Tweak demos (#146)

openrndr-demos/src/demo/kotlin/DemoCircleBatch02.kt

@@ -1,27 +1,42 @@
 import org.openrndr.application
 import org.openrndr.color.ColorRGBa
 import org.openrndr.draw.circleBatch
+import org.openrndr.draw.shadeStyle
 
 /*
-This program demonstrates creating "pre-baked" batches of circles. Batches can have varying fill, stroke and
-strokeWeight settings.
+This program demonstrates creating "pre-baked" batches of circles.
+Batches can have varying fill, stroke and strokeWeight settings.
 
-Batches are (currently) static but stored in GPU memory. Batches are fast to draw.
- */
+Batches are (currently) static but stored in GPU memory but can be
+animated using a vertex shader. Batches are fast to draw.
+*/
 
 fun main() = application {
     program {
-
         val batch = drawer.circleBatch {
-            this.fill = ColorRGBa.PINK
-            for (i in 0 until 100) {
-                this.strokeWeight = Math.random() * 5.0
-                this.circle(Math.random() * width, Math.random() * height, 50.0 * Math.random()  + 50.0 )
+            for (i in 0 until 2000) {
+                fill = ColorRGBa.PINK.shade(Math.random())
+                strokeWeight = Math.random() * 5
+                circle(width * 0.5, height * 0.5, 20 * Math.random() + 5)
             }
         }
 
         extend {
             drawer.clear(ColorRGBa.GRAY)
+
+            // The following optional shadeStyle animates the batch
+            // by using polar coordinates:
+            // sets angle and radius based on time and shape ID.
+            drawer.shadeStyle = shadeStyle {
+                vertexTransform = """
+                    float a = c_instance + p_time * 0.1;
+                    float r = 200 + 100 * sin(a * 0.998);
+                    x_position.x += r * sin(a);
+                    x_position.y += r * cos(a);
+                """.trimIndent()
+                parameter("time", seconds)
+            }
+
             drawer.circles(batch)
         }
     }