Pro OpenGL ES for iOS

222 CHAPTER 7: Well-Rendered Miscellany^

0.5, 0.0, -.5f,

-0.5, 0.0, 0.5,

0.5, 0.0, 0.5

};

static const GLubyte colors[] =

{

255, 0, 0, 128,

255, 0, 0, 255,

0, 0, 0, 0,

128, 0, 0, 128

};

glFrontFace(GL_CW);

glPushMatrix();

glTranslatef(0.0,-1.0,-3.0);

glScalef(2.5,1.5,2.0);

glVertexPointer(3, GL_FLOAT, 0, flatSquareVertices);

glEnableClientState(GL_VERTEX_ARRAY);

glColorPointer(4, GL_UNSIGNED_BYTE, 0, colors);

glDepthMask(GL_FALSE); //1

glColorMask(GL_TRUE, GL_FALSE, GL_FALSE, GL_TRUE); //2

glDrawArrays( GL_TRIANGLE_STRIP,0, 4); //3

glColorMask(GL_TRUE, GL_TRUE, GL_TRUE, GL_TRUE); //4

glDepthMask(GL_TRUE); //5

glPopMatrix();

}

„ In line 1, writing to the depth buffer is disabled, and line 2 disables the

green and blue color channels, so only the red one will be used. That

is how the reflected area gets its little red highlight.

„ Now we can draw the image to the stencil buffer in line 3.

„ Lines 4 and 5 reset the masks.

At this point, the drawInRect() routine has to be modified, yet again. Yawn.... And if you

can keep your peepers open, check out Listing 7-10 for the cruel and unvarnished truth.

Sorry for repeating so much of the previous code, but it’s much easier than saying

‘‘...and after the line about squirrel trebuchets add such-and-such a line....’’

Listing 7-10. The reflection drawInRect() method

• (void)glkView:(GLKView *)view drawInRect:(CGRect)rect
  {
  static GLfloat z=-3.0;
  static GLfloat spinX=0;
  static GLfloat spinY=0;