[orx-fx] Add comments to demos

orx-fx/src/jvmDemo/kotlin/DemoSpectralBlend01.kt

@@ -8,6 +8,20 @@ import org.openrndr.extra.fx.patterns.Checkers
 import org.openrndr.math.Vector2
 import kotlin.math.sin
 
+/**
+ * Demonstration of how to use the [BlendSpectral] filter to combine two images, using
+ * this pigment-simulation color mixing approach.
+ *
+ * The program:
+ * - generates two images
+ * - blurs one of them
+ * - creates and draws a checkers-pattern as the background
+ * - mixes and draws both images
+ *
+ * The `fill` factor, which controls how the top and the bottom colors are mixed, is animated.
+ *
+ * The `clip` parameter is also animated and toggles every 6 seconds.
+ */
 fun main() = application {
     configure {
         width = 800
@@ -35,7 +49,7 @@ fun main() = application {
         extend {
             drawer.image(checked)
             blendSpectral.fill = sin(seconds) * 0.5 + 0.5
-            blendSpectral.clip = seconds.mod(4.0) > 2.0
+            blendSpectral.clip = seconds.mod(12.0) > 6.0
             blendSpectral.apply(a, b, mixed)
             drawer.image(mixed)
         }