Font Rendering on Intel iGPU

[msprengholz]

Hi,

when running the app on my rather old Intel iGPU (HD 620) the font is not rendered correctly. See the image below:

When resizing the UI it sometimes becomes clearly readable, but only for a few seconds.

Everything apart from that seems to work: images of the example shaders are displayed correctly and the shaders themselves also appear to work fine.

In commit 808d769 the requirement for the Vulkan ray tracing extension was lifted. I also had to set the VK_KHR_FRAGMENT_SHADER_BARYCENTRIC_EXTENSION_NAME to not be required for the app to launch on the iGPU. For this I edited line 265 in src/sample_gui.cpp:
{.extensionName = VK_KHR_FRAGMENT_SHADER_BARYCENTRIC_EXTENSION_NAME, .feature = &barycentricFeatures, .required = false},

There is one example shader that should display a wireframe mesh, but I only get a black object instead. I guess this has to do with disabling the shader extension.
Could disabling the extension also have influenced the font rendering? Or is this issue unrelated to that?

[NBickford-NV]

Hi @msprengholz , thanks for reporting this!

I think the font rendering issue is probably unrelated; ImGui uses its own render pipelines and shaders, which use basic Vulkan. However, nvpro_core2 uses a version of ImGui only a few weeks after dynamic font scaling was added to ImGui, so maybe there's a bug there?

Out of curiosity, could you try building https://github.com/nvpro-samples/vk_order_independent_transparency/ (or let me know if you'd like a pre-built version), then resizing it or changing your monitor display scale; do you see the same font rendering issue?

For the barycentric extension, that extension's indeed required for the Basics/Wireframe.slang example, since it uses SV_Barycentrics. That does suggest a good idea, though, which I'll definitely need once I add ray tracing support and which could also be used for barycentrics: the app could check which extensions are available and only enable those Slang capabilities supported on the current system. Then we'd get a proper error message instead of a black screen/validation error if the shader features aren't available. (Even better would be if we could compile the shader, then check which capabilities were used after the fact; I'm not 100% sure this is possible, but I'll check when working on this).

Thanks again!

[msprengholz]

I built the vk_order_independent_transparency example and I see the same font rendering issue. Resizing the window and changing the display scale do not change anything here. I also tried the same approach on the vk_slang_editor. There, setting the display scale to 150% or higher seemed to influence if the text was legible on startup. But it always returned to being garbled once I interacted with the editor or resized the window. I am on Linux running Gnome on Wayland. I could try building the editor on Windows on the same hardware to see if the error exists there as well.

P.S.: To build vk_order_independent_transparency I had to edit the CMake file. It still looks for the master branch on the GitHub repo, which is now named main.

[NBickford-NV]

Thanks @msprengholz ! I bet it's the same issue as ocornut/imgui#8801 -- nvpro_core2's using a version of ImGui from just a few weeks before the fix, so I bet if we update that it'll get fixed. I'll update here again once it's available to test!