[WIP] start 1.15 port

reorganize packages to match Fabric version
use util classes from Fabric version

src/main/kotlin/mods/betterfoliage/resource/generated/GeneratedGrass.kt

@@ -0,0 +1,56 @@
+package mods.betterfoliage.resource.generated
+
+import mods.betterfoliage.resource.Identifier
+import mods.betterfoliage.texture.blendRGB
+import mods.betterfoliage.texture.loadSprite
+import mods.betterfoliage.util.Atlas
+import mods.betterfoliage.util.bytes
+import mods.betterfoliage.util.get
+import mods.betterfoliage.util.set
+import mods.octarinecore.client.resource.*
+import net.minecraft.resources.IResourceManager
+import java.awt.image.BufferedImage
+
+/**
+ * Generate Short Grass textures from [Blocks.tallgrass] block textures.
+ * The bottom 3/8 of the base texture is chopped off.
+ *
+ * @param[domain] Resource domain of generator
+ */
+data class GeneratedGrass(val sprite: Identifier, val isSnowed: Boolean, val atlas: Atlas = Atlas.BLOCKS) {
+    constructor(sprite: String, isSnowed: Boolean) : this(Identifier(sprite), isSnowed)
+
+    fun register(pack: GeneratedBlockTexturePack) = pack.register(this, this::draw)
+
+    fun draw(resourceManager: IResourceManager): ByteArray {
+        val baseTexture = resourceManager.loadSprite(atlas.wrap(sprite))
+
+        val result = BufferedImage(baseTexture.width, baseTexture.height, BufferedImage.TYPE_4BYTE_ABGR)
+        val graphics = result.createGraphics()
+
+        val size = baseTexture.width
+        val frames = baseTexture.height / size
+
+        // iterate all frames
+        for (frame in 0 until frames) {
+            val baseFrame = baseTexture.getSubimage(0, size * frame, size, size)
+            val grassFrame = BufferedImage(size, size, BufferedImage.TYPE_4BYTE_ABGR)
+
+            // draw bottom half of texture
+            grassFrame.createGraphics().apply {
+                drawImage(baseFrame, 0, 3 * size / 8, null)
+            }
+
+            // add to animated png
+            graphics.drawImage(grassFrame, 0, size * frame, null)
+        }
+
+        // blend with white if snowed
+        if (isSnowed) {
+            for (x in 0..result.width - 1) for (y in 0..result.height - 1) {
+                result[x, y] = blendRGB(result[x, y], 16777215, 2, 3)
+            }
+        }
+        return result.bytes
+    }
+}