Skip to content

@dlivingstone /Triangle_opengl_3_1.cpp
Created

Embed URL

HTTPS clone URL

Subversion checkout URL

You can clone with
or
.
Download ZIP
OpenGL 3.0+ Rendering Example - A complete and fairly minimal example of rendering with shaders
// Fragment Shader – file "minimal.frag"
#version 130
precision highp float; // needed only for version 1.30
in vec3 ex_Color;
out vec4 out_Color;
void main(void)
{
out_Color = vec4(ex_Color,1.0);
// Try replacing the above with the following:
//vec3 tmp_Color;
//tmp_Color = ex_Color.rrr;
//out_Color = vec4(tmp_Color,1.0);
}
// Vertex Shader – file "minimal.vert"
#version 130
in vec3 in_Position;
in vec3 in_Color;
out vec3 ex_Color;
void main(void)
{
ex_Color = in_Color;
gl_Position = vec4(in_Position, 1.0);
}
// Triangle_opengl_3_1
// A cross platform version of
// http://www.opengl.org/wiki/Tutorial:_OpenGL_3.1_The_First_Triangle_%28C%2B%2B/Win%29
// with some code from http://www.lighthouse3d.com/opengl/glsl/index.php?oglexample1
// and from the book OpenGL Shading Language 3rd Edition, p215-216
// Daniel Livingstone, October 2010
#include <GL/glew.h>
#define FREEGLUT_STATIC
#include <GL/freeglut.h>
#include <iostream>
#include <fstream>
#include <string>
using namespace std;
// Globals
// Real programs don't use globals :-D
// Data would normally be read from files
GLfloat vertices[] = { -1.0f,0.0f,0.0f,
0.0f,1.0f,0.0f,
0.0f,0.0f,0.0f };
GLfloat colours[] = { 1.0f, 0.0f, 0.0f,
0.0f, 1.0f, 0.0f,
0.0f, 0.0f, 1.0f };
GLfloat vertices2[] = { 0.0f,0.0f,0.0f,
0.0f,-1.0f,0.0f,
1.0f,0.0f,0.0f };
// two vertex array objects, one for each object drawn
unsigned int vertexArrayObjID[2];
// three vertex buffer objects in this example
unsigned int vertexBufferObjID[3];
// loadFile - loads text file into char* fname
// allocates memory - so need to delete after use
// size of file returned in fSize
char* loadFile(char *fname, GLint &fSize)
{
ifstream::pos_type size;
char * memblock;
string text;
// file read based on example in cplusplus.com tutorial
ifstream file (fname, ios::in|ios::binary|ios::ate);
if (file.is_open())
{
size = file.tellg();
fSize = (GLuint) size;
memblock = new char [size];
file.seekg (0, ios::beg);
file.read (memblock, size);
file.close();
cout << "file " << fname << " loaded" << endl;
text.assign(memblock);
}
else
{
cout << "Unable to open file " << fname << endl;
exit(1);
}
return memblock;
}
// printShaderInfoLog
// From OpenGL Shading Language 3rd Edition, p215-216
// Display (hopefully) useful error messages if shader fails to compile
void printShaderInfoLog(GLint shader)
{
int infoLogLen = 0;
int charsWritten = 0;
GLchar *infoLog;
glGetShaderiv(shader, GL_INFO_LOG_LENGTH, &infoLogLen);
// should additionally check for OpenGL errors here
if (infoLogLen > 0)
{
infoLog = new GLchar[infoLogLen];
// error check for fail to allocate memory omitted
glGetShaderInfoLog(shader,infoLogLen, &charsWritten, infoLog);
cout << "InfoLog:" << endl << infoLog << endl;
delete [] infoLog;
}
// should additionally check for OpenGL errors here
}
void init(void)
{
// Would load objects from file here - but using globals in this example
// Allocate Vertex Array Objects
glGenVertexArrays(2, &vertexArrayObjID[0]);
// Setup first Vertex Array Object
glBindVertexArray(vertexArrayObjID[0]);
