Question

I’m trying to learn OpenGL. I tried some code I found in this book but the output of the program is just a white screen, the output should be the Sierpinski triangle.

What could be wrong? I’m developing on Mac OS X 10.8 and Xcode 4.5

#include "Angel.h"
#include <iostream>

const int numPoints = 5000;
typedef vec2 point2;

void init(){

    point2 points[numPoints];
    point2 vertices[3] = {
        point2(-1.0, -1.0), point2(0.0, 1.0), point2(1.0, -1.0)
    };

    points[0] = point2(0.25, 0.5);

    for (int k = 1; k < numPoints; k++) {
        int j = rand()%3;
        points[k] = (points[k-1]+vertices[j])/2.0;
    }

    GLuint program = InitShader("vertex.glsl", "fragment.glsl");
    glUseProgram(program);

    GLuint abuffer;
    glGenVertexArraysAPPLE(1, &abuffer);
    glBindVertexArrayAPPLE(abuffer);

    GLuint buffer;
    glGenBuffers(1, &buffer);
    glBindBuffer(GL_ARRAY_BUFFER, buffer);
    glBufferData(GL_ARRAY_BUFFER, sizeof(points), points, GL_STATIC_DRAW);

    GLuint location = glGetAttribLocation(program, "vPosition");
    glEnableVertexAttribArray(location);
    glVertexAttribPointer(location, 2, GL_FLOAT, GL_FALSE, 0, BUFFER_OFFSET(0));

    glClearColor(1.0, 1.0, 1.0, 1.0);

}


void display(){
    glClear(GL_COLOR_BUFFER_BIT);
    glDrawArrays(GL_POINTS, 0, numPoints);
    glFlush();
}

int main(int argc, char** argv){

    glutInit(&argc, argv);

    glutInitDisplayMode(GLUT_RGBA | GLUT_3_2_CORE_PROFILE);

    glutInitWindowSize(640, 480);

    glutCreateWindow("Sierpinski Gasket");

    init();

    glutDisplayFunc(display);

    glutMainLoop();

    return 0;
}

Answer 1

Finally !
The code is complete, the shaders are attached as they should be.

There’s a problem with a .h files included in Angel.h, instead of having <OpenGL/OpenGL.h> it should be <OpenGL/gl3.h>. The second thing to change is to remove the APPLE suffix to the functions glGenVertexArrayAPPLE and glBindVertexArrayAPPLE.

Apparently there’s a problem with Apple and their implementation of OpenGL, probably not all the stuff is compatible with what they have, but I let that topic to the experts, if there’s someone out there please clarify this.