CODEWITHSUNDEEP
c++macosopengl
Peregrin
Peregrin

Reputation: 436

Why glDrawArrays doesn't draw with OpenGL on mac

I'm new to OpenGL and I can't figure out why nothing is displayed in the window. I'm using Mavericks (OS X 10.9.5) and there should be something missing I guess

#include <SFML/Window.hpp>
#include <SFML/OpenGL.hpp>
#include "FirstTriangleExample.h"

static const GLfloat g_vertex_buffer_data[] = {
        -1.0f, -1.0f, 0.0f,
        1.0f, -1.0f, 0.0f,
        0.0f,  1.0f, 0.0f,
};

GLuint vertexbuffer;
GLuint VertexArrayID;

void FirstTriangleExample::init() {
    glClearColor(0.0f, 0.0f, 0.4f, 0.0f);

    glGenVertexArraysAPPLE(1, &VertexArrayID);
    glBindVertexArrayAPPLE(VertexArrayID);

    glGenBuffers(1, &vertexbuffer);
    glBindBuffer(GL_ARRAY_BUFFER, vertexbuffer);
    glBufferData(GL_ARRAY_BUFFER, sizeof(g_vertex_buffer_data), g_vertex_buffer_data, GL_STATIC_DRAW);
}

// called in loop
void FirstTriangleExample::update() {
    glClear( GL_COLOR_BUFFER_BIT );

    glEnableVertexAttribArray(0);
    glBindBuffer(GL_ARRAY_BUFFER, vertexbuffer);
    glVertexAttribPointer(0, 3, GL_FLOAT, GL_FALSE, 0, (void*)0);

    glDrawArrays(GL_TRIANGLES, 0, 3);

    glDisableVertexAttribArray(0);

    glFlush();
}

void FirstTriangleExample::dispose() {
    glDeleteBuffers(1, &vertexbuffer);
    glDeleteVertexArraysAPPLE(1, &VertexArrayID);
    glDeleteProgram(programID);
}

with the example below everything works fine(I see the red square)

#include "RedSquareExample.h"
#include <SFML/OpenGL.hpp>

void RedSquareExample::init() {}

void RedSquareExample::update() {
    glClear(GL_COLOR_BUFFER_BIT | GL_DEPTH_BUFFER_BIT);
    glClearColor(0.0f, 0.0f, 0.0f, 1.0f); 
    glClear(GL_COLOR_BUFFER_BIT); 

    glBegin(GL_QUADS);
    glColor3f(0.0f, 1.0f, 0.0f);
    glVertex2f(-0.5f, -0.5f);
    glVertex2f( 0.5f, -0.5f);
    glVertex2f( 0.5f,  0.5f);
    glVertex2f(-0.5f,  0.5f);
    glEnd();

    glFlush();
}

void RedSquareExample::dispose() {}

Maybe the problem is in using APPLE extension (glGenVertexArraysAPPLE() and glBindVertexArrayAPPLE())?

Upvotes: 3

Views: 675

Answers (1)

BDL
BDL

Reputation: 22167

As far as I see from your code, you are using the fixed function pipeline. But this code:

glEnableVertexAttribArray(0);
glBindBuffer(GL_ARRAY_BUFFER, vertexbuffer);
glVertexAttribPointer(0, 3, GL_FLOAT, GL_FALSE, 0, (void*)0);

is only supposed to work when using shaders. In case of fixed function, you might want to use something like

glEnableClientState(GL_VERTEX_ARRAY);
glVertexPointer(3, GL_FLOAT, 0, (void*)0);

In addition, you are not using the VAO correctly. The purpose of a VAO is to store the bindings of buffers to attributes, but you reset the binding in your update method anyhow.

Upvotes: 3

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