Opengl will not display anything - c++

Question

I'm trying to get a small triangle to display.
Here is my initialization code:
void PlayerInit(Player P1)
{
glewExperimental = GL_TRUE;
glewInit();
//initialize buffers needed to draw the player
GLuint vao;
GLuint buffer;
glGenVertexArrays(1, &vao);
glGenBuffers(1, &buffer);
//bind the buffer and vertex objects
glBindVertexArray(vao);
glBindBuffer(GL_ARRAY_BUFFER, buffer);
//Set up a buffer to hold 6 floats for position, and 9 floats for color
glBufferData(GL_ARRAY_BUFFER, sizeof(float)*18, NULL, GL_STATIC_DRAW);
//push the vertices of the player into the buffer
glBufferSubData(GL_ARRAY_BUFFER, 0, sizeof(float)*9, CalcPlayerPoints(P1.GetPosition()));
//push the color of each player vertex into the buffer
glBufferSubData(GL_ARRAY_BUFFER, sizeof(float)*9, sizeof(float)*9, CalcPlayerColor(1));
//create and compile the vertex/fragment shader objects
GLuint vs = create_shader("vshader.glsl" ,GL_VERTEX_SHADER);
GLuint fs = create_shader("fshader.glsl" ,GL_FRAGMENT_SHADER);
//create a program object and link the shaders
GLuint program = glCreateProgram();
glAttachShader(program, vs);
glAttachShader(program, fs);
glLinkProgram(program);
//error checking for linking
GLint linked;
glGetProgramiv(program, GL_LINK_STATUS, &linked);
if(!linked)
{
std::cerr<< "Shader program failed to link" <<std::endl;
GLint logSize;
glGetProgramiv(program, GL_INFO_LOG_LENGTH, &logSize);
char* logMsg = new char[logSize];
glGetProgramInfoLog(program, logSize, NULL, logMsg);
std::cerr<< logMsg << std::endl;
delete [] logMsg;
exit(EXIT_FAILURE);
}
glUseProgram(program);
//create attributes for color and position to pass to shaders
//enable each attribute
GLuint Pos = glGetAttribLocation( program, "vPosition");
glEnableVertexAttribArray(Pos);
GLuint Col = glGetAttribLocation( program, "vColor");
glEnableVertexAttribArray(Col);
//set a pointer at the proper offset into the buffer for each attribute
glVertexAttribPointer(Pos, 3, GL_FLOAT, GL_FALSE, 0, (const GLvoid*) (sizeof(float)*0));
glVertexAttribPointer(Col, 3, GL_FLOAT, GL_FALSE, 0, (const GLvoid*) (sizeof(float)*9));
}
I don't have much experience writing shader linkers, so I think that is where the problem might be. I have some error checking in the shader loader, and nothing comes up. So I think that is fine.
Next I have my display and main function:
//display function for the game
void GameDisplay( void )
{
//set the background color
glClearColor(1.0, 0.0, 1.0, 1.0);
//clear the screen
glClear(GL_COLOR_BUFFER_BIT);
//Draw the Player
glDrawArrays(GL_TRIANGLES, 0, 3);
glutSwapBuffers();
}
//main function
int main(int argc, char** argv)
{
glutInit(&argc, argv);
glutInitDisplayMode(GLUT_RGBA | GLUT_DOUBLE);
glutInitWindowSize(500, 500);
glutCreateWindow("Asteroids");
Player P1 = Player(0.0, 0.0);
PlayerInit(P1);
glutDisplayFunc(GameDisplay);
glutMainLoop();
return 0;
}
Vertex shader :
attribute vec3 vPosition;
attribute vec3 vColor;
varying vec4 color;
void main()
{
color = vec4(vColor, 1.0);
gl_Position = vec4(vPosition, 1.0);
}
Fragment shader
varying vec4 color;
void main()
{
gl_FragColor = color;
}
That's all of the relevant code. CalcPlayerPoints just returns a float array of size 9 to hold the triangle coordinates. CalcPlayerColor does something similar.
One last problem that may help with diagnosing the problem is that whenever I try to exit the program by closing the window of the application, I get a breakpoint in the glutmainloop, however if I close the console window, it exits fine.
Edit: I added the shaders for reference.
Edit: I am using opengl version 3.1

Answer 1

Without the shaders, we can't say if the faulty code isn't GLSL (bad vertices transformations, etc.)
Have you tried checking glGetError to see if the problem doesn't come from your initialization code ?
Maybe try to set the output of your fragment shader to, say, vec4(1.0, 0.0, 0.0, 1.0) to check if its normal output is ill-formed.
Your last problem seems to unveil an undefined behavior, like bad memory allocation/deallocation, which may take place in your Player class (by the way consider passing the object as a reference in your initialization code, because it may at the moment trigger a shallow copy and then a double-free of some pointer).

Answer 2

Turns out there was something wrong with how I was returning the array of vertices from the function used to compute them. The rest of the code worked fine after that fix.