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OpenGL Why triangle is not drawing?

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Hi everybody! Today i've started to learn OpenGL and have some problems with it.

I tried to draw a triangle but i failed? Can't understand the problem, please help newbie)

 

CPP CODE

 

#include <glew.h>
#include <freeglut.h>
#include <iostream>
#include <fstream>
#include <string>


using namespace std;


GLuint vbo, shader, vs, ps;


GLfloat verts[] =
{
    0.75f, 0.75f, 0.0f, 1.0f,
    0.75f, -0.75f, 0.0f, 1.0f,
    -0.75f, -0.75f, 0.0f, 1.0f,
};


GLuint CreateShader(GLenum type, const char* src);
GLuint CreateProgram(GLuint vs, GLuint ps);


void init()
{
glGenBuffers(1, &vbo);
glBindBuffer(GL_ARRAY_BUFFER, vbo);
glBufferData(GL_ARRAY_BUFFER, 12 * sizeof(GLfloat), verts, GL_STATIC_DRAW);
glVertexAttribPointer(0, 4, GL_FLOAT, GL_FALSE, 0, 0);
glEnableVertexAttribArray(0);


ifstream f1, f2;
string   v,  p, tmp;


f1.open("v.vert");
f2.open("f.frag");


if(!f1.is_open() || !f2.is_open())
{
glDeleteBuffers(1, &vbo);
exit(1);
}


while(!f1.eof())
{
std::getline(f1, tmp);


v += tmp + "\n";


tmp.clear();
}


while(!f2.eof())
{
std::getline(f2, tmp);


p += tmp + "\n";


tmp.clear();
}


vs     = CreateShader(GL_VERTEX_SHADER, v.c_str());
ps     = CreateShader(GL_FRAGMENT_SHADER, p.c_str());
shader = CreateProgram(vs, ps);


if(shader == -1) 
{
glDeleteBuffers(1, &vbo);
glDeleteShader(vs);
glDeleteShader(ps);


exit(1);
}


glUseProgram(shader);
glDeleteShader(vs);
glDeleteShader(ps);


f1.close();
f2.close();
}




void display()
{
glClearColor(1.0f, 1.0f, 0.0f, 1.0f);
glClear(GL_COLOR_BUFFER_BIT);
glDrawArrays(GL_TRIANGLES, 0, 3);
glFlush();
glutSwapBuffers();
}


int main(int argc, char **argv)
{
glutInit(&argc, argv);
glutInitDisplayMode(GLUT_RGBA);
glutInitWindowSize(512, 512);
glutInitContextVersion(4, 3);
glutInitContextProfile(GLUT_CORE_PROFILE);
glutCreateWindow(argv[0]); 


if(glewInit())
{
return 0;
}


init();


glutDisplayFunc(display);
glutMainLoop();


return 0;
}


GLuint CreateShader(GLenum type, const GLchar* src)
{
GLuint res = glCreateShader(type);
GLint compileStatus;


glShaderSource(res, 1, &src, nullptr);
glCompileShader(res);
glGetShaderiv(res, GL_COMPILE_STATUS, &compileStatus);


if(compileStatus == GL_FALSE)
{
GLint   infoLength;
GLchar *infoLog = nullptr;


glGetShaderiv(res, GL_INFO_LOG_LENGTH, &infoLength);


infoLog = new GLchar[infoLength + 1];


glGetShaderInfoLog(res, infoLength, nullptr, infoLog);


cout << infoLog << endl;


delete []infoLog;
}


return res;
}


GLuint CreateProgram(GLuint vs, GLuint fs)
{
GLuint prog = glCreateProgram();
GLint status;


glAttachShader(prog, vs);
glAttachShader(prog, ps);
glLinkProgram(prog);
glGetProgramiv(prog, GL_LINK_STATUS, &status);
glDetachShader(prog, vs);
glDetachShader(prog, fs);


if(status == GL_FALSE) 
{
return -1;
}


return prog;
}
 
Vertex shader
 
#version 430 core


layout(location = 0) in vec4 position;


void main()
{
gl_Position = position;
}
 
Fragment Shader
 
#version 430 core


out vec4 outColor;


void main()
{
outColor = vec4(1.0f, 1.0f, 1.0f, 1.0f);
}

 

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Renew my shader create function.

