Emulate double precision for regular rendering operation.

We calculate the lost precision on the CPU and pass it into the GPU
so that it can calculate an error-corrected version of the vertex position

2 files changed, 18 insertions, 0 deletions

diff --git a/servers/rendering/renderer_rd/storage_rd/material_storage.h b/servers/rendering/renderer_rd/storage_rd/material_storage.h
index db2e4cfa2a..2ce6550cc1 100644
--- a/servers/rendering/renderer_rd/storage_rd/material_storage.h
+++ b/servers/rendering/renderer_rd/storage_rd/material_storage.h
@@ -311,6 +311,18 @@ public:
 		}
 	}
 
+	// http://andrewthall.org/papers/df64_qf128.pdf
+#ifdef REAL_T_IS_DOUBLE
+	static _FORCE_INLINE_ void split_double(double a, float *ahi, float *alo) {
+		const double SPLITTER = (1 << 29) + 1;
+		double t = a * SPLITTER;
+		double thi = t - (t - a);
+		double tlo = a - thi;
+		*ahi = (float)thi;
+		*alo = (float)tlo;
+	}
+#endif
+
 	/* Samplers */
 
 	_FORCE_INLINE_ RID sampler_rd_get_default(RS::CanvasItemTextureFilter p_filter, RS::CanvasItemTextureRepeat p_repeat) {
diff --git a/servers/rendering/renderer_rd/storage_rd/render_scene_data_rd.cpp b/servers/rendering/renderer_rd/storage_rd/render_scene_data_rd.cpp
index f925f87cbe..7dd790d1da 100644
--- a/servers/rendering/renderer_rd/storage_rd/render_scene_data_rd.cpp
+++ b/servers/rendering/renderer_rd/storage_rd/render_scene_data_rd.cpp
@@ -59,6 +59,12 @@ void RenderSceneDataRD::update_ubo(RID p_uniform_buffer, RS::ViewportDebugDraw p
 	RendererRD::MaterialStorage::store_transform(cam_transform, ubo.inv_view_matrix);
 	RendererRD::MaterialStorage::store_transform(cam_transform.affine_inverse(), ubo.view_matrix);
 
+#ifdef REAL_T_IS_DOUBLE
+	RendererRD::MaterialStorage::split_double(-cam_transform.origin.x, &ubo.inv_view_matrix[12], &ubo.inv_view_matrix[3]);
+	RendererRD::MaterialStorage::split_double(-cam_transform.origin.y, &ubo.inv_view_matrix[13], &ubo.inv_view_matrix[7]);
+	RendererRD::MaterialStorage::split_double(-cam_transform.origin.z, &ubo.inv_view_matrix[14], &ubo.inv_view_matrix[11]);
+#endif
+
 	for (uint32_t v = 0; v < view_count; v++) {
 		projection = correction * view_projection[v];
 		RendererRD::MaterialStorage::store_camera(projection, ubo.projection_matrix_view[v]);