I'm currently learning modern OpenGL. So far I have been programming everything within the same scope of the primary cpp file, but the more I learn, the more that file becomes very lengthy and cluttered. So naturally, I have been trying to break up my code by putting some within a user defined function and even a user defined class, but I keep having the same problem in that I just have a black screen instead of a rendered triangle.

I am currently using Glfw3 and Glew with my code if that helps. I have also tried passing certain values, like window handles, but to no avail. If I put all the code within my user defined function in main(), the triangle becomes rendered.

Here is my code:

framework.h

#include <GL/glew.h>
#include <GLFW/glfw3.h>
#include <iostream>
#include <fstream>

#pragma comment(lib, "glfw3dll.lib")
#pragma comment(lib, "glew32.lib")
#pragma comment(lib, "opengl32.lib")

using namespace std;

framework.cpp

#include "framework.h"
#include "rendering.h"


int windowWidth = 800;
int windowHeight = 450;
ofstream outFile("output.txt");
renderingUtils renderingClass; //Rendering Utils Class
void renderFunction(float*, GLFWwindow*);

float triangleW = 0.125;
float triangleH = 0.125;
float coordinateX = 0.25;
float coordinateY = 0.25;
float points[24] = {
	0.0f, 0.0f, 0.0f, 1.0f,
	0.5f, 0.0f, 0.0f, 1.0f,
	0.0f, 0.5f, 0.0f, 1.0f,
	1.0f, 0.0f, 0.0f, 1.0f,
	0.0f, 1.0f, 0.0f, 1.0f,
	0.0f, 0.0f, 1.0f, 1.0f,
};
/*float points[24] = {  //Vertex Information
	coordinateX, coordinateY, 0.0f, 1.0f,
	coordinateX + triangleW, coordinateY, 0.0f, 1.0f,
	coordinateX + (triangleW / 2), coordinateY + triangleH, 0.0f, 1.0f, //First Triangle
	1.0f, 0.0f, 0.0f, 1.0f,
	0.0f, 1.0f, 0.0f, 1.0f,
	0.0f, 0.0f, 1.0f, 1.0f, //Color Information
};*/

int main(){

	//Start GL context O/S window using the GLFW helper library
	if (!glfwInit()){
		outFile << "ERROR: Could not start GLFW3\n";
		return 1;
	}

	GLFWwindow* window = glfwCreateWindow(windowWidth, windowHeight, "Tutorial Project", NULL, NULL);
	if (!window){
		outFile << "ERROR: Could not open window with GLFW3\n";
		glfwTerminate();
		return 1;
	}

	glfwMakeContextCurrent(window);

	//start GLEW extension handler
	glewExperimental = GL_TRUE;
	glewInit();

	//Get version info
	const GLubyte* renderer = glGetString(GL_RENDERER); //Get renderer string
	const GLubyte* version = glGetString(GL_VERSION); //Version as a string

	std::cout << "Renderer: " << renderer << "\n";
	std::cout << "OpenGL version supported: " << version << "\n";



	//Initialize Display
	renderFunction(points, window);



	
	while (!glfwWindowShouldClose(window)){
		//Compute Position Offsets
		//Adjust Vertex Data
		//Render Display
		//renderingClass.updateScene();





		//Update other events like input handling
		glfwPollEvents();

	}
	
	//Close GL context and any other GLFW resources
	glfwTerminate();
	getchar();
	return 0;

}

void renderFunction(float* points, GLFWwindow* window){
	glfwMakeContextCurrent(window);

