From efbe9237ccfec335efef8233656d4501184c89cc Mon Sep 17 00:00:00 2001
From: "Matias N. Goldberg" <dark_sylinc@yahoo.com.ar>
Date: Sun, 6 Aug 2023 23:21:58 -0300
Subject: [PATCH] Fix integer underflow when rounding up in VoxelGI

The code wanted to divide and round up:
 - 0 / 64 = 0
 - 63 / 64 = 1
 - 64 / 64 = 1
 - 65 / 64 = 2

However when the dividend was exactly 0 it would underflow and produce
67108864 instead.

This caused TDRs on empty scenes or extremely slow performance

Fix #80286

(cherry picked from commit e783e32108520a4d5b866fc0b28f23cedc3c74f6)
---
 servers/rendering/renderer_rd/environment/gi.cpp | 4 ++--
 1 file changed, 2 insertions(+), 2 deletions(-)

diff --git a/servers/rendering/renderer_rd/environment/gi.cpp b/servers/rendering/renderer_rd/environment/gi.cpp
index db63e2f1a99..eeab7b1848c 100644
--- a/servers/rendering/renderer_rd/environment/gi.cpp
+++ b/servers/rendering/renderer_rd/environment/gi.cpp
@@ -2966,7 +2966,7 @@ void GI::VoxelGIInstance::update(bool p_update_light_instances, const Vector<RID
 						push_constant.cell_offset = mipmaps[i].cell_offset;
 						push_constant.cell_count = mipmaps[i].cell_count;
 
-						int64_t wg_todo = (mipmaps[i].cell_count - 1) / wg_size + 1;
+						int64_t wg_todo = (mipmaps[i].cell_count + wg_size - 1) / wg_size;
 						while (wg_todo) {
 							int64_t wg_count = MIN(wg_todo, wg_limit_x);
 							RD::get_singleton()->compute_list_set_push_constant(compute_list, &push_constant, sizeof(VoxelGIPushConstant));
@@ -2987,7 +2987,7 @@ void GI::VoxelGIInstance::update(bool p_update_light_instances, const Vector<RID
 					push_constant.cell_offset = mipmaps[i].cell_offset;
 					push_constant.cell_count = mipmaps[i].cell_count;
 
-					int64_t wg_todo = (mipmaps[i].cell_count - 1) / wg_size + 1;
+					int64_t wg_todo = (mipmaps[i].cell_count + wg_size - 1) / wg_size;
 					while (wg_todo) {
 						int64_t wg_count = MIN(wg_todo, wg_limit_x);
 						RD::get_singleton()->compute_list_set_push_constant(compute_list, &push_constant, sizeof(VoxelGIPushConstant));