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Knuckler

OpenGL OpenGL AVI class

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I made an OpenGL AVI player and am sharing it with you guys and gals. This is one of the things that have always seemed elusive to OpenGL programmers; at the least being able to have audio and video in sync. It's based on the nehe playing and loading code. A major downside is that it has a lot of dependencies and requirements.

Its all within the bj namespace.

It uses for libraries:
VFW, vfw32.lib / vfw32.dll Already suppied by windows

FMOD, fmodex_vc.lib If you don't need audio, you can comment out the process_audio and init_fmod functions in the Movie constructor

GLEW, glew32.lib This is for OpenGL. You can replace this with GLEE.h or glext.h. Just make sure there is some OpenGL header that supplies you with the declarations, and that there is already a rendering context created. You also need to have a system capable of using PBOs; basically opengl 2.0

Timer.hpp/cpp - A personal timer class based on the QueryPerformance functions.

NOTE: The audio for the AVI must be in PCM16 format. I'm sorry. AVIStreamRead will not read non-pcm/wma audio. Nor is there any way to supply fmod with .wma formatted audio, that I can see.

Movie class methods

play() - plays video

stop() - stops video

bind_texture() - binds the texture of the current frame being displayed
is_playing() - returns true if movie is playing, false otherwise

update() - updates the texture, and audio system. This needs to be called at the beginning of every cycle.

seek_forward() - fast forwards in increments of seekMilliseconds. seekMilliseconds is the second parameter of the Movie constructor, after the file name. The default is 1000 ms or 1 second.

seek_reverse() - seeks backwards in increments of seekMilliseconds.

seek_to_position() - seeks to a position specified in milliseconds from the start of the video.

mute() - sets volume to 0%

unmute() - sets volume to 100%

Here are the classes
Movie.hpp

#ifndef MOVIE_HPP
#define MOVIE_HPP

#ifdef _MSC_VER // use this to include specific libraries with msvc
#pragma comment(lib, "vfw32.lib")
#pragma comment(lib, "fmodex_vc.lib")
#endif // _MSC_VER

#include <Windows.h>
#include <Vfw.h>
#include <fmod.hpp>
#include <string>
#include <vector>
#include "MyTimer.hpp"

namespace bj
{
enum PLAY_STATE
{
PLAYING,
STOPPED
};

class Movie
{
public:
Movie(const std::string fileName_, DWORD seekInMilliseconds = 1000);
~Movie();
void play(); // start updating the texture and audio
void stop(); // Stop and cycle to beginning
void bind_texture();
bool is_playing()const; // Check play state
void update(); // must be called for every cycle
void seek_forward();
void seek_reverse();
void seek_to_position(DWORD positionInMs);
void mute();
void unmute();

private:
static int movieCount; // For VFW AVI library initialization
PLAY_STATE playState;

// For AVI itself
std::string fileName;
PAVIFILE aviFile;
AVIFILEINFO aviFileInfo;
bool hasAudio; // Has audio and or video
bool hasVideo;

// audio
WAVEFORMATEX waveFormat;
LONG audioBufferSize;
FMOD::System *audioSystem; // audio system
FMOD::Sound *audio;
FMOD::Channel *channel;
PAVISTREAM audioStream;
AVISTREAMINFO audioStreamInfo;
std::vector<char> audioBuffer;
long samplesPerSecond;

// video
unsigned int pbo;
int dataSize;
unsigned int texture; // Assumes opengl context has already been created
double nextFrame;
DWORD currentFrame;
DWORD lastFrame;
PAVISTREAM videoStream;
AVISTREAMINFO videoStreamInfo;
PGETFRAME frameDecompressor;
DWORD width; // width and height of video
DWORD height;
DWORD bytesPerPixel;
double mpf; // length for each frame to be displayed in milliseconds

// For play back
bj::Timer timer;
DWORD seekMilliseconds; // Advance or reverse playback position in milliseconds

void process_avi();
void process_audio();
void init_fmod();
void process_video();
void init_opengl();
void grab_frame();
};
}
#endif





Movie.cpp

#include "Movie.hpp"
#include <stdexcept>
#include <string>
#include <fmod.hpp>
#include <sources/glew.h>

// Initialization of static member
int bj::Movie::movieCount = 0;

using namespace bj;

