float radius = 0.5;
    vec2 center = vec2(0.5f,0.5f);
    float circle = radius * radius;
    float rx = center.x * wh_ratio;
    float ry = center.y;
    float dis = (v_textCoords.x * wh_ratio - rx) * (v_textCoords.x * wh_ratio - rx) + (v_textCoords.y  - ry) * (v_textCoords.y - ry);

    textColor.a = smoothstep(circle,circle-0.001 ,dis);
    gl_FragColor = textColor;

89051ee3535242aa6201a18c8e67b077.png