Calculate the viewport location correctly in OpenXR

Fixes #104193

In OpenXR the viewport location is not centered on the transform origin

Author: jamie-pate

modules/raycast/raycast_occlusion_cull.cpp

@@ -525,14 +525,14 @@ void RaycastOcclusionCull::buffer_set_size(RID p_buffer, const Vector2i &p_size)
 	buffers[p_buffer].resize(p_size);
 }
 
-Vector2 RaycastOcclusionCull::_jitter_half_extents(const Vector2 &p_half_extents, const Size2i &p_viewport_size) {
+Vector2 RaycastOcclusionCull::_get_jitter(const Rect2 &p_viewport_rect, const Size2i &p_buffer_size) {
 	if (!_jitter_enabled) {
-		return p_half_extents;
+		return Vector2();
 	}
 
 	// Prevent divide by zero when using NULL viewport.
-	if ((p_viewport_size.x <= 0) || (p_viewport_size.y <= 0)) {
-		return p_half_extents;
+	if ((p_buffer_size.x <= 0) || (p_buffer_size.y <= 0)) {
+		return Vector2();
 	}
 
 	int32_t frame = Engine::get_singleton()->get_frames_drawn();
@@ -568,8 +568,8 @@ Vector2 RaycastOcclusionCull::_jitter_half_extents(const Vector2 &p_half_extents
 			jitter = Vector2(0.5f, 0.5f);
 		} break;
 	}
-
-	jitter *= Vector2(p_half_extents.x / (float)p_viewport_size.x, p_half_extents.y / (float)p_viewport_size.y);
+	Vector2 half_extents = p_viewport_rect.get_size() * 0.5;
+	jitter *= Vector2(half_extents.x / (float)p_buffer_size.x, half_extents.y / (float)p_buffer_size.y);
 
 	// The multiplier here determines the jitter magnitude in pixels.
 	// It seems like a value of 0.66 matches well the above jittering pattern as it generates subpixel samples at 0, 1/3 and 2/3
@@ -578,7 +578,16 @@ Vector2 RaycastOcclusionCull::_jitter_half_extents(const Vector2 &p_half_extents
 	// False shown can lower percentage that are occluded, and therefore performance.
 	jitter *= 0.66f;
 
-	return p_half_extents + jitter;
+	return jitter;
+}
+
+Rect2 _get_viewport_rect(const Projection &p_cam_projection) {
+	// NOTE: This assumes a rectangular projection plane, i.e. that:
+	// - the matrix is a projection across z-axis (i.e. is invertible and columns[0][1], [0][3], [1][0] and [1][3] == 0)
+	// - the projection plane is rectangular (i.e. columns[0][2] and [1][2] == 0 if columns[2][3] != 0)
+	Size2 half_extents = p_cam_projection.get_viewport_half_extents();
+	Point2 bottom_left = -half_extents * Vector2(p_cam_projection.columns[3][0] * p_cam_projection.columns[3][3] + p_cam_projection.columns[2][0] * p_cam_projection.columns[2][3] + 1, p_cam_projection.columns[3][1] * p_cam_projection.columns[3][3] + p_cam_projection.columns[2][1] * p_cam_projection.columns[2][3] + 1);
+	return Rect2(bottom_left, 2 * half_extents);
 }
 
 void RaycastOcclusionCull::buffer_update(RID p_buffer, const Transform3D &p_cam_transform, const Projection &p_cam_projection, bool p_cam_orthogonal) {
@@ -595,11 +604,12 @@ void RaycastOcclusionCull::buffer_update(RID p_buffer, const Transform3D &p_cam_
 	Scenario &scenario = scenarios[buffer.scenario_rid];
 	scenario.update();
 
-	Vector2 viewport_half = p_cam_projection.get_viewport_half_extents();
-	Vector2 jitter_viewport_half = _jitter_half_extents(viewport_half, buffer.get_occlusion_buffer_size());
-	Vector3 near_bottom_left = Vector3(-jitter_viewport_half.x, -jitter_viewport_half.y, -p_cam_projection.get_z_near());
+	Rect2 vp_rect = _get_viewport_rect(p_cam_projection);
+	Vector2 bottom_left = vp_rect.position;
+	bottom_left += _get_jitter(vp_rect, buffer.get_occlusion_buffer_size());
+	Vector3 near_bottom_left = Vector3(bottom_left.x, bottom_left.y, -p_cam_projection.get_z_near());
 
-	buffer.update_camera_rays(p_cam_transform, near_bottom_left, 2 * viewport_half, p_cam_projection.get_z_far(), p_cam_orthogonal);
+	buffer.update_camera_rays(p_cam_transform, near_bottom_left, vp_rect.get_size(), p_cam_projection.get_z_far(), p_cam_orthogonal);
 
 	scenario.raycast(buffer.camera_rays, buffer.camera_ray_masks.ptr(), buffer.camera_rays_tile_count);
 	buffer.sort_rays(-p_cam_transform.basis.get_column(2), p_cam_orthogonal);

modules/raycast/raycast_occlusion_cull.h

@@ -161,7 +161,7 @@ class RaycastOcclusionCull : public RendererSceneOcclusionCull {
 	bool _jitter_enabled = false;
 
 	void _init_embree();
-	Vector2 _jitter_half_extents(const Vector2 &p_half_extents, const Size2i &p_viewport_size);
+	Vector2 _get_jitter(const Rect2 &p_viewport_rect, const Size2i &p_buffer_size);
 
 public:
 	virtual bool is_occluder(RID p_rid) override;