Add renderer readback command contract

src/renderer_api/renderer_api.cpp

@@ -196,6 +196,41 @@ pp::foundation::Status validate_readback_region(TextureDesc desc, ReadbackRegion
     return pp::foundation::Status::success();
 }
 
+pp::foundation::Result<std::uint64_t> readback_byte_size(TextureDesc desc, ReadbackRegion region) noexcept
+{
+    const auto region_status = validate_readback_region(desc, region);
+    if (!region_status.ok()) {
+        return pp::foundation::Result<std::uint64_t>::failure(region_status);
+    }
+
+    const auto bpp = static_cast<std::uint64_t>(bytes_per_pixel(desc.format));
+    if (bpp == 0) {
+        return pp::foundation::Result<std::uint64_t>::failure(
+            pp::foundation::Status::invalid_argument("texture format is not supported"));
+    }
+
+    const auto width = static_cast<std::uint64_t>(region.width);
+    const auto height = static_cast<std::uint64_t>(region.height);
+    if (width > std::numeric_limits<std::uint64_t>::max() / height) {
+        return pp::foundation::Result<std::uint64_t>::failure(
+            pp::foundation::Status::out_of_range("readback pixel count overflows uint64"));
+    }
+
+    const auto pixels = width * height;
+    if (pixels > std::numeric_limits<std::uint64_t>::max() / bpp) {
+        return pp::foundation::Result<std::uint64_t>::failure(
+            pp::foundation::Status::out_of_range("readback byte size overflows uint64"));
+    }
+
+    const auto bytes = pixels * bpp;
+    if (bytes > max_texture_bytes) {
+        return pp::foundation::Result<std::uint64_t>::failure(
+            pp::foundation::Status::out_of_range("readback byte size exceeds the configured limit"));
+    }
+
+    return pp::foundation::Result<std::uint64_t>::success(bytes);
+}
+
 const char* texture_format_name(TextureFormat format) noexcept
 {
     switch (format) {