ios - Background color for drawing CIImage -

i use of cifilters image processing. i've found uiimageview slow display output image in real-time. i've followed documentation , built glkview. performance perfect, image rendered in black rect when rotated.

how set color background (green in case) or transparent?

here drawing code snippet. i'm not familiar graphics domain @ all.

private class imageview: glkview {      override init!(frame: cgrect, context: eaglcontext!) { // called `.opengles3` context.         cicontext = cicontext(eaglcontext: context, options: [kcicontextworkingcolorspace: nsnull()])         super.init(frame: frame, context: context)         }      private let cicontext: cicontext      private var image: ciimage? {         didset {             setneedsdisplay()         }     }      private override func drawrect(rect: cgrect) {          // clear `glclear`... here set color `backgroundcolor` (green) , cleared it.          if image != nil {                             cicontext.drawimage(image!, inrect: { /* returned computed rect */ }(), fromrect: image!.extent())         }     }      private override func layoutsubviews() {         super.layoutsubviews()         setneedsdisplay()     } } 

are setting blend mode?

glenable(gl_blend); glblendfunc(gl_src_alpha, gl_one_minus_src_alpha); glblendequation(gl_func_add); 

check link show visual effects of blend mode

if setting blend mode can show more of going on in drawrect method?