效果:

VSH:

#ifdef OPENGL_ES
precision mediump vec2;
precision mediump float;
#endif

// Attributes
attribute vec3 a_position;
attribute vec2 a_texCoord;
attribute vec4 a_color;

// Varyings
#ifdef GL_ES
varying vec2 v_texCoord;
#else
varying vec2 v_texCoord;
#endif
varying vec4 v_fragmentColor;

void main()
{
    gl_Position = CC_PMatrix * vec4(a_position,1.0);
    v_texCoord = a_texCoord;
    v_fragmentColor = a_color;
}

#ifdef GL_ES
precision mediump float;
#endif

varying vec2 v_texCoord;
varying vec4 v_fragmentColor;
void main() 
{
    vec4 col = texture2D(CC_Texture0,v_texCoord );
    float h = dot(col.rgb,vec3(0.3,0.59,0.21));
	gl_FragColor = vec4(h,h,col.a);
}