OpenglES alpha texture depth

Question

glClear( GL_COLOR_BUFFER_BIT |GL_DEPTH_BUFFER_BIT );

glUseProgram(_program);
GLKVector2 poz= { 0, 0};
if (_Sprite2)
{
    float aspect = ( GLfloat ) _screenWidth/ ( GLfloat ) _screenHeight;
    [self esMatrixLoadIdentity : &perspective];
    [self esPerspective:&perspective pos_fovy:60.0f pos_aspect:aspect  pos_nearZ:1.0f pos_farZ:30.0f];


    [self esMatrixLoadIdentity : &modelview];
    [self esTranslate : &modelview trans_x:0.0f trans_y:-0.5f trans_z:-5 ];
    [self esRotate : &modelview gl_angle:0.0f _x:1.0 _y:0.0 _z:1.0];
    [self esMatrixMultiply :&mvpMatrix src_A:&modelview src_B:&perspective];

    glUniformMatrix4fv ( mvpLoc, 1, GL_FALSE, (GLfloat*) &mvpMatrix.m[0][0] );

    [_Sprite2 update : poz];
    [_Sprite2 draw];
}/// crown

if(_sprite)//bug
{
    float aspect = ( GLfloat ) _screenWidth/ ( GLfloat ) _screenHeight;
    [self esMatrixLoadIdentity : &perspective];
    [self esPerspective:&perspective pos_fovy:60.0f pos_aspect:aspect  pos_nearZ:1.0f pos_farZ:30.0f];

    [self esMatrixLoadIdentity : &modelview];
    [self esTranslate : &modelview trans_x:0.0f trans_y:0.0f trans_z:_zPoz + _zPoz_2];
    [self esRotate : &modelview gl_angle:0.0f _x:1.0 _y:0.0 _z:1.0];

    [self esMatrixMultiply :&mvpMatrix src_A:&modelview src_B:&perspective];

    glUniformMatrix4fv ( mvpLoc, 1, GL_FALSE, (GLfloat*) &mvpMatrix.m[0][0] );

    [_sprite update : poz];
    [_sprite draw];
}

Bug image changes depth-z, and crown's transparency region is now working correctly.

How can I see behind bug correctly?

Answer 1

You need to either:

1. Sort your sprites so they render back-to-front without depth testing, and just rely on blending to provide transparencies.
2. Add an alpha test to your fragment shader to drop fragments which are transparent (eg if (alpha < 0.05) discard; , adjust transparency threshold as appropriate)