mesh: Fix voxel mesh generation ignoring prefer_textures.

Part of fixing <#504>.
This is the last of the bugs affecting the `emission_only` render test!

all-is-cubes-mesh/src/block_mesh/compute.rs

@@ -134,7 +134,7 @@ pub(super) fn compute_block_mesh<M: MeshTypes>(
         }
         let output_interior = &mut output.interior_vertices;
 
-        let texture_if_needed: Option<M::Tile> = if analysis.needs_texture {
+        let texture_if_needed: Option<M::Tile> = if prefer_textures || analysis.needs_texture {
             texture::copy_voxels_to_new_texture(texture_allocator, voxels)
         } else {
             None

all-is-cubes-mesh/src/tests.rs

@@ -190,6 +190,36 @@ fn animated_atom_uses_texture() {
     )
 }
 
+/// For relevantly animated blocks we always prefer textures, even if the voxels are currently all
+/// identical.
+#[test]
+fn animated_voxels_uses_texture() {
+    let mut u = Universe::new();
+    let block = Block::builder()
+        .voxels_fn(R2, |_| const { &color_block!(Rgba::WHITE) })
+        .unwrap()
+        .animation_hint(block::AnimationHint::redefinition(
+            block::AnimationChange::ColorSameCategory,
+        ))
+        .build_into(&mut u);
+
+    let (allocator, _, mesh) = mesh_blocks_and_space(
+        &Space::builder(GridAab::ORIGIN_CUBE)
+            .filled_with(block)
+            .build(),
+    );
+
+    assert_eq!(allocator.count_allocated(), 1);
+    assert_eq!(
+        mesh.vertices()[0].coloring,
+        Coloring::Texture {
+            pos: point3(0.5, 0., 0.),
+            clamp_min: point3(0.5, 0.5, 0.5),
+            clamp_max: point3(0.5, 1.5, 1.5)
+        }
+    )
+}
+
 /// We don't encode light emission in vertex colors (because that would lead to bloated vertices),
 /// so a block with light emission will use a texture, even for resolution 1.
 ///
@@ -219,7 +249,7 @@ fn emissive_atom_uses_texture() {
 }
 
 /// Test handling of the case where `color` is transparent and `light_emission` is nonzero;
-/// it should have a nonempty mesh.
+/// for an atom (resolution-1) block; it should have a nonempty mesh.
 #[test]
 fn emissive_only_atom() {
     let atom_block = Block::builder()
@@ -246,6 +276,36 @@ fn emissive_only_atom() {
     )
 }
 
+/// Test handling of the case where `color` is transparent and `light_emission` is nonzero,
+/// for a non-atom (non-resolution-1) block; it should have a nonempty mesh.
+#[test]
+fn emissive_only_voxels() {
+    let mut u = Universe::new();
+    let atom_block = Block::builder()
+        .color(Rgba::TRANSPARENT)
+        .light_emission(Rgb::ONE)
+        .build();
+    let voxel_block = Block::builder()
+        .voxels_fn(R2, |cube| {
+            if cube == Cube::ORIGIN {
+                &atom_block
+            } else {
+                &AIR
+            }
+        })
+        .unwrap()
+        .build_into(&mut u);
+    let (allocator, block_meshes, space_mesh) = mesh_blocks_and_space(
+        &Space::builder(GridAab::ORIGIN_CUBE)
+            .filled_with(voxel_block)
+            .build(),
+    );
+
+    assert!(!block_meshes[0].is_empty());
+    assert!(!space_mesh.is_empty());
+    assert_eq!(allocator.count_allocated(), 1);
+}
+
 /// [`SpaceMesh`] of a 1×1×1 space has the same geometry as the contents.
 ///
 /// This test compares 3 different values:

test-renderers/src/test_cases.rs

@@ -332,16 +332,9 @@ async fn emission_only(mut context: RenderTestContext, transparency_option: &str
     };
     let cameras = StandardCameras::from_constant_for_test(options, COMMON_VIEWPORT, &universe);
 
-    // TODO: This test doesn't currently work yet. In order to be able to run it and
-    // investigate its output, we mark the image as flawed so that comparison failures
-    // don't count.
-    {
-        let mut renderer = context.renderer(cameras);
-        renderer.update(None).await.unwrap();
-        let mut image = renderer.draw("").await.unwrap();
-        image.flaws.insert(Flaws::OTHER);
-        context.compare_image(1, image);
-    }
+    context
+        .render_comparison_test(1, cameras, Overlays::NONE)
+        .await;
 }
 
 /// Test what happens when the renderer's character goes away *after* the first frame.