	// Test Code below
	unsigned int vbo = 0;
	unsigned int vao = 0;
	unsigned int vs;
	unsigned int fs;
	unsigned int program;
	const char* vertex_shader =
		"#version 330\n"
		"layout(location = 0) in vec4 position;"
		"layout(location = 1) in vec4 color;"
		"smooth out vec4 theColor;"
		"void main () {"
		"  gl_Position = position;"
		"  theColor = color;"
		"}";
	const char* fragment_shader =
		"#version 330\n"
		"smooth in vec4 theColor;"
		"out vec4 outputColor;"
		"void main () {"
		"  outputColor = theColor;"
		"}";
	std::cout << "Scene set up.\n";
	std::cout << points[4] << "\n";
	//Tell GL to only draw onto a pixel if the shape is closer to the viewer
	glEnable(GL_DEPTH_TEST); //Enable Depth-Testing
	glDepthFunc(GL_LESS); //Depth-testing interprests a smaller value as "closer"
	glViewport(0, 0, (GLsizei)800, (GLsizei)450);

	glGenBuffers(1, &vbo); //
	glBindBuffer(GL_ARRAY_BUFFER, vbo); //
	glBufferData(GL_ARRAY_BUFFER, sizeof(points), points, GL_STATIC_DRAW); //
	glBindBuffer(GL_ARRAY_BUFFER, 0);

	glGenVertexArrays(1, &vao); //
	glBindVertexArray(vao); //
	glBindBuffer(GL_ARRAY_BUFFER, vbo);
	glEnableVertexAttribArray(0); //
	glEnableVertexAttribArray(1); //

	glVertexAttribPointer(0, 4, GL_FLOAT, GL_FALSE, 0, 0); //
	glVertexAttribPointer(1, 4, GL_FLOAT, GL_FALSE, 0, (void*)48); //


	vs = glCreateShader(GL_VERTEX_SHADER);//
	glShaderSource(vs, 1, &vertex_shader, NULL); //
	glCompileShader(vs); //

	GLint status;
	glGetShaderiv(vs, GL_COMPILE_STATUS, &status);
	if (status == GL_FALSE) { std::cout << "Compile status1: fail\n"; }
	fs = glCreateShader(GL_FRAGMENT_SHADER); //
	glShaderSource(fs, 1, &fragment_shader, NULL); //
	glCompileShader(fs); //
	GLint status2;
	glGetShaderiv(fs, GL_COMPILE_STATUS, &status2);
	if (status2 == GL_FALSE){ std::cout << "Compile status2: fail\n"; }

	program = glCreateProgram(); //
	glAttachShader(program, fs); //
	glAttachShader(program, vs); //
	glLinkProgram(program); //
	GLint status3;
	glGetProgramiv(program, GL_LINK_STATUS, &status3);
	if (status3 == GL_FALSE) { std::cout << "GL program failure \n"; }

	glClearColor(0.0f, 0.0f, 0.0f, 0.0f); //
	glClear(GL_COLOR_BUFFER_BIT | GL_DEPTH_BUFFER_BIT); //

	glUseProgram(program); //
	glBindVertexArray(vao); //
	glDrawArrays(GL_TRIANGLES, 0, 3); //

	glfwSwapBuffers(window);
}

Any ideas as why this is not working?

Oe problem, at least, is your glBufferData call where you use sizeof(points). The variable points is a pointer, thus sizeof(points) is the size of the pointer. You are thus loading a buffer with, most likely, either 4 of 8 bytes of data. If you want the size of the original points array that you pass to renderFunction, you need to pass its size to the function, because once the array decays into the pointer at the call site, the size information is lost.

But, that aside, do not create and upload data in a render function. Make it a separate init function, and have the render function refer to the buffer objects instead.

Brother Bob,

I corrected that and also adjust my code to your suggestion, but unfortunately I'm still just getting a black screen.