GLuint CreateProgram(GLuint vs, GLuint fs)
{
GLuint prog = glCreateProgram();
GLint status;


glAttachShader(prog, vs);
glAttachShader(prog, fs);
glLinkProgram(prog);
glGetProgramiv(prog, GL_LINK_STATUS, &status);
glDetachShader(prog, vs);
glDetachShader(prog, fs);


if(status == GL_FALSE) 
{
return -1;
}


return prog;
}

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Did you setup a projection matrix? ModelViewmatrix?

 

0.75f, 0.75f, 0.0f, 1.0f,

 

Change all the 0.0f's  to -10.0. If that doesnt work you need to setup a proper view and projection matrix.

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Rewrote programm and it works. Why? Please help.

 

#include <iostream>
#include <glew.h>
#include <glfw3.h>


GLfloat clearColor[] = { 1.0f, 1.0f, 1.0f, 1.0f };
GLuint vertexShader, fragmentShader, shaderProgram, vbo;


GLfloat vertices[] = { 0.0f, 0.5f, 
  0.5f, 0.0f, 
 -0.5f, 0.0f };


GLuint CreateShader(GLenum type, const GLchar* src);
GLuint CreateProgram(GLuint vShader, GLuint fShader);


void InitScene()
{
glGenBuffers(1, &vbo);
glBindBuffer(GL_ARRAY_BUFFER, vbo);
glBufferData(GL_ARRAY_BUFFER, sizeof(vertices), vertices, GL_STATIC_DRAW);
glBindBuffer(GL_ARRAY_BUFFER, 0);


GLchar vsrc[] = { "#version 430 core   \n"
 "layout(location = 0) in vec4 position; \n"
 "void main() {                          \n"
 "gl_Position = position;                \n"
 "}                                      \n" };


GLchar fsrc[] = { "#version 430 core    \n"
 "out vec4 resColor;    \n"
 "void main() {    \n"
 "resColor = vec4(1.0f, 0.0f, 0.0f, 1.0f);\n"
 "}    \n" };


vertexShader   = CreateShader(GL_VERTEX_SHADER, vsrc);
fragmentShader = CreateShader(GL_FRAGMENT_SHADER, fsrc);
shaderProgram  = CreateProgram(vertexShader, fragmentShader);


if(shaderProgram == -1) 
{
std::getchar();
exit(1);
}


glDeleteShader(vertexShader);
glDeleteShader(fragmentShader);
}


void ResizeCallback(GLFWwindow* wnd, int width, int height)
{
glViewport(0, 0, width, height);
}


void Draw()
{
glBindBuffer(GL_ARRAY_BUFFER, vbo);
glVertexAttribPointer(0, 2, GL_FLOAT, GL_FALSE, 0, 0);
glEnableVertexAttribArray(0);
glUseProgram(shaderProgram);


glClearBufferfv(GL_COLOR, 0, clearColor);
glDrawArrays(GL_TRIANGLES, 0, 3);
glFlush();


glBindBuffer(GL_ARRAY_BUFFER, 0);
glUseProgram(0);
}


void Terminate()
{
glDeleteBuffers(1, &vbo);
glDeleteProgram(shaderProgram);
}


int main(int argc, char** argv)
{
if(!glfwInit()) return 0;


GLFWwindow* wnd = glfwCreateWindow(640, 480, "Hello triangle", nullptr, nullptr);


if(!wnd) 
{
glfwTerminate();
return 0;
}


glfwMakeContextCurrent(wnd);
glewExperimental = true;


if(glewInit() != GLEW_OK)
{
glfwTerminate();
return 0;
}


glfwSetWindowSizeCallback(wnd, ResizeCallback);


