openRNDR demo for doing an inversion distortion effect

distortion.kt

import org.openrndr.application
import org.openrndr.draw.isolatedWithTarget
import org.openrndr.draw.renderTarget
import org.openrndr.draw.shadeStyle
import org.openrndr.extra.compositor.compose
import org.openrndr.extra.compositor.draw
import org.openrndr.ffmpeg.ScreenRecorder

// shader-based inversion distortion effect
// this demonstrates inversion (1/z) (https://mathworld.wolfram.com/ConformalMapping.html)
fun main() = application {

    configure {
        width = 920
        height = 920
    }

    program {

        val backgroundImage = renderTarget(width, height) { colorBuffer() }

        extend {

            // render checkerboard for example:
            drawer.isolatedWithTarget(backgroundImage) {
                shadeStyle = shadeStyle {
                    fragmentTransform = """  
                        vec2 pos = c_boundsPosition.xy;
                        pos *= 10;
                        float value = mod(int(pos.x) + int(pos.y), 2);
                        x_fill.rgb = vec3(value);
                    """
                }
                rectangle(bounds)
            }

            // this does the actual distortion effect
            drawer.shadeStyle = shadeStyle {
                fragmentTransform = """
                    vec2 pos = c_boundsPosition.xy;       // current pixel
                    vec2 origin = vec2(0.5, 0.5);         // the center, which could vary with time
                                                          
                    float dist = distance(pos, origin);
                    
                    // play around with clamping the distance for different effect in the center
                    dist += 0.1;                           
                                                          
                    // get the "direction vector" to the pixel:
                    vec2 dir = normalize(pos - origin);   

                    // the position along the "boundary circle":
                    vec2 circlePosition = 0.1 * dir;
                    
                    // perform inversion with respect to the circle:
                    vec2 newPos = circlePosition / dist;    

                    // convert back to shader screen coordinates:
                    newPos += origin;                     

                    // mod the values back into the 0-1 range if necessary:
                    newPos = fract(newPos);                

                    // set the final pixel color:
                    x_fill = texture(p_image, newPos);    
                    
                """.trimIndent()
                parameter("image", backgroundImage.colorBuffer(0))
            }

            // draw the final output
            drawer.image(backgroundImage.colorBuffer(0))
        }
    }
}