Added stencil buffer support on iOS.

Thanks to Brian Barnes for the initial work on this patch!

src/video/uikit/SDL_uikitopengles.m

@@ -112,6 +112,7 @@ SDL_GLContext UIKit_GL_CreateContext(_THIS, SDL_Window * window)
                                     bBits: _this->gl_config.blue_size
                                     aBits: _this->gl_config.alpha_size
                                     depthBits: _this->gl_config.depth_size
+                                    stencilBits: _this->gl_config.stencil_size
                                     majorVersion: _this->gl_config.major_version];
 
     data->view = view;

src/video/uikit/SDL_uikitopenglview.h

@@ -60,6 +60,7 @@
     bBits:(int)bBits
     aBits:(int)aBits
     depthBits:(int)depthBits
+    stencilBits:(int)stencilBits
     majorVersion:(int)majorVersion;
 
 - (void)updateFrame;

src/video/uikit/SDL_uikitopenglview.m

@@ -40,10 +40,12 @@
       bBits:(int)bBits
       aBits:(int)aBits
       depthBits:(int)depthBits
+      stencilBits:(int)stencilBits
       majorVersion:(int)majorVersion
 {
+    const BOOL useStencilBuffer = (stencilBits != 0);
+    const BOOL useDepthBuffer = (depthBits != 0);
     NSString *colorFormat = nil;
-    BOOL useDepthBuffer;
 
     if (rBits == 8 && gBits == 8 && bBits == 8) {
         /* if user specifically requests rbg888 or some color format higher than 16bpp */
@@ -56,22 +58,19 @@
 
     depthBufferFormat = 0;
 
+    if (useDepthBuffer) {
         if (depthBits == 24) {
-        useDepthBuffer = YES;
             depthBufferFormat = GL_DEPTH_COMPONENT24_OES;
         }
-    else if (depthBits == 0) {
-        useDepthBuffer = NO;
-    }
         else {
             /* default case when depth buffer is not disabled */
             /*
                strange, even when we use this, we seem to get a 24 bit depth buffer on iPhone.
                perhaps that's the only depth format iPhone actually supports
             */
-        useDepthBuffer = YES;
             depthBufferFormat = GL_DEPTH_COMPONENT16_OES;
         }
+    }
 
     if ((self = [super initWithFrame:frame])) {
         // Get the layer
@@ -103,12 +102,22 @@
         glGetRenderbufferParameterivOES(GL_RENDERBUFFER_OES, GL_RENDERBUFFER_WIDTH_OES, &backingWidth);
         glGetRenderbufferParameterivOES(GL_RENDERBUFFER_OES, GL_RENDERBUFFER_HEIGHT_OES, &backingHeight);
 
-        if (useDepthBuffer) {
+        if ((useDepthBuffer) || (useStencilBuffer)) {
+            if (useStencilBuffer) {
+                // Apparently you need to pack stencil and depth into one buffer.
+                // !!! FIXME: this is the only thing (currently) supported. May not always be true.
+                depthBufferFormat = GL_DEPTH24_STENCIL8_OES;
+            }
             glGenRenderbuffersOES(1, &depthRenderbuffer);
             glBindRenderbufferOES(GL_RENDERBUFFER_OES, depthRenderbuffer);
             glRenderbufferStorageOES(GL_RENDERBUFFER_OES, depthBufferFormat, backingWidth, backingHeight);
+            if (useDepthBuffer) {
                 glFramebufferRenderbufferOES(GL_FRAMEBUFFER_OES, GL_DEPTH_ATTACHMENT_OES, GL_RENDERBUFFER_OES, depthRenderbuffer);
             }
+            if (useStencilBuffer) {
+                glFramebufferRenderbufferOES(GL_FRAMEBUFFER_OES, GL_STENCIL_ATTACHMENT_OES, GL_RENDERBUFFER_OES, depthRenderbuffer);
+            }
+        }
 
         if (glCheckFramebufferStatusOES(GL_FRAMEBUFFER_OES) != GL_FRAMEBUFFER_COMPLETE_OES) {
             return NO;