Here's my updated framework.cpp file:

#include "framework.h"

int windowWidth = 800;
int windowHeight = 450;
ofstream outFile("output.txt");
void renderFunction(float*, GLFWwindow*, GLuint*, GLuint*, GLuint*, GLuint*, GLuint*);
void initRenderer(float*, GLFWwindow*, GLuint*, GLuint*, GLuint*, GLuint*, GLuint*);
float triangleW = 0.125;
float triangleH = 0.125;
float coordinateX = 0.25;
float coordinateY = 0.25;
float points[24] = {
	0.0f, 0.0f, 0.0f, 1.0f,
	0.5f, 0.0f, 0.0f, 1.0f,
	0.0f, 0.5f, 0.0f, 1.0f,
	1.0f, 0.0f, 0.0f, 1.0f,
	0.0f, 1.0f, 0.0f, 1.0f,
	0.0f, 0.0f, 1.0f, 1.0f,
};
GLuint vbo = 0;
GLuint vao = 0;
GLuint vs;
GLuint fs;
GLuint program;

int main(){

	//Start GL context O/S window using the GLFW helper library
	if (!glfwInit()){
		outFile << "ERROR: Could not start GLFW3\n";
		return 1;
	}

	GLFWwindow* window = glfwCreateWindow(windowWidth, windowHeight, "Tutorial Project", NULL, NULL);
	if (!window){
		outFile << "ERROR: Could not open window with GLFW3\n";
		glfwTerminate();
		return 1;
	}
	
	glfwMakeContextCurrent(window);

	//start GLEW extension handler
	glewExperimental = GL_TRUE;
	glewInit();

	//Get version info
	const GLubyte* renderer = glGetString(GL_RENDERER); //Get renderer string
	const GLubyte* version = glGetString(GL_VERSION); //Version as a string

	std::cout << "Renderer: " << renderer << "\n";
	std::cout << "OpenGL version supported: " << version << "\n";



	//Initialize Display
	initRenderer(points, window, &vbo, &vao, &vs, &fs, &program);



	
	while (!glfwWindowShouldClose(window)){
		//Compute Position Offsets
		//Adjust Vertex Data
		//Render Display
		//renderingClass.updateScene();
		renderFunction(points, window, &vbo, &vao, &vs, &fs, &program);




		//Update other events like input handling
		glfwPollEvents();

	}
	
	//Close GL context and any other GLFW resources
	glfwTerminate();
	getchar();
	return 0;

}

void renderFunction(float* points, GLFWwindow* window, GLuint* vbo, GLuint* vao, GLuint* vs, GLuint* fs, GLuint* program){
	glfwMakeContextCurrent(window);
	glClearColor(0.0f, 0.0f, 0.0f, 0.0f);
	glClear(GL_COLOR_BUFFER_BIT);
	glUseProgram(*program);
	glBindBuffer(GL_ARRAY_BUFFER, *vbo);
	glEnableVertexAttribArray(0);
	glVertexAttribPointer(0, 4, GL_FLOAT, GL_FALSE, 0, 0);
	glVertexAttribPointer(1, 4, GL_FLOAT, GL_FALSE, 0, (void*)48);

	glDrawArrays(GL_TRIANGLES, 0, 3);

	glDisableVertexAttribArray(0);
	glUseProgram(0);

	glfwSwapBuffers(window);

}

void initRenderer(float* points, GLFWwindow* window, GLuint* vbo, GLuint* vao, GLuint* vs, GLuint* fs, GLuint* program){
	glfwMakeContextCurrent(window);
	const char* vertex_shader =
		"#version 330\n"
		"layout(location = 0) in vec4 position;"
		"layout(location = 1) in vec4 color;"
		"smooth out vec4 theColor;"
		"void main () {"
		"  gl_Position = position;"
		"  theColor = color;"
		//vec4 (vp, 1.0);"
		"}";
	const char* fragment_shader =
		"#version 330\n"
		"smooth in vec4 theColor;"
		"out vec4 outputColor;"
		"void main () {"
		"  outputColor = theColor;"
		"}";

