Open GL - ES 2.0 : Drawing a simple line

Question

I have spent quite some time and effort trying to figure out how to draw a line in opneGL es on the iPhone. Here is my code

 myMagicVertices[0] = -0.5;
    myMagicVertices[1] = -0.5;
    myMagicVertices[2] = 2.0;
    myMagicVertices[3] = 2.0;

    glDrawElements(GL_LINE_STRIP, 2, GL_UNSIGNED_BYTE, myMagicVertices);

But all I see on the screen is a blank screen. I am at my wits end. Can any body point me to the right dirrection

Answer 1

the last argument of glDrawElements() should be a list of indices into your vertex list, not the vertices themselves. You also need to tell OpenGL about you list of vertices.

the code should look something like this:

float vertices[] = {-0.5f, -0.5f, 0.5f, 0.5f};
unsigned int indices[] = {0, 1};

glEnableClientState(GL_VERTEX_ARRAY);
glVertexPointer(2, GL_FLOAT, 0, vertices);
glDrawElements(GL_LINES, 2, GL_UNSIGNED_INT, indices);

edit: I think this would also work:

float vertices[] = {-0.5f, -0.5f, 0.5f, 0.5f};

glEnableClientState(GL_VERTEX_ARRAY);
glVertexPointer(2, GL_FLOAT, 0, vertices);

glDrawArrays(GL_LINES, 0, 2);