# OpenGL glDrawArrays crashing when more than 4 vertices are provided

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Hey, just starting to work with openGL so I might be making a very stupid mistake. I'm using glDrawArrays and glVertexAttribPointer to draw primitives from an array that has 4 vertex position/vertex color pairs.

The shaders are very simple and just multiply the positions with the positions and pass the colors.

Now, everything works fine when I use 4 vertices or less. (3 draw a triangle and 2 draw nothing, as expected) But if I try to put 5 vertex/color pairs in vertex_data I get a crash with EXC_BAD_ACCESS

Here's the code which I think contains the problem:

[code]
const GLfloat vertex_data[] = {
-3.0f, 3.0f, 3.0f,
0.0f, 1.0f, 0.0f,
3.0f, 3.0f, 3.0f,
1.0f, 0.0f, 0.0f,
3.0f, 3.0f, -3.0f,
1.0f, 0.0f, 1.0f,
-3.0f, 3.0f, -3.0f,
1.0f, 1.0f, 0.0f,
//3.0f, 3.0f, 0.0f,
//1.0f, 0.0f, 0.0f, it crashes if I uncomment these lines
};

void render() {
glClearColor(0.2f, 0.2f, 0.2f, 0.0f);
glClear(GL_COLOR_BUFFER_BIT);

glUseProgram(program);

glBindBuffer(GL_ARRAY_BUFFER, position_buffer);

glEnableVertexAttribArray(glGetAttribLocation(program, "position"));
glVertexAttribPointer(glGetAttribLocation(program, "position"), sizeof(vertex_data)/(sizeof(GLfloat)*6), GL_FLOAT, GL_FALSE, sizeof(GLfloat)*6, (void*)0);

glEnableVertexAttribArray(glGetAttribLocation(program, "color"));
glVertexAttribPointer(glGetAttribLocation(program, "color"), sizeof(vertex_data)/(sizeof(GLfloat)*6), GL_FLOAT, GL_FALSE, sizeof(GLfloat)*6, (void*)(sizeof(GLfloat)*3));

glUniformMatrix4fv(glGetUniformLocation(program, "perspective"), 1, GL_TRUE, perspective);
glUniformMatrix4fv(glGetUniformLocation(program, "transform"), 1, GL_TRUE, transform);

//Here is where it crashes with EXC_BAD_ACCESS if I have more than 4 vertices
glDrawArrays(GL_TRIANGLE_STRIP, 0, sizeof(vertex_data)/(sizeof(GLfloat)*6));

glBindBuffer(GL_ARRAY_BUFFER, 0);
glDisableVertexAttribArray(0);
glUseProgram(0);

glutSwapBuffers();
}
[/code]

I tried using GL_QUADS, GL_TRIANGLES and GL_TRIANGLE_STRIP, nothing works with more than 4 vertices.

Here is all the initialization:

[code]
glutInit(&argc, argv);

position_buffer = 0;

glutInitDisplayMode(GLUT_RGBA | GLUT_DOUBLE);
glutInitWindowSize(800, 600);

glutCreateWindow("GLUT Window");

glutIdleFunc(&update);
glutDisplayFunc(&render);
glutReshapeFunc(&reshape);
glutSpecialFunc(&keyboard);
glutSpecialUpFunc(&keyboard_up);
glGenBuffers(1, &position_buffer);

glBindBuffer(GL_ARRAY_BUFFER, position_buffer);
glBufferData(GL_ARRAY_BUFFER, sizeof(vertex_data), vertex_data, GL_STATIC_DRAW);
glBindBuffer(GL_ARRAY_BUFFER, 0);
[/code]

I can't get the debugger to give me any meaningful information and what's really bothering me is that it does work with 4 vertices or less. I think I provided all the necessary information, but if I'm missing something let me know.

I'm absolutely stumped, all help is appreciated.

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Check your second argument to glVertexAttribPointer, I think you have misinterpreted it.

[quote]
size
Specifies the number of components per generic vertex attribute. Must be 1, 2, 3, or 4. The initial value is 4.
[/quote]

You appear to be passing in the number of vertices, when in your case this should just be a fixed '3'.

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[quote name='karwosts' timestamp='1297980567' post='4775606']
Check your second argument to glVertexAttribPointer, I think you have misinterpreted it.

[quote]
size
Specifies the number of components per generic vertex attribute. Must be 1, 2, 3, or 4. The initial value is 4.
[/quote]

You appear to be passing in the number of vertices, when in your case this should just be a fixed '3'.
[/quote]

[url="http://thinkexist.com/quotation/may_flowers_always_line_your_path_and_sunshine/151623.html"][/url]May flowers always line your path and sunshine light your day, that was exactly it. Thanks a lot, man!

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