From bbc5ba3050076e326b9f9d1b3769e85518f8ae1c Mon Sep 17 00:00:00 2001
From: Imbris <imbrisf@gmail.com>
Date: Mon, 3 May 2021 22:13:40 -0400
Subject: [PATCH] [rs] Skip mapping of zero sized buffers in create_buffer_init
 to avoid a panic and avoid creating an unused padded buffer

---
 wgpu/src/util/device.rs | 60 +++++++++++++++++++++++++----------------
 1 file changed, 37 insertions(+), 23 deletions(-)

diff --git a/wgpu/src/util/device.rs b/wgpu/src/util/device.rs
index 2c7f4c93e7..fd9f3c77d6 100644
--- a/wgpu/src/util/device.rs
+++ b/wgpu/src/util/device.rs
@@ -36,29 +36,43 @@ pub trait DeviceExt {
 
 impl DeviceExt for crate::Device {
     fn create_buffer_init(&self, descriptor: &BufferInitDescriptor<'_>) -> crate::Buffer {
-        let unpadded_size = descriptor.contents.len() as crate::BufferAddress;
-        // Valid vulkan usage is
-        // 1. buffer size must be a multiple of COPY_BUFFER_ALIGNMENT.
-        // 2. buffer size must be greater than 0.
-        // Therefore we round the value up to the nearest multiple, and ensure it's at least COPY_BUFFER_ALIGNMENT.
-        let align_mask = crate::COPY_BUFFER_ALIGNMENT - 1;
-        let padded_size =
-            ((unpadded_size + align_mask) & !align_mask).max(crate::COPY_BUFFER_ALIGNMENT);
-
-        let wgt_descriptor = crate::BufferDescriptor {
-            label: descriptor.label,
-            size: padded_size,
-            usage: descriptor.usage,
-            mapped_at_creation: true,
-        };
-
-        let buffer = self.create_buffer(&wgt_descriptor);
-        buffer
-            .slice(..unpadded_size)
-            .get_mapped_range_mut()
-            .copy_from_slice(descriptor.contents);
-        buffer.unmap();
-        buffer
+        // Skip mapping if the buffer is zero sized
+        if descriptor.contents.is_empty() {
+            let wgt_descriptor = crate::BufferDescriptor {
+                label: descriptor.label,
+                size: 0,
+                usage: descriptor.usage,
+                mapped_at_creation: false,
+            };
+
+            self.create_buffer(&wgt_descriptor)
+        } else {
+            let unpadded_size = descriptor.contents.len() as crate::BufferAddress;
+            // Valid vulkan usage is
+            // 1. buffer size must be a multiple of COPY_BUFFER_ALIGNMENT.
+            // 2. buffer size must be greater than 0.
+            // Therefore we round the value up to the nearest multiple, and ensure it's at least COPY_BUFFER_ALIGNMENT.
+            let align_mask = crate::COPY_BUFFER_ALIGNMENT - 1;
+            let padded_size =
+                ((unpadded_size + align_mask) & !align_mask).max(crate::COPY_BUFFER_ALIGNMENT);
+
+            let wgt_descriptor = crate::BufferDescriptor {
+                label: descriptor.label,
+                size: padded_size,
+                usage: descriptor.usage,
+                mapped_at_creation: true,
+            };
+
+            let buffer = self.create_buffer(&wgt_descriptor);
+
+            buffer
+                .slice(..unpadded_size)
+                .get_mapped_range_mut()
+                .copy_from_slice(descriptor.contents);
+            buffer.unmap();
+
+            buffer
+        }
     }
 
     fn create_texture_with_data(