Add example to demonstrate manual generation and UV mapping of 3D mesh (generate_custom_mesh) solve #4922

Cargo.toml

@@ -447,6 +447,16 @@ description = "A scene showcasing the built-in 3D shapes"
 category = "3D Rendering"
 wasm = true
 
+[[example]]
+name = "3d_custom_image"
+path = "examples/3d/3d_custom_image.rs"
+
+[package.metadata.example.3d_custom_image]
+name = "3D custom image"
+description = "Simple showcase of how to use a custom image as a texture for a 3D mesh"
+category = "3D Rendering"
+wasm = true
+
 [[example]]
 name = "anti_aliasing"
 path = "examples/3d/anti_aliasing.rs"

examples/3d/3d_custom_image.rs

@@ -0,0 +1,186 @@
+use bevy::prelude::*;
+use bevy::render::mesh::Indices;
+use bevy::render::render_resource::PrimitiveTopology;
+
+// Notice "ImagePlugin::default_nearest()" in main, because our texture is very low res
+// we want it to look pixelated, instead of the default ImagePlugin::default_linear() which will
+// smooth our pixelated texture. However, default_linear is usually better for high res textures.
+fn main() {
+    App::new()
+        .add_plugins(DefaultPlugins.set(ImagePlugin::default_nearest()))
+        .add_systems(Startup, setup)
+        .add_systems(Update, rotate)
+        .run();
+}
+
+// Rotate the cube to show off all the sides.
+fn rotate(mut query: Query<&mut Transform, With<Handle<Mesh>>>, time: Res<Time>) {
+    for mut transform in &mut query {
+        transform.rotate_z(time.delta_seconds() / 1.2);
+        transform.rotate_x(time.delta_seconds() / 2.0);
+    }
+}
+
+fn setup(
+    mut commands: Commands,
+    asset_server: ResMut<AssetServer>,
+    mut materials: ResMut<Assets<StandardMaterial>>,
+    mut meshes: ResMut<Assets<Mesh>>,
+) {
+    // Importing the custom texture.
+    let custom_texture_handle: Handle<Image> =
+        asset_server.load("textures/custom_image_for_example.png");
+    // Creating and saving a handle to the mesh.
+    let cube_mesh_handle: Handle<Mesh> = meshes.add(create_cube_mesh());
+
+    // Rendering the mesh with the custom texture using a PbrBundle.
+    commands.spawn(PbrBundle {
+        mesh: cube_mesh_handle,
+        material: materials.add(StandardMaterial {
+            base_color_texture: Some(custom_texture_handle),
+            ..default()
+        }),
+        ..default()
+    });
+
+    // Transform for the camera and lighting, looking at (0,0,0) (the position of the mesh).
+    let camera_and_light_transform =
+        Transform::from_xyz(3.0, 3.0, 3.0).looking_at(Vec3::ZERO, Vec3::Y);
+
+    // Camera in 3D space.
+    commands.spawn(Camera3dBundle {
+        transform: camera_and_light_transform,
+        ..default()
+    });
+
+    // Lighting up the scene.
+    commands.spawn(PointLightBundle {
+        point_light: PointLight {
+            intensity: 9000.0,
+            range: 100.0,
+            ..default()
+        },
+        transform: camera_and_light_transform,
+        ..default()
+    });
+}
+
+fn create_cube_mesh() -> Mesh {
+    let mut cube_mesh = Mesh::new(PrimitiveTopology::TriangleList);
+
+    #[rustfmt::skip]
+    cube_mesh.insert_attribute(
+        Mesh::ATTRIBUTE_POSITION,
+        vec![
+            // top (facing towards +y)
+            [0.0, 1.0, 0.0], // vertex with index 0
+            [1.0, 1.0, 0.0], // vertex wtih index 1
+            [1.0, 1.0, 1.0], // etc. until 23
+            [0.0, 1.0, 1.0],
+            // bottom  `  `  (-y)
+            [0.0, 0.0, 0.0],
+            [1.0, 0.0, 0.0],
+            [1.0, 0.0, 1.0],
+            [0.0, 0.0, 1.0],
+            // forward `  `  (+x)
+            [1.0, 0.0, 0.0],
+            [1.0, 0.0, 1.0],
+            [1.0, 1.0, 1.0],
+            [1.0, 1.0, 0.0],
+            // back    `  `  (-x)
+            [0.0, 0.0, 0.0],
+            [0.0, 0.0, 1.0],
+            [0.0, 1.0, 1.0],
+            [0.0, 1.0, 0.0],
+            // right   `  `  (+z)
+            [0.0, 0.0, 1.0],
+            [0.0, 1.0, 1.0],
+            [1.0, 1.0, 1.0],
+            [1.0, 0.0, 1.0],
+            // left    `  `  (-z)
+            [0.0, 0.0, 0.0],
+            [0.0, 1.0, 0.0],
+            [1.0, 1.0, 0.0],
+            [1.0, 0.0, 0.0],
