More correctly divide alpha by 8 for mipmaps, fixes voxel overocclusion.

servers/visual/rasterizer_rd/rasterizer_scene_rd.cpp

@@ -1948,7 +1948,7 @@ void RasterizerSceneRD::gi_probe_update(RID p_probe, bool p_update_light_instanc
 				push_constant.prev_rect_ofs[1] = 0;
 				push_constant.prev_rect_size[0] = 0;
 				push_constant.prev_rect_size[1] = 0;
-				push_constant.keep_downsample_color = true;
+				push_constant.on_mipmap = false;
 
 				//process lighting
 				RD::ComputeListID compute_list = RD::get_singleton()->compute_list_begin();
@@ -2005,7 +2005,7 @@ void RasterizerSceneRD::gi_probe_update(RID p_probe, bool p_update_light_instanc
 					push_constant.prev_rect_size[1] = push_constant.rect_size[1];
 					push_constant.rect_size[0] = rect.size[0];
 					push_constant.rect_size[1] = rect.size[1];
-					push_constant.keep_downsample_color = gi_probe->dynamic_maps[k].mipmap <= 0;
+					push_constant.on_mipmap = gi_probe->dynamic_maps[k].mipmap > 0;
 
 					RD::get_singleton()->compute_list_add_barrier(compute_list);
 

servers/visual/rasterizer_rd/rasterizer_scene_rd.h

@@ -173,7 +173,7 @@ private:
 		uint32_t flip_x;
 		uint32_t flip_y;
 		float dynamic_range;
-		uint32_t keep_downsample_color;
+		uint32_t on_mipmap;
 	};
 
 	struct GIProbeInstance {

servers/visual/rasterizer_rd/shaders/giprobe.glsl

@@ -134,7 +134,7 @@ layout (r16ui,set=0,binding=7) uniform restrict writeonly uimage3D aniso_neg_tex
 layout(push_constant, binding = 0, std430) uniform Params {
 
 	ivec3 limits;
-	uint light_count;
+	uint light_count; //when not lighting
 	ivec3 x_dir;
 	float z_base;
 	ivec3 y_dir;
@@ -148,7 +148,7 @@ layout(push_constant, binding = 0, std430) uniform Params {
 	bool flip_x;
 	bool flip_y;
 	float dynamic_range;
-	bool keep_downsample_color;
+	bool on_mipmap;
 
 } params;
 
@@ -753,7 +753,7 @@ void main() {
 		}
 
 
-		accum/=4.0;
+		accum/=params.on_mipmap ? 8.0 : 4.0;
 
 		if (count==0.0) {
 			accum_z=0.0; //avoid nan