OpenGL ES 2.0 iOS zero alpha pixel creating opaque color -

i clear framebuffer...

glclearcolor(0.0, 0.0, 0.0, 0.0); glclear(gl_color_buffer_bit);

...i enable blending such...

glenable(gl_blend); glblendfunc(gl_one, gl_one_minus_src_alpha); [self render] gldisable(gl_blend);

in render code, add quad , draw it. in fragment shader have...

gl_fragcolor = vec4(0.0, 0.0, 0.0, 0.0);

this yields clear quad. great. no color, no alpha, no nothing...got it. however, change fragment shader to...

gl_fragcolor = vec4(1.0, 0.0, 0.0, 0.0);

i quad filled white. can explain me how filling quad transparent red yield opaque white, , not clear?

doesn't gl_one_minus_src_alpha do

(1, 1, 1, 1) - (as/ka, as/ka, as/ka, as/ka)

so if 0 result in (1, 1, 1, 1)?

ed though i'm not clear why has different effect when set fragment (1, 0, 0, 0) (0, 0, 0, 0). notice used

glblendfunc(gl_src_alpha, gl_one_minus_src_alpha)

what different arguments blend function?

UV code