+        ],
+    );
+
+    // Take a look at the custom image (assets/textures/custom_image_for_example.png)
+    // so the UV coords will make more sense (note (0.0, 0.0) = Top-Left in UV mapping).
+    #[rustfmt::skip]
+    cube_mesh.insert_attribute(
+        Mesh::ATTRIBUTE_UV_0,
+        vec![
+            // Assigning the UV coords for the top side.
+            [0.5, 0.0], [0.0, 0.0], [0.0, 0.5], [0.5, 0.5],
+            // Assigning the UV coords for the bottom side.
+            [0.5, 0.5], [0.5, 0.0], [1.0, 0.0], [1.0, 0.5],
+            // Assigning the UV coords for the forward side.
+            [0.5, 1.0], [0.5, 0.5], [1.0, 0.5], [1.0, 1.0],
+            // Assigning the UV coords for the back side (same as forward because they have the
+            // same texture)
+            [0.5, 1.0], [0.5, 0.5], [1.0, 0.5], [1.0, 1.0],
+            // Assigning the UV coords for the right side.
+            [0.0, 1.0], [0.0, 0.5], [0.5, 0.5], [0.5, 1.0],
+            // Assigning the UV coords for the left side (same as right).
+            [0.0, 1.0], [0.0, 0.5], [0.5, 0.5], [0.5, 1.0],
+        ],
+    );
+
+    // When it comes to smooth, and simple meshes, normals are as simple as the direction of the flat surface
+    // Assign normals to allow for correct lighting calculations.
+    #[rustfmt::skip]
+    cube_mesh.insert_attribute(
+        Mesh::ATTRIBUTE_NORMAL,
+        vec![
+            // Normals for the top side (towards +y)
+            [0.0, 1.0, 0.0],
+            [0.0, 1.0, 0.0],
+            [0.0, 1.0, 0.0],
+            [0.0, 1.0, 0.0],
+            // Normals for the bottom side (towards -y)
+            [0.0, -1.0, 0.0],
+            [0.0, -1.0, 0.0],
+            [0.0, -1.0, 0.0],
+            [0.0, -1.0, 0.0],
+            // Normals for the forward side (towards +x)
+            [1.0, 0.0, 0.0],
+            [1.0, 0.0, 0.0],
+            [1.0, 0.0, 0.0],
+            [1.0, 0.0, 0.0],
+            // Normals for the back side (towards -x)
+            [-1.0, 0.0, 0.0],
+            [-1.0, 0.0, 0.0],
+            [-1.0, 0.0, 0.0],
+            [-1.0, 0.0, 0.0],
+            // Normals for the right side (towards +z)
+            [0.0, 0.0, 1.0],
+            [0.0, 0.0, 1.0],
+            [0.0, 0.0, 1.0],
+            [0.0, 0.0, 1.0],
+            // Normals for the left side (towards -z)
+            [0.0, 0.0, -1.0],
+            [0.0, 0.0, -1.0],
+            [0.0, 0.0, -1.0],
+            [0.0, 0.0, -1.0],
+        ],
+    );
+
+    // Create the triangles out of the 24 vertices we created.
+    // To construct a square, we need 2 triangles, therfore 12 traingles in total.
+    // To construct a triangle, we need the indices of 3 of its defined vertices, adding them one
+    // by one, in a counter-clockwise order (relative to the position of the viewer, the order
+    // should appear counter-clockwise from the front of the triangle). Read more about how to correctly build a mesh manually
+    // in the Bevy documentation, further examples and the implementation of the built-in shapes.
+    #[rustfmt::skip]
+    cube_mesh.set_indices(Some(Indices::U32(vec![
+        0,3,1 , 1,3,2, // top (+y)
+        4,5,7 , 5,6,7, // bottom (-y)
+        8,11,9 , 9,11,10, // forward (+x)
+        12,13,15 , 13,14,15, // backward (-x)
+        16,19,17 , 17,19,18, // rightward (+z)
+        20,21,23 , 21,22,23, // leftward (-z)
+    ])));
+
+    cube_mesh
+}

examples/README.md

@@ -116,6 +116,7 @@ Example | Description
 [3D Gizmos](../examples/3d/3d_gizmos.rs) | A scene showcasing 3D gizmos
 [3D Scene](../examples/3d/3d_scene.rs) | Simple 3D scene with basic shapes and lighting
 [3D Shapes](../examples/3d/3d_shapes.rs) | A scene showcasing the built-in 3D shapes
+[3D custom image](../examples/3d/3d_custom_image.rs) | Simple showcase of how to use a custom image as a texture for a 3D mesh
 [Anti-aliasing](../examples/3d/anti_aliasing.rs) | Compares different anti-aliasing methods
 [Atmospheric Fog](../examples/3d/atmospheric_fog.rs) | A scene showcasing the atmospheric fog effect
 [Blend Modes](../examples/3d/blend_modes.rs) | Showcases different blend modes