So I am trying to use a stencil buffer in iOS for masking/clipping purposes. Do you guys have any idea why this code may not work? This is everything I have associated with Stencils. On iOS 4 I get a black screen. On iOS 5 I get exactly what I expect. The transparent areas of the image I drew in the stencil are the only areas being drawn later.

Code is below.

This is where I setup the frameBuffer, depth and stencil. In iOS the depth and stencil are combined.

-(void)setupDepthBuffer
{
    glGenRenderbuffers(1, &depthRenderBuffer);
    glBindRenderbuffer(GL_RENDERBUFFER, depthRenderBuffer);
    glRenderbufferStorage(GL_RENDERBUFFER, GL_DEPTH24_STENCIL8_OES, self.frame.size.width * [[UIScreen mainScreen] scale], self.frame.size.height * [[UIScreen mainScreen] scale]);
}

-(void)setupFrameBuffer
{    
    glGenFramebuffers(1, &frameBuffer);
    glBindFramebuffer(GL_FRAMEBUFFER, frameBuffer);
    glFramebufferRenderbuffer(GL_FRAMEBUFFER, GL_COLOR_ATTACHMENT0, GL_RENDERBUFFER, colorRenderBuffer);
    glFramebufferRenderbuffer(GL_FRAMEBUFFER, GL_DEPTH_ATTACHMENT, GL_RENDERBUFFER, depthRenderBuffer);
    glFramebufferRenderbuffer(GL_FRAMEBUFFER, GL_STENCIL_ATTACHMENT, GL_RENDERBUFFER, depthRenderBuffer);

    // Check the FBO.
    if(glCheckFramebufferStatus(GL_FRAMEBUFFER) != GL_FRAMEBUFFER_COMPLETE) {
        NSLog(@"Failure with framebuffer generation: %d", glCheckFramebufferStatus(GL_FRAMEBUFFER));
    }
}

This is how I am setting up and drawing the stencil. (Shader code below.)

glEnable(GL_STENCIL_TEST);
glDisable(GL_DEPTH_TEST);
glColorMask(GL_FALSE, GL_FALSE, GL_FALSE, GL_FALSE);
glDepthMask(GL_FALSE);

glStencilFunc(GL_ALWAYS, 1, -1);
glStencilOp(GL_KEEP, GL_KEEP, GL_REPLACE);

glColorMask(0, 0, 0, 0);
glClear(GL_STENCIL_BUFFER_BIT);

machineForeground.shader = [StencilEffect sharedInstance];
[machineForeground draw];
machineForeground.shader = [BasicEffect sharedInstance];

glDisable(GL_STENCIL_TEST);
glColorMask(GL_TRUE, GL_TRUE, GL_TRUE, GL_TRUE);
glDepthMask(GL_TRUE);

Here is where I am using the stencil.

glEnable(GL_STENCIL_TEST);
glStencilOp(GL_KEEP, GL_KEEP, GL_KEEP);
glStencilFunc(GL_EQUAL, 1, -1);

...Draw Stuff here

glDisable(GL_STENCIL_TEST);

Finally here is my fragment shader.

varying lowp vec2 TexCoordOut;
uniform sampler2D Texture;

void main(void)
{
    lowp vec4 color = texture2D(Texture, TexCoordOut);

    if(color.a < 0.1)
        gl_FragColor = color;
    else
        discard;
}