glGenBuffers(2, vertexBufferObjID);
// VBO for vertex data
glBindBuffer(GL_ARRAY_BUFFER, vertexBufferObjID[0]);
glBufferData(GL_ARRAY_BUFFER, 9*sizeof(GLfloat), vertices, GL_STATIC_DRAW);
glVertexAttribPointer((GLuint)0, 3, GL_FLOAT, GL_FALSE, 0, 0);
glEnableVertexAttribArray(0);
// VBO for colour data
glBindBuffer(GL_ARRAY_BUFFER, vertexBufferObjID[1]);
glBufferData(GL_ARRAY_BUFFER, 9*sizeof(GLfloat), colours, GL_STATIC_DRAW);
glVertexAttribPointer((GLuint)1, 3, GL_FLOAT, GL_FALSE, 0, 0);
glEnableVertexAttribArray(1);
// Setup second Vertex Array Object
glBindVertexArray(vertexArrayObjID[1]);
glGenBuffers(1, &vertexBufferObjID[2]);
// VBO for vertex data
glBindBuffer(GL_ARRAY_BUFFER, vertexBufferObjID[2]);
glBufferData(GL_ARRAY_BUFFER, 9*sizeof(GLfloat), vertices2, GL_STATIC_DRAW);
glVertexAttribPointer((GLuint)0, 3, GL_FLOAT, GL_FALSE, 0, 0);
glEnableVertexAttribArray(0);
glBindVertexArray(0);
}
void initShaders(void)
{
GLuint p, f, v;
char *vs,*fs;
v = glCreateShader(GL_VERTEX_SHADER);
f = glCreateShader(GL_FRAGMENT_SHADER);
// load shaders & get length of each
GLint vlen;
GLint flen;
vs = loadFile("minimal.vert",vlen);
fs = loadFile("minimal.frag",flen);
const char * vv = vs;
const char * ff = fs;
glShaderSource(v, 1, &vv,&vlen);
glShaderSource(f, 1, &ff,&flen);
GLint compiled;
glCompileShader(v);
glGetShaderiv(v, GL_COMPILE_STATUS, &compiled);
if (!compiled)
{
cout << "Vertex shader not compiled." << endl;
printShaderInfoLog(v);
}
glCompileShader(f);
glGetShaderiv(f, GL_COMPILE_STATUS, &compiled);
if (!compiled)
{
cout << "Fragment shader not compiled." << endl;
printShaderInfoLog(f);
}
p = glCreateProgram();
glBindAttribLocation(p,0, "in_Position");
glBindAttribLocation(p,1, "in_Color");
glAttachShader(p,v);
glAttachShader(p,f);
glLinkProgram(p);
glUseProgram(p);
delete [] vs; // dont forget to free allocated memory
delete [] fs; // we allocated this in the loadFile function...
}
void display(void)
{
// clear the screen
glClear(GL_COLOR_BUFFER_BIT);
glBindVertexArray(vertexArrayObjID[0]); // First VAO
glDrawArrays(GL_TRIANGLES, 0, 3); // draw first object
glBindVertexArray(vertexArrayObjID[1]); // select second VAO
glVertexAttrib3f((GLuint)1, 1.0, 0.0, 0.0); // set constant color attribute
glDrawArrays(GL_TRIANGLES, 0, 3); // draw second object
glBindVertexArray(0);
glutSwapBuffers();
}
void reshape(int w, int h)
{
glViewport(0,0,(GLsizei)w,(GLsizei)h);
}
int main (int argc, char* argv[])
{
glutInit(&argc, argv);
glutInitDisplayMode(GLUT_DOUBLE | GLUT_RGBA);
glutInitWindowSize(600,600);
glutCreateWindow("Triangle Test");
glewInit();
GLenum err = glewInit();
if (GLEW_OK != err)
{
/* Problem: glewInit failed, something is seriously wrong. */
cout << "glewInit failed, aborting." << endl;
exit (1);
}
cout << "Status: Using GLEW " << glewGetString(GLEW_VERSION) << endl;
cout << "OpenGL version " << glGetString(GL_VERSION) << " supported" << endl;
init();
initShaders();
glutDisplayFunc(display);
glutReshapeFunc(reshape);
glutMainLoop();
return 0;
}
@kcsaff

Thanks, this was really helpful -- I spent some time looking for a Linux GLEW hello world and this worked immediately.

Sign up for free to join this conversation on GitHub. Already have an account? Sign in to comment
Something went wrong with that request. Please try again.