android - GLES2.0+ framebuffer fade artifacts -

i'm writing simple test program on android using gles 2.0 or 3.0. (if solution works on 1 on other, that's i'll go with.)

problem:

• basically running strange pixel artifacts when fading colors.
• the problem can "hidden" making cutoff threshold higher fade still has patchy consistency , purpose not work.

example:

• example pictures (sorry, cant post images directly yet)
• the frame buffers resolution has been lowered make artifacts more visible.
• this issue occurs on devices tested (nexus 7 2012 , 2013, galaxy tab s 8.4, galaxy s6 edge, galaxy note 4)
• on newer devices, problem seems small pink uniform dots, on older devices seems patchy seen in linked pictures.
• running blur pass on final render out of question needs power efficient , mobile friendly.

layout:

• i create 2 frame buffers. (using gles20.gl_unsigned_short_5_6_5 format.)
• i set first 1 render target.
• i draw quad size of buffer framebuffer.
• the quads fragment shader setup render black dot moves in circle.
• the quad can take texture , blend dot.
• i switch rendering screen.
• i render quad using set render target texture.
• this process repeated each frame switching textures.

render code:

int = 0; @override public void ondrawview() {     setrendertarget(mrendertexture[i]);     mtestshader.settexture0(mrendertexture[(i + 1) % 2].gettexturehandle());     mtestshader.draw(mblitquad);     setrendertarget(null);     mblitshader.settexture0(mrendertexture[i].gettexturehandle());     mblitshader.draw(mblitquad);     = ++i % 2; } 

shader code:

precision highp float;  uniform float u_globaltime; uniform vec3 u_resolution; uniform sampler2d u_texture0;  varying vec2 v_texcoord;  void main(void) {     vec2 uv = v_texcoord * 2.0 - 1.0;     uv.x *= u_resolution.z;     vec2 pos = vec2(cos(u_globaltime), sin(u_globaltime)) * 0.5;     vec4 circle = vec4(1.0 - smoothstep(0.09, 0.11, length(pos - uv)));     vec4 px = max(texture2d(u_texture0, v_texcoord), circle) - 0.025;     gl_fragcolor = step(0.15, px) * px; } 

any on issue?

edit:
after googling on dither jerem, found gles20.gldisable(gles20.gl_dither). helps alot problem , on newer devices works perfect. on older devices i'm still running artifacting seen here.

edit2:
after more testing, switching buffer format rgb colors seems have done trick gles30.gl_unsigned_short_5_5_5_1. guess had how gpu compresses framebuffer green more noticeable. (it still helpful know specific reason why doesn't 5_6_5 format.)
final result after both fixes applied: i.imgur.com/bqsg9yj.png.

its multi-part solution, call gles20.gldisable(gles20.gl_dither), set render buffer format gles30.gl_unsigned_short_5_5_5_1, , jerem said, may able better results alpha disabled, though experimentation on device selection appeared have no effect, possible on other devices would.