Pro OpenGL ES for iOS

58 CHAPTER 3: Building a 3D World^

glVertexPointer(2, GL_FLOAT, 0, squareVertices); //13

glEnableClientState(GL_VERTEX_ARRAY);

glColorPointer(4, GL_UNSIGNED_BYTE, 0, squareColors);

glEnableClientState(GL_COLOR_ARRAY);

glDrawArrays(GL_TRIANGLE_STRIP, 0, 4); //14

if(!(counter%100)); //15

NSLog(@"FPS: %d\n",self.framesPerSecond);

counter++;

}

@end

You’ll recognize a number of similar elements here from Chapter 1, but in a more

compact form. All OpenGL ES 2 code has been removed for clarity.

„ Line 1 defines our viewcontroller as a subclass of GLKViewController

„ In line 2, the API is initialized, with OpenGL ES 1 as the chosen

approach, by passing it the kEAGLRenderingAPIOpenGLES1 flag. The

context is returned and fed to the GLKView.

„ Lines 3ff bind the context that was fetched in line 2. Then the current

context is set. Without that being set, OpenGL will fail on many calls

coming up.

„ The drawInRect() method in line 4 is a delegate call from

GLKViewController. All of the geometry and attributes are specified

here for clarity.

„ Line 5 creates an array of vertices. Because this a 2D demo without

lighting, only two values are needed for each vertex. Line 6 is our color

array, using the standard RGBA format. One color for each of the four

vertices.

„ Lines 7f are identical to the first exercise, filling in the background with

a medium gray.

„ Line 8 sets the current matrix to be a projection matrix, and line 9

initializes it with an ‘‘identity matrix.’’

„ Lines 10 and 11 do the same for the modelview.

„ Instead of generating a matrix of our own and modifying it directly, as

in Chapter 1, ES 1 handles those kind of housekeeping chores for us.

So here in line 12, glTranslatef() moves the square along only the Z-

axis (hence the middle value) using a sin function. Using a sin gives it a

nice smooth motion that slows up at either end.