triangle dont appear in opengl? [closed] - c++

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I can get Opengl triangle to appear.
#include <GL/glew.h>
#include <GLFW/glfw3.h>
#include <iostream>
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";
void framebuffer_size_callback(GLFWwindow* window, int width, int height)
{
glViewport(0, 0, width, height);
}
void processInput(GLFWwindow *window) {
if (glfwGetKey(window, GLFW_KEY_ESCAPE) == GLFW_PRESS) { glfwSetWindowShouldClose(window, true); }
}
int main()
{
glewExperimental = GL_TRUE;
glfwInit();
glfwWindowHint(GLFW_CONTEXT_VERSION_MAJOR,3);
glfwWindowHint(GLFW_CONTEXT_VERSION_MINOR,3);
glfwWindowHint(GLFW_OPENGL_PROFILE, GLFW_OPENGL_CORE_PROFILE);
GLFWwindow* window{ glfwCreateWindow(800,600,"Opengl",NULL,NULL) };
glfwSetFramebufferSizeCallback(window, framebuffer_size_callback);
glfwMakeContextCurrent(window);
GLenum err = glewInit();
if (glewInit() != GLEW_OK) { std::cout << glewGetErrorString(err); return -1; }
int vertexShader;
vertexShader = glCreateShader(GL_VERTEX_SHADER);
glShaderSource(vertexShader, 1, &vertexShaderSource, NULL);
glCompileShader(vertexShader);
int fragmentShader;
fragmentShader = glCreateShader(GL_FRAGMENT_SHADER);
glShaderSource(fragmentShader,1,&fragmentShaderSource,NULL);
glCompileShader(fragmentShader);
int shaderProgram = glCreateProgram();
glAttachShader(shaderProgram,vertexShader);
glAttachShader(shaderProgram,fragmentShader);
glLinkProgram(shaderProgram);
glDeleteShader(vertexShader);
glDeleteShader(fragmentShader);
float triangle[]{ -0.5f,-0.5f,0.0f,
0.5f,-0.5f,0.0,
0.0f,-0.5f,0.0f };
unsigned int VAO,buffer;
glGenVertexArrays(1, &VAO);
glBindVertexArray(VAO);
glGenBuffers(1, &buffer);
glBindBuffer(GL_ARRAY_BUFFER, buffer);
glBufferData(GL_ARRAY_BUFFER, sizeof(triangle), triangle, GL_STATIC_DRAW);
glVertexAttribPointer(0, 3, GL_FLOAT, GL_FALSE, 3*sizeof(float), (void*)0);
glEnableVertexAttribArray(0);
glBindBuffer(GL_ARRAY_BUFFER,0);
glBindVertexArray(0);
if (window == NULL) {
std::cout << "Window is null";
glfwTerminate();
return -1;
}
while (!glfwWindowShouldClose(window))
{
processInput(window);
glClearColor(0.2f, 0.2f, 0.2f, 1.0f);
glClear(GL_COLOR_BUFFER_BIT);
glUseProgram(shaderProgram);
glBindVertexArray(VAO);
glDrawArrays(GL_TRIANGLES,0,3);
glfwSwapBuffers(window);
glfwPollEvents();
}
glfwTerminate();
return 0;
}

Answer 1

All your triangle vertices are colinear, resulting in a degenerate triangle
Bumping the y-coordinate of the 3rd point up to 0.5 works for me:
float triangle[]
{
-0.5f, -0.5f, 0.0f,
0.5f, -0.5f, 0.0f,
0.0f, 0.5f, 0.0f,
};
All together:
#include <GL/glew.h>
#include <GLFW/glfw3.h>
#include <iostream>
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";
void framebuffer_size_callback( GLFWwindow* window, int width, int height )
{
glViewport( 0, 0, width, height );
}
void processInput( GLFWwindow* window )
{
if( glfwGetKey( window, GLFW_KEY_ESCAPE ) == GLFW_PRESS )
{
glfwSetWindowShouldClose( window, true );
}
}
int main()
{
glewExperimental = GL_TRUE;
glfwInit();
glfwWindowHint( GLFW_CONTEXT_VERSION_MAJOR, 3 );
glfwWindowHint( GLFW_CONTEXT_VERSION_MINOR, 3 );
glfwWindowHint( GLFW_OPENGL_PROFILE, GLFW_OPENGL_CORE_PROFILE );
GLFWwindow* window{ glfwCreateWindow( 800, 600, "Opengl", NULL, NULL ) };
glfwSetFramebufferSizeCallback( window, framebuffer_size_callback );
glfwMakeContextCurrent( window );
GLenum err = glewInit();
if( glewInit() != GLEW_OK )
{
std::cout << glewGetErrorString( err );
return -1;
}
int vertexShader;
vertexShader = glCreateShader( GL_VERTEX_SHADER );
glShaderSource( vertexShader, 1, &vertexShaderSource, NULL );
glCompileShader( vertexShader );
int fragmentShader;
fragmentShader = glCreateShader( GL_FRAGMENT_SHADER );
glShaderSource( fragmentShader, 1, &fragmentShaderSource, NULL );
glCompileShader( fragmentShader );
int shaderProgram = glCreateProgram();
glAttachShader( shaderProgram, vertexShader );
glAttachShader( shaderProgram, fragmentShader );
glLinkProgram( shaderProgram );
glDeleteShader( vertexShader );
glDeleteShader( fragmentShader );
float triangle[]{
-0.5f, -0.5f, 0.0f, 0.5f, -0.5f, 0.0f, 0.0f, 0.5f, 0.0f,
};
unsigned int VAO, buffer;
glGenVertexArrays( 1, &VAO );
glBindVertexArray( VAO );
glGenBuffers( 1, &buffer );
glBindBuffer( GL_ARRAY_BUFFER, buffer );
glBufferData(
GL_ARRAY_BUFFER, sizeof( triangle ), triangle, GL_STATIC_DRAW );
glVertexAttribPointer(
0, 3, GL_FLOAT, GL_FALSE, 3 * sizeof( float ), (void*)0 );
glEnableVertexAttribArray( 0 );
glBindBuffer( GL_ARRAY_BUFFER, 0 );
glBindVertexArray( 0 );
if( window == NULL )
{
std::cout << "Window is null";
glfwTerminate();
return -1;
}
while( !glfwWindowShouldClose( window ) )
{
processInput( window );
glClearColor( 0.2f, 0.2f, 0.2f, 1.0f );
glClear( GL_COLOR_BUFFER_BIT );
glUseProgram( shaderProgram );
glBindVertexArray( VAO );
glDrawArrays( GL_TRIANGLES, 0, 3 );
glfwSwapBuffers( window );
glfwPollEvents();
}
glfwTerminate();
return 0;
}