Fixes broken CPUParticles2D AtlasTextures usage

(cherry picked from commit 36d9906d6a5af1913033f3d0a1adcef387201c61)

scene/2d/cpu_particles_2d.cpp

@@ -29,7 +29,7 @@
 /*************************************************************************/
 
 #include "cpu_particles_2d.h"
-
+#include "core/core_string_names.h"
 #include "scene/2d/canvas_item.h"
 #include "scene/2d/particles_2d.h"
 #include "scene/resources/particles_material.h"
@@ -169,10 +169,20 @@ void CPUParticles2D::_update_mesh_texture() {
 	vertices.push_back(-tex_size * 0.5 + Vector2(tex_size.x, tex_size.y));
 	vertices.push_back(-tex_size * 0.5 + Vector2(0, tex_size.y));
 	PoolVector<Vector2> uvs;
-	uvs.push_back(Vector2(0, 0));
-	uvs.push_back(Vector2(1, 0));
-	uvs.push_back(Vector2(1, 1));
-	uvs.push_back(Vector2(0, 1));
+	AtlasTexture *atlas_texure = Object::cast_to<AtlasTexture>(*texture);
+	if (atlas_texure && atlas_texure->get_atlas().is_valid()) {
+		Rect2 region_rect = atlas_texure->get_region();
+		Size2 atlas_size = atlas_texure->get_atlas()->get_size();
+		uvs.push_back(Vector2(region_rect.position.x / atlas_size.x, region_rect.position.y / atlas_size.y));
+		uvs.push_back(Vector2((region_rect.position.x + region_rect.size.x) / atlas_size.x, region_rect.position.y / atlas_size.y));
+		uvs.push_back(Vector2((region_rect.position.x + region_rect.size.x) / atlas_size.x, (region_rect.position.y + region_rect.size.y) / atlas_size.y));
+		uvs.push_back(Vector2(region_rect.position.x / atlas_size.x, (region_rect.position.y + region_rect.size.y) / atlas_size.y));
+	} else {
+		uvs.push_back(Vector2(0, 0));
+		uvs.push_back(Vector2(1, 0));
+		uvs.push_back(Vector2(1, 1));
+		uvs.push_back(Vector2(0, 1));
+	}
 	PoolVector<Color> colors;
 	colors.push_back(Color(1, 1, 1, 1));
 	colors.push_back(Color(1, 1, 1, 1));
@@ -198,12 +208,29 @@ void CPUParticles2D::_update_mesh_texture() {
 }
 
 void CPUParticles2D::set_texture(const Ref<Texture> &p_texture) {
+	if (p_texture == texture)
+		return;
+
+	if (texture.is_valid())
+		texture->disconnect(CoreStringNames::get_singleton()->changed, this, "_texture_changed");
 
 	texture = p_texture;
+
+	if (texture.is_valid())
+		texture->connect(CoreStringNames::get_singleton()->changed, this, "_texture_changed");
+
 	update();
 	_update_mesh_texture();
 }
 
+void CPUParticles2D::_texture_changed() {
+
+	if (texture.is_valid()) {
+		update();
+		_update_mesh_texture();
+	}
+}
+
 Ref<Texture> CPUParticles2D::get_texture() const {
 
 	return texture;
@@ -1315,6 +1342,7 @@ void CPUParticles2D::_bind_methods() {
 	ClassDB::bind_method(D_METHOD("convert_from_particles", "particles"), &CPUParticles2D::convert_from_particles);
 
 	ClassDB::bind_method(D_METHOD("_update_render_thread"), &CPUParticles2D::_update_render_thread);
+	ClassDB::bind_method(D_METHOD("_texture_changed"), &CPUParticles2D::_texture_changed);
 
 	ADD_GROUP("Emission Shape", "emission_");
 	ADD_PROPERTY(PropertyInfo(Variant::INT, "emission_shape", PROPERTY_HINT_ENUM, "Point,Sphere,Box,Points,Directed Points"), "set_emission_shape", "get_emission_shape");

scene/2d/cpu_particles_2d.h

@@ -186,6 +186,8 @@ private:
 
 	void _set_redraw(bool p_redraw);
 
+	void _texture_changed();
+
 protected:
 	static void _bind_methods();
 	void _notification(int p_what);