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jccourtney

OpenGL OpenGL and user defined functions/classes with c++ issues

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jccourtney    115

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?

Edited by jccourtney

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Brother Bob    10344

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.

Edited by Brother Bob

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jccourtney    115

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"; }
}
Edited by jccourtney

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larspensjo    1561

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.

 

Sorry, I don't have a specific answer to your question. You have the experienced the black screen of death in OpenGL. There are quite a lot of single point of failures when programming OpenGL, and many of them will give you a black screen.

 

My personal experience is to do as follows:

  1. Whenever something works, I check it in to a version control.
  2. I make many small check ins, making it easy to back step when something stops working.
  3. I make sure every small step still works.

This relates not only to OpenGL, of course. Now and then, I grow more confident as I feel I have enough experience. And then I suddenly have to spend a lot of time debugging and try to understand why something was broken.

 

Otherwise, I would say you are on the right path. That is, you need to create a library/framework for using OpenGL (or use a library from someone else). OpenGL is low level programming, and it has helped me to add some layers above it.

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Brother Bob    10344

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.

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jccourtney    115

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"; }
}

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shacktar    1512
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.

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jccourtney    115

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.

Edited by jccourtney

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jccourtney    115

 

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!

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      hi all,

      i am trying to build an OpenGL 2D GUI system, (yeah yeah, i know i should not be re inventing the wheel, but this is for educational and some other purpose only),
      i have built GUI system before using 2D systems such as that of HTML/JS canvas, but in 2D system, i can directly match a mouse coordinates to the actual graphic coordinates with additional computation for screen size/ratio/scale ofcourse.
      now i want to port it to OpenGL, i know that to render a 2D object in OpenGL we specify coordiantes in Clip space or use the orthographic projection, now heres what i need help about.
      1. what is the right way of rendering the GUI? is it thru drawing in clip space or switching to ortho projection?
      2. from screen coordinates (top left is 0,0 nd bottom right is width height), how can i map the mouse coordinates to OpenGL 2D so that mouse events such as button click works? In consideration ofcourse to the current screen/size dimension.
      3. when let say if the screen size/dimension is different, how to handle this? in my previous javascript 2D engine using canvas, i just have my working coordinates and then just perform the bitblk or copying my working canvas to screen canvas and scale the mouse coordinates from there, in OpenGL how to work on a multiple screen sizes (more like an OpenGL ES question).
      lastly, if you guys know any books, resources, links or tutorials that handle or discuss this, i found one with marekknows opengl game engine website but its not free,
      Just let me know. Did not have any luck finding resource in google for writing our own OpenGL GUI framework.
      IF there are no any available online, just let me know, what things do i need to look into for OpenGL and i will study them one by one to make it work.
      thank you, and looking forward to positive replies.
    • By fllwr0491
      I have a few beginner questions about tesselation that I really have no clue.
      The opengl wiki doesn't seem to talk anything about the details.
       
      What is the relationship between TCS layout out and TES layout in?
      How does the tesselator know how control points are organized?
          e.g. If TES input requests triangles, but TCS can output N vertices.
             What happens in this case?
      In this article,
      http://www.informit.com/articles/article.aspx?p=2120983
      the isoline example TCS out=4, but TES in=isoline.
      And gl_TessCoord is only a single one.
      So which ones are the control points?
      How are tesselator building primitives?
    • By Orella
      I've been developing a 2D Engine using SFML + ImGui.
      Here you can see an image
      The editor is rendered using ImGui and the scene window is a sf::RenderTexture where I draw the GameObjects and then is converted to ImGui::Image to render it in the editor.
      Now I need to create a 3D Engine during this year in my Bachelor Degree but using SDL2 + ImGui and I want to recreate what I did with the 2D Engine. 
      I've managed to render the editor like I did in the 2D Engine using this example that comes with ImGui. 
      3D Editor preview
      But I don't know how to create an equivalent of sf::RenderTexture in SDL2, so I can draw the 3D scene there and convert it to ImGui::Image to show it in the editor.
      If you can provide code will be better. And if you want me to provide any specific code tell me.
      Thanks!
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