Extract canvas projection helpers and thin preview and node loading

src/legacy_canvas_projection_services.h

@@ -0,0 +1,26 @@
+#pragma once
+
+#include "canvas_modes.h"
+#include "util.h"
+
+class Canvas;
+
+namespace pp::panopainter {
+
+bool legacy_canvas_point_trace(Canvas& canvas, glm::vec2 loc, glm::vec3& ray_origin, glm::vec3& ray_dir,
+    glm::vec3& hit_pos, glm::vec2& fb_pos, glm::vec3& hit_normal, int& out_plane_id);
+bool legacy_canvas_point_trace_plane(Canvas& canvas, glm::vec2 loc, glm::vec3& ray_origin, glm::vec3& ray_dir,
+    glm::vec3& hit_pos, glm::vec3& hit_normal, glm::vec2& hit_fb_pos, int plane_id);
+void legacy_canvas_point_unproject(glm::vec2 loc, glm::vec4 vp, glm::mat4 camera, glm::mat4 proj,
+    glm::vec3& out_origin, glm::vec3& out_dir);
+void legacy_canvas_point_unproject(Canvas& canvas, glm::vec2 loc, glm::vec3& out_origin, glm::vec3& out_dir);
+glm::vec3 legacy_canvas_point_trace(Canvas& canvas, glm::vec2 loc);
+void legacy_canvas_project_2d_points(Canvas& canvas, std::vector<vertex_t>& vertices);
+glm::vec3 legacy_canvas_project_2d_point(Canvas& canvas, glm::vec2 pt);
+std::vector<glm::vec2> legacy_canvas_face_to_shape_2d(const Canvas& canvas, int plane_index);
+void legacy_canvas_push_camera(Canvas& canvas);
+void legacy_canvas_pop_camera(Canvas& canvas);
+CameraData legacy_canvas_get_camera(const Canvas& canvas);
+void legacy_canvas_set_camera(Canvas& canvas, const CameraData& camera);
+
+} // namespace pp::panopainter