Added Sprite Local UV example

Author: britzl

material/sprite_local_uv/all.texture_profiles

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+path_settings {
+  path: "**"
+  profile: "Default"
+}
+profiles {
+  name: "Default"
+  platforms {
+    os: OS_ID_GENERIC
+    formats {
+      format: TEXTURE_FORMAT_RGBA
+      compression_level: BEST
+      compression_type: COMPRESSION_TYPE_DEFAULT
+    }
+    mipmaps: false
+    max_texture_size: 0
+    premultiply_alpha: true
+  }
+}

material/sprite_local_uv/assets/images/elementStone019.png

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+images {
+  image: "/assets/images/elementStone019.png"
+}
+images {
+  image: "/assets/images/elementStone023.png"
+}
+extrude_borders: 2

material/sprite_local_uv/assets/images/elementStone023.png

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+---
+tags: sprite
+title: Sprite local UV
+brief: This example shows how to get local UV coordinates of a sprite regardless of sprite size
+author: Defold Foundation
+scripts: sprite_local_uv.script, sprite_local_uv.vp, sprite_local_uv.fp
+---
+
+The example uses two game objects, each with a sprite component and a script.
+
+![example](example.png)
+
+The sprite component uses a custom sprite material `sprite_local_uv.material` with `local_position` and `sprite_size` as two vertex attributes. The `local_position` attribute is of semantic type "Position" and coordinate space "Local" while the `sprite_size` attribute is of semantic type "User" and will be set by the script.
+
+![material](material.png)
+
+The script gets the size of the sprite and sets it as the `sprite_size` vertex attribute.

material/sprite_local_uv/assets/sprites.atlas

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+name: "sprite_local_uv"
+scale_along_z: 0
+embedded_instances {
+  id: "square"
+  data: "components {\n"
+  "  id: \"size\"\n"
+  "  component: \"/example/sprite_local_uv.script\"\n"
+  "}\n"
+  "embedded_components {\n"
+  "  id: \"sprite\"\n"
+  "  type: \"sprite\"\n"
+  "  data: \"default_animation: \\\"elementStone023\\\"\\n"
+  "material: \\\"/example/sprite_local_uv.material\\\"\\n"
+  "textures {\\n"
+  "  sampler: \\\"texture_sampler\\\"\\n"
+  "  texture: \\\"/assets/sprites.atlas\\\"\\n"
+  "}\\n"
+  "\"\n"
+  "}\n"
+  ""
+  position {
+    x: 360.0
+    y: 200.0
+  }
+}
+embedded_instances {
+  id: "rectangle"
+  data: "components {\n"
+  "  id: \"size\"\n"
+  "  component: \"/example/sprite_local_uv.script\"\n"
+  "}\n"
+  "embedded_components {\n"
+  "  id: \"sprite\"\n"
+  "  type: \"sprite\"\n"
+  "  data: \"default_animation: \\\"elementStone019\\\"\\n"
+  "material: \\\"/example/sprite_local_uv.material\\\"\\n"
+  "size {\\n"
+  "  x: 140.0\\n"
+  "  y: 140.0\\n"
+  "}\\n"
+  "textures {\\n"
+  "  sampler: \\\"texture_sampler\\\"\\n"
+  "  texture: \\\"/assets/sprites.atlas\\\"\\n"
+  "}\\n"
+  "\"\n"
+  "}\n"
+  ""
+  position {
+    x: 360.0
+    y: 500.0
+  }
+}

material/sprite_local_uv/example.md

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+#version 140
+
+// from sprite_local_uv.vp
+in mediump vec2 var_texcoord0;
+in highp vec2 var_position_local;
+
+out vec4 out_fragColor;
+
+uniform mediump sampler2D texture_sampler;
+uniform fs_uniforms
+{
+    mediump vec4 tint;
+};
+
+void main()
+{
+    // Pre-multiply alpha since all runtime textures already are
+    mediump vec4 tint_pm = vec4(tint.xyz * tint.w, tint.w);
+
+    // sample color from sprite texture
+    vec4 color = texture(texture_sampler, var_texcoord0.xy) * tint_pm;
+
+    // mix local position with red and green color of sprite to
+    // create a gradient across the entire sprite
+    out_fragColor.rg = mix(color.rg, var_position_local.xy, 0.3);
+    // use blue and alpha from the sprite
+    out_fragColor.b = color.b;
+    out_fragColor.a = color.a;
+}

material/sprite_local_uv/example.png

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+name: "sprite"
+tags: "tile"
+vertex_program: "/example/sprite_local_uv.vp"
+fragment_program: "/example/sprite_local_uv.fp"
+vertex_constants {
+  name: "view_proj"
+  type: CONSTANT_TYPE_VIEWPROJ
+}
+fragment_constants {
+  name: "tint"
+  type: CONSTANT_TYPE_USER
+  value {
+    x: 1.0
+    y: 1.0
+    z: 1.0
+    w: 1.0
+  }
+}
+samplers {
+  name: "texture_sampler"
+  wrap_u: WRAP_MODE_CLAMP_TO_EDGE
+  wrap_v: WRAP_MODE_CLAMP_TO_EDGE
+  filter_min: FILTER_MODE_MIN_DEFAULT
+  filter_mag: FILTER_MODE_MAG_DEFAULT
+}
+attributes {
+  name: "position_local"
+  semantic_type: SEMANTIC_TYPE_POSITION
+  vector_type: VECTOR_TYPE_VEC2
+}
+attributes {
+  name: "sprite_size"
+  double_values {
+    v: 64.0
+    v: 64.0
+  }
+  vector_type: VECTOR_TYPE_VEC2
+}

material/sprite_local_uv/example/sprite_local_uv.collection

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+function init(self)
+	-- get the sprite size from the sprite component propertry 'size'
+	local size = go.get("#sprite", "size")
+
+	-- set the size on the sprite material in the custom vertex attribute 'sprite_size'
+	go.set("#sprite", "sprite_size", size)
+
+	-- rotate the sprite
+	go.animate(".", "euler.z", go.PLAYBACK_LOOP_FORWARD, 360, go.EASING_LINEAR, 5)
+end