Why can't I have a thread render while resources are loaded

OpenGL OpenGL: Basic Coding
1

I want something to show up in the window while my resources are loading.

So this is what I have in my thread:

#pragma once

#define GLEW_STATIC
#include "GL/glew.h"
#include "GLFW/glfw3.h"

#include "ShaderProgram.h"
#include "Texture2D.h"

namespace Alt {
	bool RenContinue = true;

	GLFWwindow* AltWindow = NULL;

	ShaderProgram passShad;

	void renLoop() {
		
		float theLine = 0;		

		Texture2D capTex;
		capTex.loadTexture("Textures/caption.png");

		GLfloat scrnVertices[] = {
			// position			 // tex coords
			-1.0f,  1.0f, 0.0f,	 0.0f, 1.0f,		// Top left
			 1.0f,  1.0f, 0.0f,	 1.0f, 1.0f,		// Top right
			 1.0f, -1.0f, 0.0f,	 1.0f, 0.0f,		// Bottom right
			-1.0f, -1.0f, 0.0f,	 0.0f, 0.0f			// Bottom left 
		};

		GLuint scrnIndices[] = {
			0, 3, 2,  // First Triangle
			0, 2, 1   // Second Triangle
		};

		GLuint svbo, sibo, svao;

		glGenBuffers(1, &svbo);					// Generate an empty vertex buffer on the GPU
		glBindBuffer(GL_ARRAY_BUFFER, svbo);		// "bind" or set as the current buffer we are working with
		glBufferData(GL_ARRAY_BUFFER, sizeof(scrnVertices), scrnVertices, GL_STATIC_DRAW);	// copy the data from CPU to GPU

		glGenVertexArrays(1, &svao);				// Tell OpenGL to create new Vertex Array Object
		glBindVertexArray(svao);					// Make it the current one

		// Position attribute
		glVertexAttribPointer(0, 3, GL_FLOAT, GL_FALSE, 5 * sizeof(GLfloat), (GLvoid*)(0));
		glEnableVertexAttribArray(0);

		// Texture Coord attribute
		glVertexAttribPointer(1, 2, GL_FLOAT, GL_FALSE, 5 * sizeof(GLfloat), (GLvoid*)(3 * sizeof(GLfloat)));
		glEnableVertexAttribArray(1);

		// Set up index buffer
		glGenBuffers(1, &sibo);	// Create buffer space on the GPU for the index buffer
		glBindBuffer(GL_ELEMENT_ARRAY_BUFFER, sibo);
		glBufferData(GL_ELEMENT_ARRAY_BUFFER, sizeof(scrnIndices), scrnIndices, GL_STATIC_DRAW);

		glBindVertexArray(0);

		glClearColor(.5, .5, 1, 1);

		double deltaTime;
		double lastTime = glfwGetTime();

		while (RenContinue && !glfwWindowShouldClose(AltWindow)) {
			glfwPollEvents();
			glClear(GL_COLOR_BUFFER_BIT | GL_DEPTH_BUFFER_BIT);
			double currentTime = glfwGetTime();
			deltaTime = currentTime - lastTime;
			lastTime = currentTime;

			passShad.use();
			passShad.setUniformSampler("texSampler1", 0);
			passShad.setUniform("lineStart", theLine);
			capTex.bind(0);
			glBindVertexArray(svao);
			glDrawElements(GL_TRIANGLES, 6, GL_UNSIGNED_INT, 0);
			glBindVertexArray(0);
			capTex.unbind(0);
			theLine += deltaTime * .25;
			if (theLine > 1) theLine = 0;

			glfwSwapBuffers(AltWindow);
		}
	}
}

The ‘AltWindow’ has been loaded from my main thread and is defined. All I see is a black window.