InitScene();


while(!glfwWindowShouldClose(wnd))
{
Draw();
glfwSwapBuffers(wnd);
glfwPollEvents();
}


Terminate();


glfwDestroyWindow(wnd);
glfwTerminate();


return 0;
}


GLuint CreateProgram(GLuint vShader, GLuint fShader)
{
GLuint p = glCreateProgram();


glAttachShader(p, vShader);
glAttachShader(p, fShader);
glLinkProgram(p);


GLint status;


glGetProgramiv(p, GL_LINK_STATUS, &status);


if(status == GL_FALSE)
{
glGetProgramiv(p, GL_INFO_LOG_LENGTH, &status);


GLchar* infoLog = new GLchar[status + 1];


glGetProgramInfoLog(p, status, nullptr, infoLog);


std::cout << "Program error: \n" << infoLog << "\n";


return -1;
}


return p;
}


GLuint CreateShader(GLenum type, const GLchar* src)
{
GLuint s      = glCreateShader(type);
GLint  status = 0;


glShaderSource(s, 1, &src, nullptr);
glCompileShader(s);
glGetShaderiv(s, GL_COMPILE_STATUS, &status);


if(status == GL_FALSE)
{
glGetShaderiv(s, GL_INFO_LOG_LENGTH, &status);


GLchar* infoLog = new GLchar[status + 1];


glGetShaderInfoLog(s, status, nullptr, infoLog);


switch(type)
{
case GL_VERTEX_SHADER:   std::cout << "Vertex shader error: \n";   break;
case GL_FRAGMENT_SHADER: std::cout << "Fragment shader error: \n"; break;
}


std::cout << infoLog << "\n";


delete []infoLog;


return -1;
}


return s;
}

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Maybe your triangle is getting culled, because the vertices are counter-clockwise.

If you swap the last two vertices, thew will be clockwise, and the triangle should show (unless there's another problem):

GLfloat verts[] =
{
    0.75f, 0.75f, 0.0f, 1.0f,
    -0.75f, -0.75f, 0.0f, 1.0f,

    0.75f, -0.75f, 0.0f, 1.0f
};

Or was it counter-clockwise=front by default for OpenGL? In that case, nevermind... (or check that you're not doing glFrontFace(GL_CW) anywhere).

 

Never mind that... smile.png

 

I think the problem is with your glEnableVertexAttribArray call... In the first example, you had it set the format of the VBO to 4-float component values per vertex, which I assume you wanted to be two position components for the clip-space position and two texture coordinates? But in your vertex shader, you are treating all 4 components as the position: vec4 position (no texture coords). And those "texture coordinates" do not work well as "vertex.z" and "vertex.w" components - the vertex.w component should always be greater than 0.0 - and this is ok in your first example, so maybe the vertex.z component is not ok? In OpenGL, vertices at the z=0 clip position should be at the center of the clip space, but maybe you want them at the front/near plane of the frustum?

 

The second example works because you reduced the VBO format to two-float components per vertex, without z and w values, which are probably filled to correct values by the GLSL compiler?

Edited by tonemgub

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tonemgub

Thank you for your ansver!

But my program wasn't supposed to have texCoord. 

I put values from the first programm to the second with 4 floatin point values per vertex and it work!.

(My english is not so good, i'm from Ukraine).

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I put values from the first programm to the second with 4 floatin point values per vertex and it work!.

Yes, I realize now those are valid z and w components... I don't know much about OpenGL - I always have to compare it to Direct3D, so those were just silly assumptions. Sorry.

 

This struck me a bit now:

 

 


For what projection matrix? Points already in clip space.

