OpenGL to OpenGL-ES - Changing color of triangles in a strip

Question

When using glBegin() and glEnd() in opengl you are able to set and change the color between each glVertex3f(). How can you recreate this behavior when using a vertex array and glDrawArrays(). Here it is in regular opengl.

for(angle = 0.0f; angle < (2.0f*GL_PI); angle += (GL_PI/8.0f))
    {
    // Calculate x and y position of the next vertex
    x = 50.0f*sin(angle);
    y = 50.0f*cos(angle);

    // Alternate color between red and green
    if((iPivot %2) == 0)
        glColor3f(0.0f, 1.0f, 0.0f);
    else
        glColor3f(1.0f, 0.0f, 0.0f);

    // Increment pivot to change color next time
    iPivot++;

    // Specify the next vertex for the triangle fan
    glVertex2f(x, y);
    }

Answer 1

With glDrawArrays you have to enable the glVertexPointer to set the vertex data.

In the same way you can also set a client-memory pointer for the colors.

It boils down to these calls:

  glEnableClientState (GL_VERTEX_ARRAY);
  glEnableClientState (GL_COLOR_ARRAY); // enables the color-array.

  glVertexPointer (...  // set your vertex-coordinates here..
  glColorPointer (...   // set your color-coorinates here..

  glDrawArrays (... // draw your triangles

Btw - texture-coordinates are handled in the same way. Just use GL_TEXCOORD_ARRAY and glTexCoordPointer for this.