Texture tweens

content/ADR-255-texture-tweens.md

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+---
+layout: adr
+adr: 255
+title: Texture tweens
+date: 2024-12-02
+status: Draft
+type: RFC
+spdx-license: CC0-1.0
+authors:
+  - nearnshaw
+---
+
+# Abstract
+
+This document describes an approach for making it possible for creators to animate textures. This can be used to simulate running liquids, as well as many other interesting texture effects.
+
+This new feature combines very well with ADR-254 (GLTF Nodes), as it enables to do the same effects on the textures of any .gltf model.
+
+## Offset and tiling
+
+Today the settings available on a texture are limited. We need to be able to also change the offset and the scale of a texture. As part of this ADR we're also adding two new fields to all textures:
+
+- `offset`: _Vector2_, shifts the image from starting on the 0,0 mark. Default value `0,0`
+- `tiling`: _Vector2_, determines how many times the texture fits on the surface. Default value `1,1`. The behavior of the remaining space on the texture will depend on the value of `wrapMode`.
+
+A creator could theoretically write a system that changes the `offset` value on every frame, but that would be very bad for performance. If something will continually change their offset, it's recommended to instead use a Tween for that.
+
+## Texture tween
+
+We'll define a new type of tween that affects the Material rather than the Transform. This is enabled by using the already existing Tween and TweenSequence components, with a new `TextureMove` option to be added to the existing `Move`, `Rotate`, and `Scale`.
+
+The new `TextureMove` option on the `Tween` component will have the following fields:
+
+- `TextureMovementType`: _(optional)_, defines if the movement will be on the `offset` or the `tiling` field (see section above)
+- `start`: _Vector2_ the initial value of the offset or tiling
+- `end`: _Vector2_ the final value of the offset or tiling
+- `duration`: _number_ how long the transition takes, in milliseconds
+- `easingFunction`: How the curve of movement over time changes, the default value is `EasingFunction.EF_LINEAR`
+
+The scene can also use a `TweenSequence` to make continuos movements possible, just like with other kinds of tweens.
+
+## Texture layers
+
+Materials have several textures besides the albedo_texture, including bump_texture, alpha_texture, emissive_texture. The `TextureMove` Tween affects the base texture, so all textures move together with it.
+
+This applies to changing the `offset` and `tiling` fields manually, as well as using a texture tween.
+
+## Serialization
+
+```yaml
+parameters:
+  COMPONENT_ID: 1102
+  COMPONENT_NAME: core::Tween
+  CRDT_TYPE: LastWriteWin-Element-Set
+```
+
+```protobuf
+message Texture {
+  string src = 1;
+  optional TextureWrapMode wrap_mode = 2; // default = TextureWrapMode.Clamp
+  optional TextureFilterMode filter_mode = 3; // default = FilterMode.Bilinear
+
+  // Final uv = offset + (input_uv * tiling)
+  optional Vector2 offset = 4; // default = Vector2.Zero; Offset for texture positioning, only works for the texture property in PbrMaterial or UnlitMaterial.
+  optional Vector2 tiling = 5; // default = Vector2.One; Tiling multiplier for texture repetition, only works for the texture property in PbrMaterial or UnlitMaterial.
+}
+
+message PBTween {
+  float duration = 1; // in milliseconds
+  EasingFunction easing_function = 2;
+
+  oneof mode {
+    Move move = 3;
+    Rotate rotate = 4;
+    Scale scale = 5;
+    TextureMove texture_move = 8;
+  }
+
+  optional bool playing = 6; // default true (pause or running)
+  optional float current_time = 7; // between 0 and 1
+}
+
+// This tween mode allows to move the texture of a PbrMaterial or UnlitMaterial.
+// You can also specify the movement type (offset or tiling)
+message TextureMove {
+  decentraland.common.Vector2 start = 1;
+  decentraland.common.Vector2 end = 2;
+  optional TextureMovementType movement_type = 3; // default = TextureMovementType.TMT_OFFSET
+}
+
+enum TextureMovementType {
+  TMT_OFFSET = 0; // default = TextureMovementType.TMT_OFFSET
+  TMT_TILING = 1;
+}
+```
+
+## Semantics
+
+### Example
+
+Offset texture:
+
+```ts
+Material.setPbrMaterial(myEntity, {
+	texture: Material.Texture.Common({
+		src: 'assets/materials/wood.png',
+		wrapMode: TextureWrapMode.TWM_REPEAT,
+		offset: Vector2.create(0, 0.2),
+		tiling: Vector2.create(1, 1),
+	}),
+})
+```
+
+Simple continuos flow:
+
+```ts
+const myEntity = engine.addEntity()
+
+MeshRenderer.setPlane(myEntity)
+
+Transform.create(myEntity, {
+	position: Vector3.create(4, 1, 4),
+})
+
+Material.setPbrMaterial(myEntity, {
+	texture: Material.Texture.Common({
+		src: 'materials/water.png',
+		wrapMode: TextureWrapMode.TWM_REPEAT,
+	}),
+})
+
+Tween.create(myEntity, {
+	mode: Tween.Mode.TextureMove({
+		start: Vector2.create(0, 0),
+		end: Vector2.create(0, 1),
+	}),
+	duration: 1000,
+	easingFunction: EasingFunction.EF_LINEAR,
+})
+
+TweenSequence.create(myEntity, { sequence: [], loop: TweenLoop.TL_RESTART })
+```
+
+Square-moving tween sequence:
+
+```ts
+//(...)
+
+Tween.create(myEntity, {
+	mode: Tween.Mode.TextureMove({
+		start: Vector2.create(0, 0),
+		end: Vector2.create(0, 1),
+	}),
+	duration: 1000,
+	easingFunction: EasingFunction.EF_LINEAR,
+})
+
+TweenSequence.create(myEntity, {
+	sequence: [
+		{
+			mode: Tween.Mode.TextureMove({
+				start: Vector2.create(0, 1),
+				end: Vector2.create(1, 1),
+			}),
+			duration: 1000,
+			easingFunction: EasingFunction.EF_LINEAR,
+		},
+		{
+			mode: Tween.Mode.TextureMove({
+				start: Vector2.create(1, 1),
+				end: Vector2.create(1, 0),
+			}),
+			duration: 1000,
+			easingFunction: EasingFunction.EF_LINEAR,
+		},
+		{
+			mode: Tween.Mode.TextureMove({
+				start: Vector2.create(1, 0),
+				end: Vector2.create(0, 0),
+			}),
+			duration: 1000,
+			easingFunction: EasingFunction.EF_LINEAR,
+		},
+	],
+	loop: TweenLoop.TL_RESTART,
+})
+```