Movie::Movie(const std::string fileName_, DWORD seekInMilliseconds):
playState(STOPPED),
fileName(fileName_),
aviFile(nullptr),
aviFileInfo(),
hasAudio(false),
hasVideo(false),
waveFormat(),
audioBufferSize(0),
audioSystem(nullptr),
audio(nullptr),
audioStream(nullptr),
audioStreamInfo(),
audioBuffer(),
samplesPerSecond(0),
pbo(0),
dataSize(0),
texture(0),
nextFrame(0),
currentFrame(0),
lastFrame(0),
videoStream(nullptr),
videoStreamInfo(),
frameDecompressor(nullptr),
width(0),
height(0),
bytesPerPixel(0),
mpf(0.0),
seekMilliseconds(seekInMilliseconds)
{
// Increment the movieCount. If movieCount == 1, this is the first time it's been initialized
// for this program. Initialize the AVI library
movieCount++;

if(1 == movieCount)
AVIFileInit();

process_avi();
process_audio();
init_fmod();
process_video();
init_opengl();
}

Movie::~Movie()
{
if(aviFile)
AVIFileClose(aviFile);

if(audioStream)
AVIStreamRelease(audioStream);

if(videoStream)
AVIStreamRelease(videoStream);

if(frameDecompressor)
AVIStreamGetFrameClose(frameDecompressor);

if(audio)
audio->release();

if(audioSystem)
audioSystem->close();

if(pbo)
glDeleteBuffers(1, &pbo);

if(texture)
glDeleteTextures(1, &texture);

movieCount--;
// If movieCount == 0, we're finished with the library. Deintialize the library
if(0 == movieCount)
AVIFileExit();
}

void Movie::process_avi()
{
HRESULT error = AVIFileOpenA(&aviFile, fileName.c_str(), OF_READ, nullptr);

if(error)
{
if(AVIERR_FILEOPEN == error)
throw(std::logic_error("Could not open file " + fileName));
else
throw(std::logic_error("Problem with opening file"));
}

AVIFileInfo(aviFile, &aviFileInfo, sizeof(aviFileInfo));
}
void Movie::process_audio()
{
// Check if there is a stream
LONGLONG error = AVIFileGetStream(aviFile, &audioStream, streamtypeAUDIO, 0);

if(AVIERR_NODATA == error)
{
// No audio stream in this file
return;
}
else
{
if(0 != error)
{
// Problem loading audio stream
throw(std::logic_error("Problem loading audio stream"));
}
}

// everything went fine getting the stream
AVIStreamInfo(audioStream, &audioStreamInfo, sizeof(AVISTREAMINFO));

samplesPerSecond = audioStreamInfo.dwRate / audioStreamInfo.dwScale;
float lengthInSeconds = (float)audioStreamInfo.dwLength * audioStreamInfo.dwScale /
audioStreamInfo.dwRate;
float bufferSize = lengthInSeconds * samplesPerSecond;

// Read the stream format

error = AVIStreamReadFormat(audioStream, AVIStreamStart(audioStream), nullptr, &audioBufferSize);

if(error)
{
throw(std::runtime_error("Could not read audio stream format"));
}

std::vector<unsigned char> audioChunk;
audioChunk.resize(audioBufferSize);
AVIStreamReadFormat(audioStream, AVIStreamStart(audioStream), &audioChunk.front(), &audioBufferSize);

memcpy(&waveFormat, &audioChunk.front(), audioChunk.size());

// Read the audio data
audioBufferSize = 0;
error = AVIStreamRead(audioStream, AVIStreamStart(audioStream), (LONG)bufferSize, nullptr, 0, &audioBufferSize, nullptr);

if(AVIERR_FILEREAD == error)
{
throw(std::runtime_error("File error"));
}

if(AVIERR_BUFFERTOOSMALL == error)
{
throw(std::runtime_error("Buffer too small"));
}

if(AVIERR_MEMORY == error)
{
throw(std::runtime_error("Not enough memory to complete operation"));
}

if(error)
{
throw(std::runtime_error("Problem reading stream data"));
}

audioBuffer.resize(audioBufferSize, 0);
LONG bytesRead = 0;
LONG samplesRead = 0;
error = AVIStreamRead(audioStream, AVIStreamStart(audioStream), (LONG)bufferSize, &audioBuffer.front(), audioBufferSize, &bytesRead , &samplesRead);

if(error)
{
throw(std::runtime_error("Problem reading stream data"));
}

}

void Movie::init_fmod()
{
// Check to make sure that there is audio
if(audioBuffer.empty())
return; // No audio

