1.92: Auto convert ImTextureID from ImTextureUserID ?

[ocornut]

I've published (#8465) a dynamic_fonts branch which is expected to get merged in 1-2 months as 1.92. Started asking feature for feedback and expecting people to slowly adopt it.

One problem I couldn't solve cleanly relate to language bindings and binding generators.
I've circled around this topic for a while and couldn't find an ideal solution.

In the new design:

• ImTextureID has been renamed to ImTextureUserID. (the type default to u64 but may be compile-time configurable)
• A new struct called ImTextureID contains a ImTextureUserID among other things.
• This can be mostly transparent for C++ users, as ImTextureID can be constructed from ImTextureUserID:

    ImTextureID(ImTextureUserID tex_user_id) { [....] _TexUserID = tex_user_id; }

• The low-level functions all still use ImTextureID:

void ImGui::Image(ImTextureID user_texture_id, ....);
void ImGui::ImageWithBg(ImTextureID user_texture_id, ....);
bool ImGui::ImageButton(ImTextureID user_texture_id, ....);
void ImDrawList::PushTextureID(ImTextureID user_texture_id);
void ImDrawList::AddImage(ImTextureID user_texture_id, ....);
void ImDrawList::AddImageQuad(ImTextureID user_texture_id, ....);
void ImDrawList::AddImageRounded(ImTextureID user_texture_id, ....);
void ImDrawList::_SetTextureID(ImTextureID texture_id);

Those all those the functions using this type.

It is expected that in 99.9% of case the end-user will want to create a ImTextureID from a ImTextureUserID.

---

My suggestion is that binding generators make this transparent to the user.

So maybe C++ ImGui::Image(ImTextureID user_texture_id, ....); should be generated as C igImage(ImTextureUserID id) and NOT as igImage(ImTextureID id) ?

The implementation of the function (the one-liner C->C++ wrapper) will automatically convert the ImTextureUserID to a ImTextureID thanks to the constructor. So I believe you can solve this by only replacing the type in the function signature.

Do you think dear bindings could implement this?

The branch has #define IMGUI_HAS_TEXTURES if needed to differentiate with/without the feature, so technically if this was implemented it could perfectly be pushed today.

Thanks.

[ocornut]

(please ignore this for now as I'm currently reworking the design)

[ShironekoBen]

No worries - I'd apparently ignored it anyway by virtue of not spotting the notification! ^-^;

But FWIW, replacing the type in the signature should be pretty easy to do. We can also provide Ex-esque versions if necessary should there be any use-cases where the user might actually want to pass an ImTextureID in full.

[ocornut]

I have now pushed a redesign.

Previously in the WIP 1.92 branch:

• ImTextureID -> ImTextureUserID
• ImTextureID == new lightweight struct

Now in WIP 1.92 branch

• ImTextureID not renamed.
• ImTextureRef new lightweight struct.

All functions such as ImGui::Image() now take ImTextureRef.
It is transparent for C++ because ImTextureRef can be constructed from ImTextureID.

FYI

struct ImTextureRef
{
    [...]
    ImTextureData*   _TexData;  //      A texture, generally owned by a ImFontAtlas. Will convert to ImTextureID during render loop, after texture has been uploaded.
    ImTextureID      _TexID;    // _OR_ Low-level backend texture identifier, if already uploaded or created by user/app. Generally provided to e.g. ImGui::Image() calls.
};

---

My suggestion above was a mistake :(
It is required in some important situation to pass full ImTextureRef: e.g. when using custom rect packed into imgui atlas.
Therefore, it is incorrect to make all the functions take the lower-level type.

But it is still true that in 99% case, user will construct ImTextureRef (small struct) from ImTextureID.
Maybe binding can generate a helper function e.g.

static inline ImTextureRef ImTextureRefFromID(ImTextureID tex_id)
{
   ImTextureRef tex_ref; 
   tex_ref._TexData = NULL;
   tex_ref._TexID = tex_id;
   return tex_id;
}

Could it be part of some template?
And ideally, if easy, we inject a comment before ImGui::Image(), ImDrawList::AddImage() to point to that helper.