fragment uv flip glsl shader and wondering how i can replace the if statements with working math

Question

//This has been tested and works in AGK classic
#ifdef GL_ES
    precision mediump float;
    precision mediump int;
#endif
#define PROCESSING_TEXTURE_SHADER
varying mediump vec2 uvVarying;
uniform sampler2D texture0;
uniform vec2 rot;  //where rot is a vector passed to the shader from my AGK program
void main(void)
{
    vec2 p = uvVarying;
    if (rot.x ==1.0)
        {p.x=rot.x-p.x;}  
    if (rot.y==1.0)")
        {p.y=rot.y-p.y;}
    vec3 col = texture2D(texture0, p).rgb;
    gl_FragColor = vec4(col, 1.0);
}

without the if statements i.e and rot.x =0 then "p.x=rot.x-p.x" fails (the same for the second vector rot.y im looking for a simple math work around that removes the if statement for performance

Answer 1

if you want to remove if statement and your rot.x and rot.y values could be either 0.0 or 1.0, then I would suggest to try with a mix function

vec2 p = mix(uvVarying, rot - uvVarying, rot);