对称

precision highp float;
varying lowp vec2 varyTextCoord;
uniform sampler2D texMap;
uniform sampler2D colorMap;
uniform float stepValue;

void main() {
    float uT = stepValue;
    vec2 st = varyTextCoord;
    vec3 color;
    
    if (st.x < 0.5) {
        st = vec2(st.x, st.y);
        vec3 thisrgb = texture2D(colorMap, vec2(1.0 - st.x, st.y)).rgb;;
        color = thisrgb;
    }else {
        st = vec2(st.x, st.y);
        vec3 thisrgb = texture2D(colorMap, vec2(st.x, st.y)).rgb;;
        color = thisrgb;
    }
    
    gl_FragColor = vec4(color, 1. );
}