	//Tell GL to only draw onto a pixel if the shape is closer to the viewer
	glEnable(GL_DEPTH_TEST); //Enable Depth-Testing
	glDepthFunc(GL_LESS); //Depth-testing interprests a smaller value as "closer"
	glViewport(0, 0, (GLsizei)800, (GLsizei)450);

	glGenBuffers(1, vbo); 
	glBindBuffer(GL_ARRAY_BUFFER, *vbo); 
	glBufferData(GL_ARRAY_BUFFER, sizeof(points), points, GL_STATIC_DRAW); //
	glBindBuffer(GL_ARRAY_BUFFER, 0);

	glGenVertexArrays(1, vao);
	glBindVertexArray(*vao);
	glBindBuffer(GL_ARRAY_BUFFER, *vbo);
	glEnableVertexAttribArray(0); 
	glEnableVertexAttribArray(1); 

	glVertexAttribPointer(0, 4, GL_FLOAT, GL_FALSE, 0, 0); 
	glVertexAttribPointer(1, 4, GL_FLOAT, GL_FALSE, 0, (void*)48); 


	*vs = glCreateShader(GL_VERTEX_SHADER);
	glShaderSource(*vs, 1, &vertex_shader, NULL); 
	glCompileShader(*vs); //

	GLint status;
	glGetShaderiv(*vs, GL_COMPILE_STATUS, &status);
	if (status == GL_FALSE) { std::cout << "Compile status1: fail\n"; }
	*fs = glCreateShader(GL_FRAGMENT_SHADER); //
	glShaderSource(*fs, 1, &fragment_shader, NULL); //
	glCompileShader(*fs); //
	
	GLint status2;
	glGetShaderiv(*fs, GL_COMPILE_STATUS, &status2);
	if (status2 == GL_FALSE){ std::cout << "Compile status2: fail\n"; }

	*program = glCreateProgram(); //
	glAttachShader(*program, *fs); //
	glAttachShader(*program, *vs); //
	glLinkProgram(*program); //
	GLint status3;
	glGetProgramiv(*program, GL_LINK_STATUS, &status3);
	if (status3 == GL_FALSE) { std::cout << "GL program failure \n"; }
}

You didn't correct the error I mentioned. In initRenderer, you are still taking the size of the pointer in the call to glBufferData, not the size of the original array data; points is still a pointer, and sizeof(points) still returns the size of the pointer which is likely either 4 or 8 bytes. You need to pass the size of the array data to initRenderer, because it cannot know the size of the original array by the pointer alone.

You didn't correct the error I mentioned. In initRenderer, you are still taking the size of the pointer in the call to glBufferData, not the size of the original array data; points is still a pointer, and sizeof(points) still returns the size of the pointer which is likely either 4 or 8 bytes. You need to pass the size of the array data to initRenderer, because it cannot know the size of the original array by the pointer alone.

Brother Bob, I updated the code to include the hard coded value of the array length and sizeof(float) in the glBufferData call. I also changed the prototype and declaration sections to use float points[] instead of float* points.

#include "framework.h"

int windowWidth = 800;
int windowHeight = 450;
ofstream outFile("output.txt");
void renderFunction(float[], GLFWwindow*, GLuint*, GLuint*, GLuint*, GLuint*, GLuint*);
void initRenderer(float[], GLFWwindow*, GLuint*, GLuint*, GLuint*, GLuint*, GLuint*);
float triangleW = 0.125;
float triangleH = 0.125;
float coordinateX = 0.25;
float coordinateY = 0.25;
float points[24] = {
	0.0f, 0.0f, 0.0f, 1.0f,
	0.5f, 0.0f, 0.0f, 1.0f,
	0.0f, 0.5f, 0.0f, 1.0f,
	1.0f, 0.0f, 0.0f, 1.0f,
	0.0f, 1.0f, 0.0f, 1.0f,
	0.0f, 0.0f, 1.0f, 1.0f,
};
GLuint vbo = 0;
GLuint vao = 0;
GLuint vs;
GLuint fs;
GLuint program;



