Fix transforming surface normals (#3722)

* Fix transforming surface normals

Fixes #3702

* Fix missing rotation in `normalmatrix`

See #3722 (comment)

* Add reference test "Ellipsoid marker sizes" in ReferenceTests/src/tests/examples3d.jl

* Add a record in CHANGELOG.md

* change 1:3 to Vec(1,2,3)

* tweak changelog entry

---------

Co-authored-by: ffreyer <frederic481994@hotmail.de>

CHANGELOG.md

@@ -8,6 +8,7 @@
 - Fixed `contourf` bug where n levels would sometimes miss the uppermost value, causing gaps [#3713](https://github.com/MakieOrg/Makie.jl/pull/3713).
 - Added `scale` attribute to `violin` [#3352](https://github.com/MakieOrg/Makie.jl/pull/3352).
 - Use label formatter in barplot [#3718](https://github.com/MakieOrg/Makie.jl/pull/3718).
+- Fix the incorrect shading with non uniform markerscale in meshscatter [#3722](https://github.com/MakieOrg/Makie.jl/pull/3722)
 
 ## [0.20.8] - 2024-02-22
 

CairoMakie/src/primitives.jl

@@ -931,10 +931,11 @@ function draw_mesh3D(
     ctx = screen.context
     projectionview = Makie.space_to_clip(scene.camera, space, true)
     eyeposition = scene.camera.eyeposition[]
-    i = Vec(1, 2, 3)
-    normalmatrix = transpose(inv(model[i, i]))
 
+    i = Vec(1, 2, 3)
     local_model = rotation * Makie.scalematrix(Vec3f(scale))
+    normalmatrix = transpose(inv(model[i, i] * local_model[i, i])) # see issue #3702
+
     # pass transform_func as argument to function, so that we get a function barrier
     # and have `transform_func` be fully typed inside closure
     vs = broadcast(meshpoints, (transform_func,)) do v, f

GLMakie/assets/shader/particles.vert

@@ -100,7 +100,7 @@ void main(){
     o_id = uvec2(objectid, index+1);
     vec3 s = _scale(scale, index);
     vec3 V = vertices * s;
-    vec3 N = normals;
+    vec3 N = normals / s; // see issue #3702
     vec3 pos;
     {{position_calc}}
     o_color = get_particle_color(color, intensity, color_map, color_norm, index, len);

ReferenceTests/src/tests/examples3d.jl

@@ -128,6 +128,13 @@ end
     scatter(RNG.rand(20), RNG.rand(20), markersize=RNG.rand(20) .* 20, color=colors)
 end
 
+@reference_test "Ellipsoid marker sizes" begin # see PR #3722
+    pts = Point3f[[0, 0, 0], [1, 0, 0]]
+    markersize = Vec3f[[0.5, 0.2, 0.5], [0.5, 0.2, 0.5]]
+    rotations = [qrotation(Vec3f(1, 0, 0), 0), qrotation(Vec3f(1, 1, 0), π / 4)]
+    meshscatter(pts; markersize, rotations, color=:white, diffuse=Vec3f(-2, 0, 4), specular=Vec3f(4, 0, -2))
+end
+
 @reference_test "Record Video" begin
     f(t, v, s) = (sin(v + t) * s, cos(v + t) * s, (cos(v + t) + sin(v)) * s)
     t = Observable(0.0) # create a life signal

WGLMakie/assets/particles.vert

@@ -30,7 +30,7 @@ void main(){
     // get_* gets the global inputs (uniform, sampler, position array)
     // those functions will get inserted by the shader creation pipeline
     vec3 vertex_position = get_markersize() * to_vec3(get_position());
-    vec3 N = get_normals();
+    vec3 N = get_normals() / get_markersize(); // see issue #3702
     rotate(get_rotations(), vertex_position, N);
     vertex_position = to_vec3(get_offset()) + vertex_position;
     vec4 position_world = model * vec4(vertex_position, 1);