I think you do need a projection matrix, because it is used to convert your clip space coordinates to the final screen coordinates... or not? smile.png

Here's an article that explains all of the operations OpenGL performs on your vertices behind the scene: http://trac.bookofhook.com/bookofhook/trac.cgi/wiki/MousePicking

 

Otherwise, the only possibility left is that your original z and w values of 0.0 and 1.0 are getting clipped, although I can't tell you for sure if that is the case. You should try changing the values to see what difference it makes.

 

Wait... did your original example also have a glViewport call? I don't see it anywhere. I think this explains your problem: https://www.opengl.org/discussion_boards/showthread.php/130557-GLUT-glViewPort-problem?s=368fb74d33486873671310aae312cda4&p=975333&viewfull=1#post975333

I think you can fix the first example by adding a call to glutShowWindow right after glutCreateWindow - this will cause your window to be resized to the coordinates you passed in glutInitWindowSize. But the proper way is to use a resize callback like that post suggest.

Edited by tonemgub

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      Brain Class
      #include "Brain.h" #include "Sprite.h" #include "Window.h" struct Brain::Implementation { //Just A Flag. bool started; //Window Pointer. Window *window; //Sprite Pointer. Sprite *sprite; }; Brain::Brain(Window *window, Sprite *sprite) { //Create Pointer To Implementation. m_Impl = new Implementation(); //Initialize Implementation. m_Impl->started = true; m_Impl->window = window; m_Impl->sprite = sprite; } Brain::~Brain() { //Delete Pointer To Implementation. delete m_Impl; } void Brain::Start() { } void Brain::Update() { } Window * Brain::GetWindow() { return m_Impl->window; } Sprite * Brain::GetSprite() { return m_Impl->sprite; } bool Brain::GetStart() { return m_Impl->started; } void Brain::SetStart(bool value) { m_Impl->started = value; } Script Class (Its a Brain Subclass!!!)
      #include "Script.h" Script::Script(Window *window, Sprite *sprite) : Brain(window, sprite) { } Script::~Script() { } void Script::Start() { std::cout << "Game Started!" << std::endl; } void Script::Update() { Input *input = this->GetWindow()->GetInput(); Sprite *sp = this->GetSprite(); //Move this sprite. this->GetSprite()->Move(200 * this->GetWindow()->GetDeltaTime(), input->GetKeyDown("left"), input->GetKeyDown("right"), input->GetKeyDown("up"), input->GetKeyDown("down")); std::cout << sp->GetTag().c_str() << ".x = " << sp->GetPos()->x << ", " << sp->GetTag().c_str() << ".y = " << sp->GetPos()->y << std::endl; }  
      Main:
      #include "SpaceShooterEngine.h" #include "Script.h" int main() { Window w("title", 600,600); Scene *scene = new Scene(); Sprite *player = new Sprite("Resources/Images/player.png", "Player", 100,100); Sprite *other = new Sprite("Resources/Images/cherno.png", "Other", 400, 100); Sprite *other2 = new Sprite("Resources/Images/cherno.png", "Other", 300, 400); Brain *brain = new Script(&w, player); player->AddBrain(brain); scene->AddSprite(player); scene->AddSprite(other); scene->AddSprite(other2); w.LoadScene(scene); w.MainLoop(); return 0; }  
       
      I literally can't find what is wrong. If you need more code, ask me to post it. I will also attach all the source files.
      Brain.cpp
      Error.cpp
      IndexBuffer.cpp
      Input.cpp
      Renderer.cpp
      Scene.cpp
      Shader.cpp
      Sprite.cpp
      Texture.cpp
      VertexArray.cpp
      VertexBuffer.cpp
      VertexBufferLayout.cpp
      Window.cpp
      Brain.h
      Error.h
      IndexBuffer.h
      Input.h
      Renderer.h
      Scene.h
      Shader.h
      SpaceShooterEngine.h
      Sprite.h
      Texture.h
      VertexArray.h
      VertexBuffer.h
      VertexBufferLayout.h
      Window.h
    • By Cristian Decu
      Hello fellow programmers,
      For a couple of days now i've decided to build my own planet renderer just to see how floating point precision issues
      can be tackled. As you probably imagine, i've quickly faced FPP issues when trying to render absurdly large planets.
       
