Pro OpenGL ES for iOS

234 CHAPTER 7: Well-Rendered Miscellany^

O K , t a k e a d e e p b r e a t h -----we have more to cover. Listing 7-13 demonstrates the new

drawLight() routine, while Listing 7-14 demonstrates drawPlatform(). The meat of the

exercise is Listing 7-15, calculating the shadow’s matrix, and Listing 7-16, drawing the

shadow. Are you tingling yet? I know I am.

Listing 7-13. The modified drawLight() routine

-(void)drawLight:(int)lightNumber

{

static GLbyte lampVertices[]={0,0,0}; //1

glDisableClientState(GL_COLOR_ARRAY);

glEnable(GL_POINT_SMOOTH); //2

glPointSize(5.0); //3

glLightfv(lightNumber, GL_POSITION, iLightPos ); //4

glPushMatrix();

glRotatef(m_WorldRotationX, 1.0, 0.0, 0.0); //5

glRotatef(m_WorldRotationY, 0.0, 1.0, 0.0);

glTranslatef( iLightPosX, iLightPosY, iLightPosZ ); //6

glColor4f( 1.0, 1.0, 0, 1.0); //7

glVertexPointer( 3, GL_BYTE, 0, lampVertices ); //8

glDrawArrays(GL_POINTS, 0,1);

glPopMatrix();

glEnableClientState(GL_COLOR_ARRAY);

}

The preceding code will draw a round dot to the screen, showing where the light source

is located at any moment.

„ Since we want only a single point to draw, we can specify a single

vertex at the origin in line 1.

„ GL_POINT_SMOOTH is something new. It tells OpenGL that any points it

draws should be round. Without this, the light would be rendered as a

square.

„ Line 3 is another new call that tells the system that the point is to be 5

pixels across. The maximum size can vary on different devices but can

typically go up to 64 or 128 pixels in diameter.

„ Now we can set the absolute position of the actual light here in line 4.

„ Lines 5ff rotate the lamp in world space, while line 6 translates it.

„ The color is set to yellow via line 7, while lines 8ff supply the vertex

and then draw it via glDrawArrays().

But wait, there’s more!