/*float points[24] = {  //Vertex Information
	coordinateX, coordinateY, 0.0f, 1.0f,
	coordinateX + triangleW, coordinateY, 0.0f, 1.0f,
	coordinateX + (triangleW / 2), coordinateY + triangleH, 0.0f, 1.0f, //First Triangle
	1.0f, 0.0f, 0.0f, 1.0f,
	0.0f, 1.0f, 0.0f, 1.0f,
	0.0f, 0.0f, 1.0f, 1.0f, //Color Information
};*/

int main(){
	//Start GL context O/S window using the GLFW helper library
	if (!glfwInit()){
		outFile << "ERROR: Could not start GLFW3\n";
		return 1;
	}

	GLFWwindow* window = glfwCreateWindow(windowWidth, windowHeight, "Tutorial Project", NULL, NULL);
	if (!window){
		outFile << "ERROR: Could not open window with GLFW3\n";
		glfwTerminate();
		return 1;
	}
	
	glfwMakeContextCurrent(window);

	//start GLEW extension handler
	glewExperimental = GL_TRUE;
	glewInit();

	//Get version info
	const GLubyte* renderer = glGetString(GL_RENDERER); //Get renderer string
	const GLubyte* version = glGetString(GL_VERSION); //Version as a string

	std::cout << "Renderer: " << renderer << "\n";
	std::cout << "OpenGL version supported: " << version << "\n";



	//Initialize Display
	initRenderer(points, window, &vbo, &vao, &vs, &fs, &program);



	
	while (!glfwWindowShouldClose(window)){

		renderFunction(points, window, &vbo, &vao, &vs, &fs, &program);




		//Update other events like input handling
		glfwPollEvents();

	}
	
	//Close GL context and any other GLFW resources
	glfwTerminate();
	getchar();
	return 0;

}

void renderFunction(float points[], GLFWwindow* window, GLuint* vbo, GLuint* vao, GLuint* vs, GLuint* fs, GLuint* program){
	glfwMakeContextCurrent(window);
	glClearColor(0.0f, 0.0f, 0.3f, 0.0f);
	glClear(GL_COLOR_BUFFER_BIT);
	glUseProgram(*program);
	glBindBuffer(GL_ARRAY_BUFFER, *vbo);
	glEnableVertexAttribArray(0);
	glVertexAttribPointer(0, 4, GL_FLOAT, GL_FALSE, 0, 0);
	glVertexAttribPointer(1, 4, GL_FLOAT, GL_FALSE, 0, (void*)48);

	glDrawArrays(GL_TRIANGLES, 0, 3);

	glDisableVertexAttribArray(0);
	glUseProgram(0);

	glfwSwapBuffers(window);

}

void initRenderer(float points[], GLFWwindow* window, GLuint* vbo, GLuint* vao, GLuint* vs, GLuint* fs, GLuint* program){
	glfwMakeContextCurrent(window);
	const char* vertex_shader =
		"#version 330\n"
		"layout(location = 0) in vec4 position;"
		"layout(location = 1) in vec4 color;"
		"smooth out vec4 theColor;"
		"void main () {"
		"  gl_Position = position;"
		"  theColor = color;"
		"}";
	const char* fragment_shader =
		"#version 330\n"
		"smooth in vec4 theColor;"
		"out vec4 outputColor;"
		"void main () {"
		"  outputColor = theColor;"
		"}";

	//Tell GL to only draw onto a pixel if the shape is closer to the viewer
	glEnable(GL_DEPTH_TEST); //Enable Depth-Testing
	glDepthFunc(GL_LESS); //Depth-testing interprests a smaller value as "closer"
	glViewport(0, 0, (GLsizei)800, (GLsizei)450);

	glGenBuffers(1, vbo); 
	glBindBuffer(GL_ARRAY_BUFFER, *vbo); 
	glBufferData(GL_ARRAY_BUFFER, 24*sizeof(float), points, GL_STATIC_DRAW); //
	glBindBuffer(GL_ARRAY_BUFFER, 0);


	glGenVertexArrays(1, vao);
	glBindVertexArray(*vao);
	glBindBuffer(GL_ARRAY_BUFFER, *vao);
	glEnableVertexAttribArray(0); 
	glEnableVertexAttribArray(1); 

	glVertexAttribPointer(0, 4, GL_FLOAT, GL_FALSE, 0, 0); 
	glVertexAttribPointer(1, 4, GL_FLOAT, GL_FALSE, 0, (void*)48); 


