I’m trying to run a program using shaders. In Another question I made, I discovered that I was mixing the fixed pipeline functions with the newer stuff (from OpenGL 2.0), so I tried to remove all the “old stuff” like glMatrixMode, but I’m not sure if I’m doing it correctly. In the doubt I also removed calls like glLightfv which I’m not really sure if they’re allowed if I used a programmable pipeline.
This is the main code:
#include <GL/glew.h>
#include <GL/glut.h>
#include <iostream>
#include <vector>
#include "utility.hpp"
#include "program.hpp"
GLfloat width=600, height=800;
Program* program_ref;
void init()
{
glewInit();
Shader vertex_shader= Shader("vertex_shader",GL_VERTEX_SHADER);
// This just reads the file "vertex_shader", creates the shader and compiles it
Shader geometry_shader= Shader(); // This means that the shader is empty
// So the program class will be enough smart to recognize it and don't attach it
Shader fragment_shader= Shader("fragment_shader",GL_FRAGMENT_SHADER);
program_ref= new Program(vertex_shader,geometry_shader,fragment_shader);
// This creates a program, attaches the shaders to it, links and uses it
}
void display()
{
vector<GLfloat> quad{-0.5,-0.5,0.5,-0.5,0.5,0.5,-0.5,0.5};
glClearColor(0,0,0,0);
glClear(GL_COLOR_BUFFER_BIT);
glEnableClientState(GL_VERTEX_ARRAY);
glVertexPointer(2,GL_FLOAT,0,quad.data());
glDrawArrays(GL_QUADS,0,4);
glDisableClientState(GL_VERTEX_ARRAY);
glutSwapBuffers();
cout << glGetError() << endl;
}
void reshape(int w, int h)
{
width=w;
height=h;
glutPostRedisplay();
}
int main(int argc, char** argv)
{
glutInit(&argc, argv);
glutInitDisplayMode(GLUT_RGB | GLUT_DOUBLE);
glutInitWindowPosition(100,100);
glutInitWindowSize(500,500);
glutCreateWindow("test");
glutDisplayFunc(display);
glutReshapeFunc(reshape);
init();
glewInit();
glutMainLoop();
return 0;
}
(Optional classes to see, in the comments I wrote how are Program and Shader are behaving)
shader.hpp:
#ifndef shader_hpp
#define shader_hpp
#include "utility.hpp"
#include "shader.hpp"
#include <fstream>
#define MAX_SIZE (size_t)1.0e5
class Shader
{
private:
GLuint id;
GLenum type;
bool null;
public:
Shader()
{
id=-1;
type= -1;
null= true;
}
Shader(const string& filename,GLenum type)
{
GLchar* data= new GLchar[MAX_SIZE];
streamsize count;
this->type= type;
ifstream is;
is.open(filename);
is.read(data,MAX_SIZE);
count= is.gcount();
is.close();
id=glCreateShader(type);
glShaderSource(id,1,(const GLchar**)&data,&count);
glCompileShader(id);
delete[] data;
null= false;
}
GLuint getId() const
{
return id;
}
GLenum getType() const
{
return type;
}
bool isNull() const
{
return null;
}
};
#endif
program.hpp:
#ifndef program_hpp
#define program_hpp
#include "utility.hpp"
#include "shader.hpp"
class Program
{
private:
GLuint id;
public:
Program(const Shader& vertex_shader, const Shader& geometry_shader, const Shader& fragment_shader)
{
id= glCreateProgram();
if(!vertex_shader.isNull())
{
glAttachShader(id,vertex_shader.getId());
}
if(!geometry_shader.isNull())
{
glAttachShader(id,geometry_shader.getId());
}
if(!fragment_shader.isNull())
{
glAttachShader(id,fragment_shader.getId());
}
glLinkProgram(id);
glUseProgram(id);
}
GLuint getId()
{
return id;
}
};
#endif
There two classes are just made to simplify everything when using glew to compile the shaders and attach them to the program.
The problem is the following: If I just attach the vertex shader and not the fragment shader, all is fine and I see the quad drawn with the right color (red, because in the vertex shader below I’ll set the color to red). If instead I also attach the fragment shader I see that the quad is white. I also tried to see what wasn’t right and I printed the result of glGetError(). If I include the fragment shader I get error 1282, if I don’t include it I don’t get any error (0).
Vertex shader:
void main()
{
gl_Position = gl_ModelViewProjectionMatrix * gl_Vertex;
gl_FrontColor = vec4(1,0,0,1);
// The only relevant thing I do is to set the color to red
// I see the quad red if I attach only the vertex shader and not the fragment shader
gl_TexCoord[0] = gl_MultiTexCoord0;
}
Fragment shader:
void main()
{
gl_fragColor= gl_Color;
}
Give this a shot:
As Antonie Blom pointed out
gl_fragColorshould begl_FragColor. The lower-casefchokes the GLSL compiler on my system.