUCCESS);
}

I'm not sure why this would be happening, but if you have any ideas let me know, thank you!

Amalee

Make sure you are not running into issues where window size is not equal to the framebuffer size. – Temuco

I have the same issue on my mac, opengl 4.1, it randomly happened, you found a solution? – Signorelli

Answer 1

For those of you like me who bump into this problem, you need to pass the frame buffer size to your glViewport call, like this:

GLFWwindow * window = Application::getInstance().currentWindow;
glfwGetFramebufferSize(window, &frameBufferWidth, &frameBufferHeight);
glViewport(0, 0, frameBufferWidth, frameBufferHeight);

In some devices (mainly Apple Retina displays), the pixel dimensions don't necessarily match your viewport dimensions 1:1. Check here for GLFW documentation.

Signorelli

Answer 2

While Rafael's answer works, another approach you can take is simply to turn off the full resolution framebuffers on Retina displays:

glfwWindowHint(GLFW_COCOA_RETINA_FRAMEBUFFER, GLFW_FALSE);

(reference: the same doc Rafael linked)

Zaneta

But this is worse, right? Since you get lower framebuffer resolution. – Pediform

You get lower framebuffer resolution. Yes, that's my understanding. That may be worse, or could be better if you don't want to decrease performance on rendering to more pixels. – Zaneta