GameView Vulkan Impl

[LeonBrands]

Hi,

I am trying to implement Vulkan as an editor for our engine. I am currently trying to create a gameview, but am quite confused as how I should implement this. What is the best approach to render a scene and display it onto an imgui widget? Could someone provide an example please?

[ocornut]

Typically you'd render your game scene in an off-screen texture, and then use that texture in your render.
ImGui uses the opaque ImTextureID type (which is basically a void*) as a mechanism to allow you pass your texture identifiers to functions like ImGui::Image() or ImDrawList::AddImage(). Basically the system will just emit draw batches (vertices + texture id) that your rendering can use.

I suggest to look at the other examples (OpenGL/DX) to understand how ImTextureId are generally handled.

The current renderer in the Vulkan always uses the default font texture for rendering. There is a PR here that fixes it to be on par with the other renderer:
#914

Which is an attempt to use ImTextureId to store a VkDescriptorSet, which appears to be the closest thing to describe a texture in Vulkan world. However if you are building your own engine own Vulkan you may have your own type MyTexture* and then you can store.

The reason the PR above is unmerged is that VkDescriptorSet is always 64-bit and void* on 32-bit architecture is, well, 32-bits so it can't be stored with this mechanism. We need to make a modification to the size of ImTextureId to always be 64-bits. If you are targetting 64-bits (which probably you are) then it's a non-problem and you can merge this code.

[ocornut]

Another approach which is a little more optimal but trickier and less flexible, is to use ImDrawList::AddCallback() and use that callback render your game scene directly in-between the imgui draw calls, if you setup all your render state, including viewport/scissor then restore them.
The vast majority of people just render to an offscreen texture because it is simpler.

Also see:
#984
#1261
#1004

[ghost]

Thanks for this thread! I'm learning both ImGui and OpenGL at the same time and these comments pulled me out of the rabbit hole I got sucked down trying to figure out why the mesh I was rendering was not showing in the second GLFWwindow I had created.

[ocornut]

Closing this thread as answered, even through in the case of Vulkan displaying texture requires the patch of #914 which doesn't work in 32-bits.