FMOD_RESULT result = FMOD_OK;

result = FMOD::System_Create(&audioSystem);

if(FMOD_OK != result)
{
throw(std::runtime_error("Could not create FMOD system"));
}

result = audioSystem->init(1, FMOD_INIT_NORMAL, nullptr);

if(result != FMOD_OK)
{
throw(std::runtime_error("Could not initialize FMOD system"));
}

// For now, PCM 16 is only supported
FMOD_CREATESOUNDEXINFO exinfo;

memset(&exinfo, 0, sizeof(FMOD_CREATESOUNDEXINFO));
exinfo.cbsize = sizeof(FMOD_CREATESOUNDEXINFO);
exinfo.length = audioBufferSize;
exinfo.format = FMOD_SOUND_FORMAT_PCM16; // Must specify for FMOD_OPENRAW
exinfo.defaultfrequency = waveFormat.nSamplesPerSec; // Must specify for FMOD_OPENRAW
exinfo.numchannels = waveFormat.nChannels; // Must specify for FMOD_OPENRAW

result = audioSystem->createSound(&audioBuffer.front(), FMOD_OPENRAW | FMOD_OPENMEMORY,
&exinfo, &audio);

// Get rid of excess memory
audioBuffer.swap(std::vector<char>());

if(FMOD_OK != result)
{
throw(std::runtime_error("Could not load sound"));
}

// success
hasAudio = true;
}

void Movie::process_video()
{
HRESULT error = AVIFileGetStream(aviFile, &videoStream, streamtypeVIDEO, 0);

if(error)
{
throw(std::runtime_error("Error getting video stream"));
}

// Get the stream info
error = AVIStreamInfo(videoStream, &videoStreamInfo, sizeof(videoStreamInfo));

if(error)
{
throw(std::runtime_error("Error getting video stream information"));
}

// Final frame
lastFrame = AVIStreamLength(videoStream);

// Time to display each frame
mpf = (double)AVIStreamSampleToTime(videoStream, lastFrame) / (double)lastFrame;

// Get decompressor
frameDecompressor = AVIStreamGetFrameOpen(videoStream, nullptr);

if(nullptr == frameDecompressor)
{
throw (std::runtime_error("Could not get decompressor"));
}
}

void Movie::init_opengl()
{
// Get video properties

LPBITMAPINFOHEADER lpbi = (LPBITMAPINFOHEADER)AVIStreamGetFrame(frameDecompressor, 0);

// width, height, bit count
width = lpbi->biWidth;
height = lpbi->biHeight;
bytesPerPixel = lpbi->biBitCount / 8;
dataSize = width * height * bytesPerPixel;

glGenBuffers(1, &pbo);
glBindBuffer(GL_PIXEL_UNPACK_BUFFER, pbo);
glBufferData(GL_PIXEL_UNPACK_BUFFER, dataSize, nullptr, GL_STREAM_DRAW);

glGenTextures(1, &texture);
glBindTexture(GL_TEXTURE_2D, texture);
glTexParameteri(GL_TEXTURE_2D, GL_TEXTURE_WRAP_S, GL_CLAMP_TO_EDGE);
glTexParameteri(GL_TEXTURE_2D, GL_TEXTURE_WRAP_T, GL_CLAMP_TO_EDGE);
glTexParameteri(GL_TEXTURE_2D, GL_TEXTURE_MIN_FILTER, GL_LINEAR);
glTexParameteri(GL_TEXTURE_2D, GL_TEXTURE_MAG_FILTER, GL_LINEAR);

GLint format = bytesPerPixel == 3 ? GL_RGB : GL_RGBA;
glTexImage2D(GL_TEXTURE_2D, 0, format, width, height, 0, GL_BGR, GL_UNSIGNED_BYTE, nullptr);

// unbind
glBindBuffer(GL_PIXEL_UNPACK_BUFFER, 0);
hasVideo = true;
}

void Movie::grab_frame()
{
static DWORD previousFrame = 0;

if((previousFrame != currentFrame) || (0 == currentFrame))
{
// Update the texture only if the previous frame does not equal the current frame or
// it's the first frame (frame #0)
LPBITMAPINFOHEADER lpbi = (LPBITMAPINFOHEADER)AVIStreamGetFrame(frameDecompressor, currentFrame);
// Get pointer to the data
char *data = (char*)lpbi + lpbi->biSize + (lpbi->biClrUsed * sizeof(RGBQUAD));

