Fix the calculation and validation of layer and mip ranges in create_…

…texture_view.

The previous code was doing "selector.layers = base_layer .. count" instead of "base_layer .. base_layer + count" which looked dubious. Same thing for the mip range. It was also not taking the base layer count when in requested_layer_count when the texture was not a texture array which led to invalid ranges and underflow when asking for a non-zero base layer with a (non-array) 2d texture.

wgpu-core/src/device/mod.rs

@@ -948,18 +948,21 @@ impl<A: HalApi> Device<A> {
             },
         };
 
-        let required_level_count =
-            desc.range.base_mip_level + desc.range.mip_level_count.map_or(1, |count| count.get());
+        let mip_count = desc.range.mip_level_count.map_or(1, |count| count.get());
+        let required_level_count = desc.range.base_mip_level.saturating_add(mip_count);
+
         let required_layer_count = match desc.range.array_layer_count {
-            Some(count) => desc.range.base_array_layer + count.get(),
+            Some(count) => desc.range.base_array_layer.saturating_add(count.get()),
             None => match view_dim {
                 wgt::TextureViewDimension::D1
                 | wgt::TextureViewDimension::D2
                 | wgt::TextureViewDimension::D3 => 1,
                 wgt::TextureViewDimension::Cube => 6,
                 _ => texture.desc.array_layer_count(),
-            },
+            }
+            .max(desc.range.base_array_layer.saturating_add(1)),
         };
+
         let level_end = texture.full_range.mips.end;
         let layer_end = texture.full_range.layers.end;
         if required_level_count > level_end {