Vulkan: Support drawing thin/Bresenham lines on NVIDIA

[PureAsbestos]

Godot version

4.0.1

System information

Windows 10, Vulkan, NVIDIA GeForce GTX 1070

Issue description

Not sure if this is technically a bug, but I consider it a regression introduced in Godot 4 with Vulkan. Line rendering (e.g. with draw_line, Line2D, etc.) relies on the graphics backend, and the default behavior for line rendering is different between OpenGL and Vulkan. OpenGL uses the familiar Bresenham style lines, while Vulkan uses something a bit different.

Even in OpenGL compatibility mode, the lines are drawn in the Vulkan style. The OpenGL behavior was preferable for many use-cases, and is especially important for pixel art games and pixel art editors (which is what I'm making at the moment).

It seems that the best solution to this might be to use VK_EXT_line_rasterization to (optionally?) provide this behavior, though as I understand it there might be some portability issues there (I don't think MoltenVK supports VK_EXT_line_rasterization yet for instance).

Update: this problem does not exist consistently everywhere. This new line-drawing style shows up with my NVIDIA GPU but not with Intel Integrated Graphics, which still uses Bresenham-style lines. It really ought to be consistent across devices.

Steps to reproduce

Use draw_line in Godot 3
Use draw_line in Godot 4 and notice that it looks different

Minimal reproduction project

Godot 3 project:
line-test-3.zip

Godot 4 project:
line-test.zip

[AThousandShips]

Are you talking different lines in 4.0 and 3.x or between Forward+ and compatibility?

[PureAsbestos]

Between 4.0 and 3.x.
Forward+ and Compatibility both use Vulkan style line rendering

[AThousandShips]

That is weird as the compatibility backend is OpenGL, not Vulkan, don't know what it is doing

[AThousandShips]

Unfortunately VK_EXT_line_rasterization is not very widely supported it seems, so not sure how likely this is to be supported, considering relatively minor visual difference

[PureAsbestos]

That is weird as the compatibility backend is OpenGL, not Vulkan, don't know what it is doing

My best guess would be that Compatibility is doing something like translating Vulkan code.

Unfortunately VK_EXT_line_rasterization is not very widely supported it seems, so not sure how likely this is to be supported, considering relatively minor visual difference

It's a shame it's not yet very widely supported. The visual difference may seem minor, but to me and perhaps many others it is essential. I will roll my own line renderer or something rather than settle for this (which is both a pain to do and perhaps significantly less performant).

[dalexeev]

It probably depends on the OS/driver. I can't reproduce this.

Vulkan API 1.3.224 - Forward+ - Using Vulkan Device #0: Intel - Intel(R) UHD Graphics 630 (CML GT2)

1.mp4

---

EDIT: You probably meant thick lines (width > 0):

2.mp4

[PureAsbestos]

Ooh, that's interesting... I thought it was defined behavior in the spec.
No, this happens for me with the default width = -1.0 as well

[dalexeev]

No, this happens for me with the default width = -1.0 as well

This is weird, it works for me correctly for width < 0.

Note that in 3.x this also doesn't work for thick lines (width > 1.001 - see #69851 for details).

[PureAsbestos]

I am going to update my graphics drivers to see if that helps, but it would be a tad odd if the behavior of my app relied on having up-to-date drivers...
I'd also like to try switching the Vulkan device to integrated but not sure how to do that right now.

[dalexeev]

it would be a tad odd if the behavior of my app relied on having up-to-date drivers...

• See also Expose Geometry2D.bresenham_line() method #74714. This is less efficient as you will need to draw pixel by pixel (this method is more useful for Image, BitMap, TileMap).

[PureAsbestos]

Okay, I can confirm the problem still exists with the latest NVIDIA drivers installed.

[PureAsbestos]

With a bit of work I was able to get it to launch with Intel Integrated Graphics, and there it does indeed use Bresenham-style lines...