// Update the pbo and texture
glBindBuffer(GL_PIXEL_UNPACK_BUFFER, pbo);
glBufferSubData(GL_PIXEL_UNPACK_BUFFER, 0, dataSize, data);

previousFrame = currentFrame;
}
}

void Movie::play()
{
if(STOPPED == playState)
{
// Start audio first
audioSystem->playSound(FMOD_CHANNEL_FREE, audio, false, &channel);
timer.start();
playState = PLAYING;
}
}

void Movie::stop()
{
if(PLAYING == playState)
{
if(hasAudio)
channel->stop();

playState = STOPPED;

currentFrame = 0;
nextFrame = 0;
}
}

void Movie::bind_texture()
{
// TODO previousFrame
static DWORD previousFrame = 0;

if((previousFrame != currentFrame) || (0 == currentFrame))
{
glBindBuffer(GL_PIXEL_UNPACK_BUFFER, pbo);
glBindTexture(GL_TEXTURE_2D, texture);
GLint format = bytesPerPixel == 3 ? GL_RGB : GL_RGBA;
glTexImage2D(GL_TEXTURE_2D, 0, format, width, height, 0, GL_BGR, GL_UNSIGNED_BYTE, nullptr);
glBindBuffer(GL_PIXEL_UNPACK_BUFFER, 0);
previousFrame = currentFrame;
}
else
{
glBindTexture(GL_TEXTURE_2D, texture);
}
}

bool Movie::is_playing()const
{
return (PLAYING == playState);
}

void Movie::update()
{
if(hasAudio)
audioSystem->update();

if(hasVideo && (PLAYING == playState))
{
nextFrame += timer.milliseconds();
currentFrame = (DWORD)(nextFrame / mpf);

if(currentFrame >= lastFrame)
{
currentFrame = 0;
nextFrame = 0;
playState = STOPPED;
}

grab_frame();
}
}

void Movie::seek_forward()
{
if(PLAYING == playState)
{
long sample = AVIStreamTimeToSample(videoStream, (LONG)nextFrame + seekMilliseconds);

nextFrame = AVIStreamSampleToTime(videoStream, sample);


// reset
timer.milliseconds();

if(hasAudio)
channel->setPosition((unsigned int)nextFrame, FMOD_TIMEUNIT_MS);

currentFrame = DWORD(nextFrame / mpf);


if(currentFrame <= 0 || (currentFrame >= lastFrame))
{
channel->stop();
currentFrame = 0;
playState = STOPPED;
nextFrame = 0;
}
}
}

void Movie::seek_reverse()
{
if(PLAYING == playState)
{
long sample = AVIStreamTimeToSample(videoStream, (LONG)nextFrame - seekMilliseconds);

if(-1 == sample)
{
// probably seeked before initial position
nextFrame = 0;
if(hasAudio)
channel->setPosition(0, FMOD_TIMEUNIT_MS);
timer.milliseconds();
return;
}

nextFrame = AVIStreamSampleToTime(videoStream, sample);
if(hasAudio)
channel->setPosition((unsigned int)nextFrame, FMOD_TIMEUNIT_MS);
// reset
timer.milliseconds();

currentFrame = DWORD(nextFrame / mpf);
}
}

void Movie::seek_to_position(DWORD positionInMs)
{
if(PLAYING == playState)
{
long sample = AVIStreamTimeToSample(videoStream, positionInMs);

if(-1 == sample)
{
// Error, do nothing or throw something
return;
}

nextFrame = AVIStreamSampleToTime(videoStream, sample);

if(hasAudio)
channel->setPosition((unsigned int)nextFrame, FMOD_TIMEUNIT_MS);
//reset
timer.milliseconds();

currentFrame = DWORD(nextFrame / mpf);
}
}

void Movie::mute()
{
if(PLAYING == playState && hasAudio)
{
channel->setMute(true);
}
}

void Movie::unmute()
{
if(PLAYING == playState && hasAudio)
{
channel->setMute(false);
}
}