      I have used the classical quadtree LOD approach;
      I've generated my grids with 33 vertices, (x: -1 to 1, y: -1 to 1, z = 0).
      Each grid is managed by a TerrainNode class that, depending on the side it represents (top, bottom, left right, front, back),
      creates a special rotation-translation matrix that moves and rotates the grid away from the origin so that when i finally
      normalize all the vertices on my vertex shader i can get a perfect sphere.
      T = glm::translate(glm::dmat4(1.0), glm::dvec3(0.0, 0.0, 1.0)); R = glm::rotate(glm::dmat4(1.0), glm::radians(180.0), glm::dvec3(1.0, 0.0, 0.0)); sides[0] = new TerrainNode(1.0, radius, T * R, glm::dvec2(0.0, 0.0), new TerrainTile(1.0, SIDE_FRONT)); T = glm::translate(glm::dmat4(1.0), glm::dvec3(0.0, 0.0, -1.0)); R = glm::rotate(glm::dmat4(1.0), glm::radians(0.0), glm::dvec3(1.0, 0.0, 0.0)); sides[1] = new TerrainNode(1.0, radius, R * T, glm::dvec2(0.0, 0.0), new TerrainTile(1.0, SIDE_BACK)); // So on and so forth for the rest of the sides As you can see, for the front side grid, i rotate it 180 degrees to make it face the camera and push it towards the eye;
      the back side is handled almost the same way only that i don't need to rotate it but simply push it away from the eye.
      The same technique is applied for the rest of the faces (obviously, with the proper rotations / translations).
      The matrix that result from the multiplication of R and T (in that particular order) is send to my vertex shader as `r_Grid'.
      // spherify vec3 V = normalize((r_Grid * vec4(r_Vertex, 1.0)).xyz); gl_Position = r_ModelViewProjection * vec4(V, 1.0); The `r_ModelViewProjection' matrix is generated on the CPU in this manner.
      // No the most efficient way, but it works. glm::dmat4 Camera::getMatrix() { // Create the view matrix // Roll, Yaw and Pitch are all quaternions. glm::dmat4 View = glm::toMat4(Roll) * glm::toMat4(Pitch) * glm::toMat4(Yaw); // The model matrix is generated by translating in the oposite direction of the camera. glm::dmat4 Model = glm::translate(glm::dmat4(1.0), -Position); // Projection = glm::perspective(fovY, aspect, zNear, zFar); // zNear = 0.1, zFar = 1.0995116e12 return Projection * View * Model; } I managed to get rid of z-fighting by using a technique called Logarithmic Depth Buffer described in this article; it works amazingly well, no z-fighting at all, at least not visible.
      Each frame i'm rendering each node by sending the generated matrices this way.
      // set the r_ModelViewProjection uniform // Sneak in the mRadiusMatrix which is a matrix that contains the radius of my planet. Shader::setUniform(0, Camera::getInstance()->getMatrix() * mRadiusMatrix); // set the r_Grid matrix uniform i created earlier. Shader::setUniform(1, r_Grid); grid->render(); My planet's radius is around 6400000.0 units, absurdly large, but that's what i really want to achieve;
      Everything works well, the node's split and merge as you'd expect, however whenever i get close to the surface
      of the planet the rounding errors start to kick in giving me that lovely stairs effect.
      I've read that if i could render each grid relative to the camera i could get better precision on the surface, effectively
      getting rid of those rounding errors.
       
      My question is how can i achieve this relative to camera rendering in my scenario here?
      I know that i have to do most of the work on the CPU with double, and that's exactly what i'm doing.
      I only use double on the CPU side where i also do most of the matrix multiplications.
      As you can see from my vertex shader i only do the usual r_ModelViewProjection * (some vertex coords).
       
      Thank you for your suggestions!
       
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