Render hdri in ImGUI Image (in viewport)

[jayanam]

Hi guys,
Im using the docking branch and ImGUI with opengl backend. I am rendering opengl into a framebuffer and then add this to ImGui::Image, work pretty nice:

uint64_t textureID = mFrameBuffer->get_texture();
// I know reinterpret_cast is evil - better solution?
ImGui::Image(reinterpret_cast<void*>(textureID), ImVec2{ mSize.x, mSize.y }, ImVec2{ 0, 1 }, ImVec2{ 1, 0 });

I use a simple directional light fragment shader.

My question is: If you want to light the scene with an hdri (different shader), how can I combine this with the framebuffer? Does someone has an example or can tell me the basic steps, just to be on the right track.

Thx in advance!
Jay

[PathogenDavid]

My question is: If you want to light the scene with an hdri (different shader), how can I combine this with the framebuffer? Does someone has an example or can tell me the basic steps, just to be on the right track.

This strikes me as a question outside of the scope of Dear ImGui. ImGui doesn't care about how you render your scene.

// I know reinterpret_cast is evil - better solution?

This is a sensible use of reinterpret_cast, but it is worth noting that this isn't 32-bit portable if that's something you care about.

[ocornut]

I think the crux of the question is:

If you want to light the scene with an hdri (different shader),

Some answers:

• You can use ImDrawList::AddCallback() to communicate state to your renderer, e.g. add a callback with a data requesting shader change. A game I wrote (https://www.thedragonstrap.com) was entirely rendering via ImDrawList + callback to manipulate shader, blending state.
• Note that there's a helper you might or not use: passing ImDrawCallback_ResetRenderState as a callback is a standardized way of requesting the backend to restore all restore state (shader state). You may do that or restore manually only what you modified using a callback.
• In your own engine (and custom renderer backend), another way is to use ImTextureID to express a higher level concept e.g. a material which bundles a texture and the way to render it.

I know reinterpret_cast is evil - better solution?

Solution is to set your mind free from dogmas :)

worth noting that this isn't 32-bit portable

Hmm.. Nothing strikes me as not portable there?

[jayanam]

Thx for the answers, helps a lot!

Solution is to set your mind free from dogmas :)

Dont worry, my mind is free from them... but I ran into issues for applications compiling for 32/64 bit :-)

[PathogenDavid]

Hmm.. Nothing strikes me as not portable there?

Their texture ID is a uint64_t which has to be truncated to fit into a 32-bit void*

[ocornut]

Oh I see. You can #define ImTextureID uint64_t in your config file to fix it.