MyTimer.hpp

#ifndef MYTIMER_HPP
#define MYTIMER_HPP

#include <Windows.h>

namespace bj
{

class Timer
{
public:
Timer();


void start(); // start or reset timer
double seconds(); // returns seconds since last time seconds or milliseconds has be called
double milliseconds(); // returns seconds since last time seconds or milliseconds has be called
double delta_from_start()const; // Returns

enum MODE {STOPPED, RUNNING, PAUSED};

private:
void set_state(MODE m);
MODE get_state()const;
LARGE_INTEGER startTime;
LARGE_INTEGER currentTime;
LARGE_INTEGER frequency;
MODE mode;

};
}





Timer.cpp

#include "MyTimer.hpp"

using namespace bj;

Timer::Timer():
mode(STOPPED)
{
QueryPerformanceFrequency(&frequency);
}

void Timer::start()
{
QueryPerformanceCounter(&currentTime);
startTime = currentTime;
set_state(RUNNING);
}



double Timer::seconds()
{
LARGE_INTEGER newTime;
QueryPerformanceCounter(&newTime);

double seconds = ((double)(newTime.QuadPart - currentTime.QuadPart)) / frequency.QuadPart;
currentTime = newTime;
return (seconds);
}

double Timer::milliseconds()
{
LARGE_INTEGER newTime;
double milliseconds;

QueryPerformanceCounter(&newTime);
milliseconds = (((double)(newTime.QuadPart - currentTime.QuadPart) / frequency.QuadPart)) * 1000.0;
currentTime = newTime;
return (milliseconds);
}

double Timer::delta_from_start()const
{
LARGE_INTEGER newTime;
QueryPerformanceCounter(&newTime);

return (((double)(newTime.QuadPart - startTime.QuadPart)) / frequency.QuadPart);
}

void Timer::set_state(MODE m)
{
mode = m;
}

Timer::MODE Timer::get_state()const
{
return (mode);
}





I hope this serves you well.

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      I'm trying to learn OpenGL through a website and have proceeded until this page of it. The output is a simple triangle. The problem is the complexity.
      I have read that page several times and tried to analyse the code but I haven't understood the code properly and completely yet. This is the code:
       
