Add StretchWaves filter

orx-fx/src/main/kotlin/distort/StretchWaves.kt

@@ -0,0 +1,41 @@
+package org.openrndr.extra.fx.distort
+
+import org.openrndr.draw.*
+import org.openrndr.extra.fx.filterFragmentCode
+import org.openrndr.extra.parameters.Description
+import org.openrndr.extra.parameters.DoubleParameter
+
+@Description("Stretch waves")
+class StretchWaves : Filter(filterShaderFromCode(filterFragmentCode("distort/stretch-waves.frag"))) {
+    @DoubleParameter("distortion", -0.0,1.0, 1)
+    var distortion: Double by parameters
+
+    @DoubleParameter("rotation", -180.0, 180.0)
+    var rotation: Double by parameters
+
+    @DoubleParameter("phase", -1.0, 1.0)
+    var phase: Double by parameters
+
+    @DoubleParameter("frequency", 0.0, 100.0)
+    var frequency: Double by parameters
+
+    @DoubleParameter("feather", 0.0, 100.0, order = 1)
+    var feather: Double by parameters
+
+    init {
+        distortion = 0.0
+        rotation = 0.0
+        phase = 0.0
+        frequency = 10.0
+        feather = 1.0
+    }
+
+    var bicubicFiltering = true
+    override fun apply(source: Array<ColorBuffer>, target: Array<ColorBuffer>) {
+        if (bicubicFiltering && source.isNotEmpty()) {
+            source[0].generateMipmaps()
+            source[0].filter(MinifyingFilter.LINEAR_MIPMAP_LINEAR, MagnifyingFilter.LINEAR)
+        }
+        super.apply(source, target)
+    }
+}

orx-fx/src/main/resources/org/openrndr/extra/fx/gl3/distort/stretch-waves.frag

@@ -0,0 +1,42 @@
+#version 330 core
+
+uniform sampler2D tex0;
+in vec2 v_texCoord0;
+
+uniform float phase;
+uniform float rotation;
+uniform float distortion;
+uniform float frequency;
+uniform float feather;
+out vec4 o_color;
+
+void main() {
+    float phi = radians(rotation);
+    float cp = cos(phi);
+    float sp = sin(phi);
+    mat2 rm = mat2(vec2(cp, sp), vec2(-sp, cp));
+    mat2 irm = transpose(rm);
+
+    float tw = 1.0 / frequency;
+    vec2 uv = rm * (v_texCoord0 - vec2(0.5)) + vec2(0.5) + vec2(phase * tw, 0.0);
+
+    float xd = (uv.x) * frequency;
+    float xo = (fract(xd) - 0.5) * 2.0;
+    float xf = fract(xd);
+
+    float offs = (1.0- xo * xo) * 1.0 * xo * distortion * 0.5;
+    float f = mix(1.0, (1.0 - xo * xo), distortion);
+
+    vec2 fuv = uv;
+    fuv.x = floor(uv.x * frequency) / frequency;
+    fuv.x += (xf - offs) * tw;
+
+    fuv = irm * (fuv - vec2(0.5) - vec2(phase * tw, 0.0)) + vec2(0.5);
+
+    vec2 step = fwidth(fuv) * feather;
+    float fx = smoothstep(0.0, step.x, fuv.x) * smoothstep(1.0, 1.0 - step.x, fuv.x);
+    float fy = smoothstep(0.0, step.y, fuv.y) * smoothstep(1.0, 1.0 - step.y, fuv.y);
+
+    vec4 c = texture(tex0, fuv) * f * fx * fy;
+    o_color = c;
+}