[orx-jumpflood] Make module multiplatform

orx-jumpflood/src/shaders/glsl/sdf-smooth-union.frag

@@ -0,0 +1,17 @@
+uniform sampler2D tex0; // signed distance
+uniform sampler2D tex1; // signed distance
+uniform float radius;
+
+in vec2 v_texCoord0;
+out vec4 o_color;
+
+float opSmoothUnion(float d1, float d2, float k) {
+    float h = clamp(0.5 + 0.5*(d2-d1)/k, 0.0, 1.0);
+    return mix(d2, d1, h) - k*h*(1.0-h);
+}
+
+void main() {
+    float d0 = texture(tex0, v_texCoord0).r;
+    float d1 = texture(tex1, v_texCoord0).r;
+    o_color = vec4(opSmoothUnion(d0, d1, radius), 0.0, 0.0, 1.0);
+}