more depth to the distant clouds

src/net/torvald/terrarum/weather/WeatherObjectCloud.kt

@@ -5,12 +5,13 @@ import com.badlogic.gdx.graphics.g2d.TextureRegion
 import com.badlogic.gdx.math.Vector2
 import com.badlogic.gdx.math.Vector3
 import net.torvald.terrarum.App
+import kotlin.math.pow
 import kotlin.math.sign
 
 /**
  * Created by minjaesong on 2023-08-21.
  */
-class WeatherObjectCloud(private val texture: TextureRegion, private val flipW: Boolean) : WeatherObject() {
+class WeatherObjectCloud(private val texture: TextureRegion, private val flipW: Boolean) : WeatherObject(), Comparable<WeatherObjectCloud> {
 
     /**
      * To actually utilise this value, your render code must begin the spritebatch per-object, like so:
@@ -26,6 +27,7 @@ class WeatherObjectCloud(private val texture: TextureRegion, private val flipW:
     var darkness: Vector2 = Vector2(0.5f, 2.0f) // the "gamma" value fed into the clouds shader
 
     override fun update() {
+        throw UnsupportedOperationException()
     }
 
     /**
@@ -33,30 +35,71 @@ class WeatherObjectCloud(private val texture: TextureRegion, private val flipW:
      * Resulting vector: (x + dX, y + dY, scale * dScale)
      */
     fun update(flowVector: Vector3, gait: Float) {
-        val vecMult = Vector3(1f, 1f, 1f / (2f * App.scr.hf * 0.35f))
         pos.add(flowVector.cpy().scl(vecMult).scl(gait))
+
+        alpha = -(posZ / ALPHA_ROLLOFF_Z).pow(1.703f) + 1f
+
+        val lrCoord = screenCoordBottomLR
+        if (lrCoord.x > WeatherMixer.oobMarginR || lrCoord.z < WeatherMixer.oobMarginL || posZ !in 0.05f..ALPHA_ROLLOFF_Z || alpha < 1f / 255f) {
+            flagToDespawn = true
+        }
     }
 
+    private val w = App.scr.halfwf
+    private val h = App.scr.hf * 0.5f
+    private val vecMult = Vector3(1f, 1f, 1f / (2f * h))
+
     /**
      * X/Y position is a bottom-centre point of the image
      * Shader must be prepared prior to the render() call
      */
     override fun render(batch: SpriteBatch, offsetX: Float, offsetY: Float) {
-        val x = posX + offsetX - texture.regionWidth * scale * 0.5f
-        val y = posY + offsetY - texture.regionHeight * scale
-        val z = posZ // must be at least 1.0
-        val w = App.scr.halfwf
-        val h = App.scr.hf * 0.35f
-
-        val drawX = (x + w * (z-1)) / z
-        val drawY = (y + h * (z-1)) / z
-        val drawScale = scale / z
+        val sc = screenCoord
 
         if (flipW)
-            batch.draw(texture, drawX + texture.regionWidth / z, drawY, -texture.regionWidth * drawScale, texture.regionHeight * drawScale)
+            batch.draw(texture, sc.x + texture.regionWidth / posZ, sc.y, -texture.regionWidth * sc.z, texture.regionHeight * sc.z)
         else
-            batch.draw(texture, drawX, drawY, texture.regionWidth * drawScale, texture.regionHeight * drawScale)
+            batch.draw(texture, sc.x, sc.y, texture.regionWidth * sc.z, texture.regionHeight * sc.z)
     }
 
+    /**
+     * vec3(screen X, screenY, draw scale)
+     */
+    val screenCoord: Vector3
+        get() {
+            val x = posX - texture.regionWidth * scale * 0.5f
+            val y = posY - texture.regionHeight * scale
+            val z = posZ // must be at least 1.0
+
+            val drawX = (x + w * (z-1)) / z
+            val drawY = (y + h * (z-1)) / z
+            val drawScale = scale / z
+
+            return Vector3(drawX, drawY, drawScale)
+        }
+
+    /**
+     * vec3(screen-X of bottom-left point, screen-Y, screen-X of bottom-right point)
+     */
+    val screenCoordBottomLR: Vector3
+        get() {
+            val xL = posX - texture.regionWidth * scale * 0.5f
+            val xR = posX + texture.regionWidth * scale * 0.5f
+            val y = posY - texture.regionHeight * scale
+            val z = posZ // must be at least 1.0
+
+            val drawXL = (xL + w * (z-1)) / z
+            val drawXR = (xR + w * (z-1)) / z
+            val drawY = (y + h * (z-1)) / z
+
+            return Vector3(drawXL, drawY, drawXR)
+        }
+
     override fun dispose() { /* cloud texture will be disposed of by the WeatherMixer */ }
+    override fun compareTo(other: WeatherObjectCloud): Int = (other.posZ - this.posZ).sign.toInt()
+
+    companion object {
+        fun screenXtoWorldX(screenX: Float, z: Float) = screenX * z - App.scr.halfwf * (z - 1f)
+        const val ALPHA_ROLLOFF_Z = 16f
+    }
 }