      #include <glad/glad.h> #include <GLFW/glfw3.h> #include <C:\Users\Abbasi\Desktop\std_lib_facilities_4.h> using namespace std; //****************************************************************************** void framebuffer_size_callback(GLFWwindow* window, int width, int height); void processInput(GLFWwindow *window); // settings const unsigned int SCR_WIDTH = 800; const unsigned int SCR_HEIGHT = 600; const char *vertexShaderSource = "#version 330 core\n" "layout (location = 0) in vec3 aPos;\n" "void main()\n" "{\n" " gl_Position = vec4(aPos.x, aPos.y, aPos.z, 1.0);\n" "}\0"; const char *fragmentShaderSource = "#version 330 core\n" "out vec4 FragColor;\n" "void main()\n" "{\n" " FragColor = vec4(1.0f, 0.5f, 0.2f, 1.0f);\n" "}\n\0"; //******************************* int main() { // glfw: initialize and configure // ------------------------------ glfwInit(); glfwWindowHint(GLFW_CONTEXT_VERSION_MAJOR, 3); glfwWindowHint(GLFW_CONTEXT_VERSION_MINOR, 3); glfwWindowHint(GLFW_OPENGL_PROFILE, GLFW_OPENGL_CORE_PROFILE); // glfw window creation GLFWwindow* window = glfwCreateWindow(SCR_WIDTH, SCR_HEIGHT, "My First Triangle", nullptr, nullptr); if (window == nullptr) { cout << "Failed to create GLFW window" << endl; glfwTerminate(); return -1; } glfwMakeContextCurrent(window); glfwSetFramebufferSizeCallback(window, framebuffer_size_callback); // glad: load all OpenGL function pointers if (!gladLoadGLLoader((GLADloadproc)glfwGetProcAddress)) { cout << "Failed to initialize GLAD" << endl; return -1; } // build and compile our shader program // vertex shader int vertexShader = glCreateShader(GL_VERTEX_SHADER); glShaderSource(vertexShader, 1, &vertexShaderSource, nullptr); glCompileShader(vertexShader); // check for shader compile errors int success; char infoLog[512]; glGetShaderiv(vertexShader, GL_COMPILE_STATUS, &success); if (!success) { glGetShaderInfoLog(vertexShader, 512, nullptr, infoLog); cout << "ERROR::SHADER::VERTEX::COMPILATION_FAILED\n" << infoLog << endl; } // fragment shader int fragmentShader = glCreateShader(GL_FRAGMENT_SHADER); glShaderSource(fragmentShader, 1, &fragmentShaderSource, nullptr); glCompileShader(fragmentShader); // check for shader compile errors glGetShaderiv(fragmentShader, GL_COMPILE_STATUS, &success); if (!success) { glGetShaderInfoLog(fragmentShader, 512, nullptr, infoLog); cout << "ERROR::SHADER::FRAGMENT::COMPILATION_FAILED\n" << infoLog << endl; } // link shaders int shaderProgram = glCreateProgram(); glAttachShader(shaderProgram, vertexShader); glAttachShader(shaderProgram, fragmentShader); glLinkProgram(shaderProgram); // check for linking errors glGetProgramiv(shaderProgram, GL_LINK_STATUS, &success); if (!success) { glGetProgramInfoLog(shaderProgram, 512, nullptr, infoLog); cout << "ERROR::SHADER::PROGRAM::LINKING_FAILED\n" << infoLog << endl; } glDeleteShader(vertexShader); glDeleteShader(fragmentShader); // set up vertex data (and buffer(s)) and configure vertex attributes float vertices[] = { -0.5f, -0.5f, 0.0f, // left 0.5f, -0.5f, 0.0f, // right 0.0f, 0.5f, 0.0f // top }; unsigned int VBO, VAO; glGenVertexArrays(1, &VAO); glGenBuffers(1, &VBO); // bind the Vertex Array Object first, then bind and set vertex buffer(s), //and then configure vertex attributes(s). glBindVertexArray(VAO); glBindBuffer(GL_ARRAY_BUFFER, VBO); glBufferData(GL_ARRAY_BUFFER, sizeof(vertices), vertices, GL_STATIC_DRAW); glVertexAttribPointer(0, 3, GL_FLOAT, GL_FALSE, 3 * sizeof(float), (void*)0); glEnableVertexAttribArray(0); // note that this is allowed, the call to glVertexAttribPointer registered VBO // as the vertex attribute's bound vertex buffer object so afterwards we can safely unbind glBindBuffer(GL_ARRAY_BUFFER, 0); // You can unbind the VAO afterwards so other VAO calls won't accidentally // modify this VAO, but this rarely happens. Modifying other // VAOs requires a call to glBindVertexArray anyways so we generally don't unbind // VAOs (nor VBOs) when it's not directly necessary. glBindVertexArray(0); // uncomment this call to draw in wireframe polygons. //glPolygonMode(GL_FRONT_AND_BACK, GL_LINE); // render loop while (!glfwWindowShouldClose(window)) { // input // ----- processInput(window); // render // ------ glClearColor(0.2f, 0.3f, 0.3f, 1.0f); glClear(GL_COLOR_BUFFER_BIT); // draw our first triangle glUseProgram(shaderProgram); glBindVertexArray(VAO); // seeing as we only have a single VAO there's no need to // bind it every time, but we'll do so to keep things a bit more organized glDrawArrays(GL_TRIANGLES, 0, 3); // glBindVertexArray(0); // no need to unbind it every time // glfw: swap buffers and poll IO events (keys pressed/released, mouse moved etc.) glfwSwapBuffers(window); glfwPollEvents(); } // optional: de-allocate all resources once they've outlived their purpose: glDeleteVertexArrays(1, &VAO); glDeleteBuffers(1, &VBO); // glfw: terminate, clearing all previously allocated GLFW resources. glfwTerminate(); return 0; } //************************************************** // process all input: query GLFW whether relevant keys are pressed/released // this frame and react accordingly void processInput(GLFWwindow *window) { if (glfwGetKey(window, GLFW_KEY_ESCAPE) == GLFW_PRESS) glfwSetWindowShouldClose(window, true); } //******************************************************************** // glfw: whenever the window size changed (by OS or user resize) this callback function executes void framebuffer_size_callback(GLFWwindow* window, int width, int height) { // make sure the viewport matches the new window dimensions; note that width and // height will be significantly larger than specified on retina displays. glViewport(0, 0, width, height); } As you see, about 200 lines of complicated code only for a simple triangle. 
      I don't know what parts are necessary for that output. And also, what the correct order of instructions for such an output or programs is, generally. That start point is too complex for a beginner of OpenGL like me and I don't know how to make the issue solved. What are your ideas please? What is the way to figure both the code and the whole program out correctly please?
      I wish I'd read a reference that would teach me OpenGL through a step-by-step method. 
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