	*vs = glCreateShader(GL_VERTEX_SHADER);
	glShaderSource(*vs, 1, &vertex_shader, NULL); 
	glCompileShader(*vs); //

	GLint status;
	glGetShaderiv(*vs, GL_COMPILE_STATUS, &status);
	if (status == GL_FALSE) { std::cout << "Compile status1: fail\n"; }
	*fs = glCreateShader(GL_FRAGMENT_SHADER); //
	glShaderSource(*fs, 1, &fragment_shader, NULL); //
	glCompileShader(*fs); //
	
	GLint status2;
	glGetShaderiv(*fs, GL_COMPILE_STATUS, &status2);
	if (status2 == GL_FALSE){ std::cout << "Compile status2: fail\n"; }

	*program = glCreateProgram(); //
	glAttachShader(*program, *fs); //
	glAttachShader(*program, *vs); //
	glLinkProgram(*program); //
	GLint status3;
	glGetProgramiv(*program, GL_LINK_STATUS, &status3);
	if (status3 == GL_FALSE) { std::cout << "GL program failure \n"; }
}

glBindBuffer(GL_ARRAY_BUFFER, *vao);

Here, in initRenderer (line 144) you're attempting to bind a VAO as a VBO. Try using *vbo there.

In your renderFunction it looks like you're rendering with the VBO but your VAO is still bound. Pick one or the other. If you want to render with the VBO directly (and this is preferred to VAOs anyway), then disable your VAO before calling your renderFunction.

Your clear color is also fully transparent. You probably want a 1.0f as the last component.

Using the above code, I found that by simply deleting the lines below or even changing the second line to GL_ALWAYS, I managed to produce a rendered triangle.

	glEnable(GL_DEPTH_TEST); //Enable Depth-Testing
	glDepthFunc(GL_LESS); //Depth-testing interprets a smaller value as "closer" 

Now the question is why? I checked my vertex data, which is the first half of the array points, and I used a z value of 0. Does anyone have any ideas?

UPDATE:

I changed line 96, while not implementing my findings as above, from

glClear(GL_COLOR_BUFFER_BIT);

to

glClear(GL_COLOR_BUFFER_BIT | GL_DEPTH_BUFFER_BIT);

and I was able to get a rendered triangle.

glBindBuffer(GL_ARRAY_BUFFER, *vao);

Here, in initRenderer (line 144) you're attempting to bind a VAO as a VBO. Try using *vbo there.

In your renderFunction it looks like you're rendering with the VBO but your VAO is still bound. Pick one or the other. If you want to render with the VBO directly (and this is preferred to VAOs anyway), then disable your VAO before calling your renderFunction.

Your clear color is also fully transparent. You probably want a 1.0f as the last component.

Thanks! I'll go ahead and make those two changes with the glClearColor call and line 144. Can you explain a little more what you mean by rendering with the VBO directly? I've tried looking online for some more information, but so far I haven't found anything useful that doesn't include VAOs.

My basic understanding for rendering (the loop, not the initial setup) is, assuming a static draw, the following:

...
glBindVertexArray(vertexArrayObject);
glBindBuffer(GL_ARRAY_BUFFER, vertexBufferObject1);

glEnableVertexAttribArray(0);


glBindBuffer(GL_ARRAY_BUFFER, vertexBufferObjectN); //Any remaining vbos that might contain color information, etc
glEnableVertexAttribArray(N); //For any additional indexes, such as if there were an additional one for color, etc
glVertexAttribPointer(N, 4, GL_FLOAT, GL_FALSE, 0, 0); //For any additional indexes and buffers

glUseProgram(program);
glDrawArrays(GL_TRIANGLES, 0, 3);

//Clean up functions to follow

Is anything incorrect or redundant here? Thanks!