glFrustum on Macbook Pro gives unexpected results - opengl

Question

I'm just setting up a simple renderer using LWJGL 3 and when it runs on my external display it looks like I expect but when resize it on my Macbook it shrinks the viewport. Then if I move the window it fixes it. Here's the code that I run when I init my GL stuff and on window resize.
public void resize(int width, int height)
{
val near = 0.1
val far = 100.0
GL11.glViewport(0, 0, width, height);
GL11.glMatrixMode(GL11.GL_PROJECTION);
GL11.glLoadIdentity();
float aspect = width / (float)height
float fov = (float)(45.0 / 360.0 * Math.PI)
float fH = Math.tan(fov) * near
float fW = fH * aspect
GL11.glFrustum(-fW, fW, -fH, fH, near, far);
GL11.glMatrixMode(GL11.GL_MODELVIEW);
GL11.glLoadIdentity();
}
Here's what I'm seeing
Wrong
Right
If I'm running it on my external display it doesn't change, it's always right.

Answer 1

Reading the size of the frame buffer was the answer here. I create the window with the pixel size the user passes in and then read the frameBuffer size to pass to glViewport.
public Window(String title, int width, int height)
{
_errorCallback = GLFWErrorCallback.createPrint(System.err);
GLFW.glfwSetErrorCallback(_errorCallback);
if (GLFW.glfwInit() != GLFW.GLFW_TRUE)
{
throw IllegalStateException("Unable to initialize GLFW");
}
GLFW.glfwDefaultWindowHints();
GLFW.glfwWindowHint(GLFW.GLFW_VISIBLE, GLFW.GLFW_FALSE);
GLFW.glfwWindowHint(GLFW.GLFW_RESIZABLE, GLFW.GLFW_TRUE);
_window = GLFW.glfwCreateWindow(width, height, title ?: "", 0, 0);
if (_window == 0L)
{
throw RuntimeException("Failed to create window");
}
// Setup Callbacks
// Get the resolution of the primary monitor
GLFWVidMode vidmode = GLFW.glfwGetVideoMode(GLFW.glfwGetPrimaryMonitor());
// Center our window
GLFW.glfwSetWindowPos(_window, (vidmode.width() - width) / 2, (vidmode.height() - height) / 2);
// Make the OpenGL context current
GLFW.glfwMakeContextCurrent(_window);
// Enable v-sync
GLFW.glfwSwapInterval(1);
// Make the window visible
GLFW.glfwShowWindow(_window);
}
Then I read the frame buffer size to pass into glViewport and glFrustum.
public Vector2 frameBufferSize()
{
IntBuffer bufferWidth = BufferUtils.createIntBuffer(4);
IntBuffer bufferHeight = BufferUtils.createIntBuffer(4);
GLFW.glfwGetFramebufferSize(_window, bufferWidth, bufferHeight);
return Vector2(bufferWidth.get(0), bufferHeight.get(0));
}