Fix 2D Particle velocity with directed emission mask

Changed CPU velocity calculation for EMISSION_SHAPE_DIRECTED_POINTS
to follow the same logic as in the GPU version:
mat2 rotm;
rotm[0] = texelFetch(emission_texture_normal, emission_tex_ofs, 0).xy;
rotm[1] = rotm[0].yx * vec2(1.0, -1.0);
VELOCITY.xy = rotm * VELOCITY.xy;

Now both CPUParticles2D & CPUParticles3D (z disabled) show the same results
as their GPU counterparts and take the initial velocity settings into account.

1 files changed, 9 insertions, 7 deletions

diff --git a/scene/3d/cpu_particles_3d.cpp b/scene/3d/cpu_particles_3d.cpp
index 4244a11592..ad8760251f 100644
--- a/scene/3d/cpu_particles_3d.cpp
+++ b/scene/3d/cpu_particles_3d.cpp
@@ -726,13 +726,15 @@ void CPUParticles3D::_particles_process(float p_delta) {
 
 					if (emission_shape == EMISSION_SHAPE_DIRECTED_POINTS && emission_normals.size() == pc) {
 						if (flags[FLAG_DISABLE_Z]) {
-							/*
-							mat2 rotm;
-							";
-									rotm[0] = texelFetch(emission_texture_normal, emission_tex_ofs, 0).xy;
-							rotm[1] = rotm[0].yx * vec2(1.0, -1.0);
-							VELOCITY.xy = rotm * VELOCITY.xy;
-							*/
+							Vector3 normal = emission_normals.get(random_idx);
+							Vector2 normal_2d(normal.x, normal.y);
+							Transform2D m2;
+							m2.set_axis(0, normal_2d);
+							m2.set_axis(1, normal_2d.tangent());
+							Vector2 velocity_2d(p.velocity.x, p.velocity.y);
+							velocity_2d = m2.basis_xform(velocity_2d);
+							p.velocity.x = velocity_2d.x;
+							p.velocity.y = velocity_2d.y;
 						} else {
 							Vector3 normal = emission_normals.get(random_idx);
 							Vector3 v0 = Math::abs(normal.z) < 0.999 ? Vector3(0.0, 0.0, 1.0) : Vector3(0, 1.0, 0.0);