Generate overloads that accept parameters of type ReadOnlySpan<char> rather than string

[NoahStolk]

Related issue: https://github.com/ImGuiNET/ImGui.NET/issues/397

Allowing to pass ReadOnlySpan<char> instead of string can reduce a lot of memory allocations on the heap. For example, this allocates 32 bytes:

int value = Random.Shared.Next(0, 10000);
ImGui.Text(value.ToString());

Of course, 32 bytes isn't much, but when you are drawing a lot of text, every frame, this quickly adds up to a lot of allocations resulting in many garbage collections.

With this PR it becomes possible to do things like this:

int value = Random.Shared.Next(0, 10000);
value.TryFormat(_charBuffer, out _);
ImGui.Text(_charBuffer.AsSpan());

This doesn't allocate any memory (tested with GC.GetAllocatedBytesForCurrentThread).

I've made changes to the code generator; no manual changes were done to the generated files. I've also tested the Text method with the ReadOnlySpan<char> overload in the ImGui.NET.SampleProgram. Do I need to do any more manual testing? Also, if this gets released, which version number do I pick?

Please let me know if I've missed anything.

[zaafar]

this is amazing!!! just 1 small feedback before i can merge it.

The way this PR does it is not ideal since it's going to break everyones project who is using imgui.net (including mine, author of this lib, etc etc). This is because this PR replaced the old string overloads with the new span ones. IMO, they should be added as an extra set of methods.

Also, in a different PR/Issue, i am thinking of supporting ReadOnlySpan<byte> as well, that will reduce the unnecessary UTF16->UTF8 conversions (basically the following block can be removed). Again, not part of this PR.

                filename_byteCount = Encoding.UTF8.GetByteCount(filename);
                if (filename_byteCount > Util.StackAllocationSizeLimit)
                {
                    native_filename = Util.Allocate(filename_byteCount + 1);
                }
                else
                {
                    byte* native_filename_stackBytes = stackalloc byte[filename_byteCount + 1];
                    native_filename = native_filename_stackBytes;
                }
                int native_filename_offset = Util.GetUtf8(filename, native_filename, filename_byteCount);
                native_filename[native_filename_offset] = 0;

[NoahStolk]

The way this PR does it is not ideal since it's going to break everyones project who is using imgui.net (including mine, author of this lib, etc etc). This is because this PR replaced the old string overloads with the new span ones. IMO, they should be added as an extra set of methods.

Are you sure it's breaking? There is an implicit conversion from string to ReadOnlySpan<char>, so I believe everything should still compile. https://learn.microsoft.com/en-us/dotnet/api/system.string.op_implicit?view=net-7.0

The samples are still compiling and working as expected as well:

[CodingMadness]

functions accepting ReadOnlySpan can accept strings, so its all fine actually.

[zaafar]

sounds good, on the weekend, I am going to test it and then get this merged. thank you!

[NoahStolk]

Hi @zaafar

Do you think we could get this merged soon? Let me know if there's anything I can do to help (like more testing).

[zaafar]

I have released version v1.89.5b since cimgui isn't updated to 1.89.6.

[NoahStolk]

Thanks for the merge! I think I broke the CI because the code generator was updated to .NET 7. Will have a look.

[NoahStolk]

I think this should fix the CI. https://github.com/ImGuiNET/ImGui.NET/pull/408/files