Sokol: "Multi-window support" brain dump

[floooh]

What's needed to add "proper" multi-window support to sokol_gfx.h and sokol_app.h:

sokol_gfx.h:
Not strictly multi-window specific, but sg_desc needs a couple more parameters to describe the default framebuffer, this is only needed for validation whether a pipeline object is compatible with that pass:

• color and depth pixel formats
• sample count

sg_setup_context() needs a sg_contect_desc* param which contains swap-chain / context-specific parameters (a subset of what's in sg_desc):

    const void* (*mtl_renderpass_descriptor_cb)(void);
    const void* (*mtl_drawable_cb)(void);
    const void* (*d3d11_render_target_view_cb)(void);
    const void* (*d3d11_depth_stencil_view_cb)(void);

...plus the color/depth pixel formats and sample count.

The callbacks are needed because each window has its own swap chain. The pixel formats and sample count are needed for pipeline validation.

Then, for each window call sg_setup_context(), and before the default render pass of that window, call sg_activate_context().

sokol_app.h:

This will be much more work:

• provide max number of windows in sapp_desc to allocate "window pool"
• sapp_window handle type (same as the sokol-gfx handles)
• the "main window" gets a special default handle
• each window needs its own swap chain / GL context
• sapp_event needs the window handle, to associate events with windows
• new sapp_window_width/height() functions which take a window handle
• sapp_create_window() / sapp_destroy_window()
• sapp_show_window() / sapp_hide_window()
• sapp_minimize_window() / sapp_maximize_window() / sapp_restore_window()
• sapp_resize_window()?
• ...when in doubt, look how GLFW solves it :)

[incrediblejr]

A proof of concept implementation can be found here with the test file here which creates multiple windows, each using sokol gfx.

This is by no means complete and should seen as a way to get the ball rolling / discussions started. It is currently only working on Windows with D3D11.

Please refer to the comments (make a diff to master to see what changed) in the sokol_app.h + sokol_gfx.h. As I do not know the limitations/quirks of the non-Windows platforms supported by sokol app/gfx input _and_ help is needed to take this further.

[icefoxen]

Personally as a user I would far prefer sokol_app.h stays simple and only supports one window, rather than adding a bunch of complexity for a big feature that often won't be used. I'm only using it for gamedev though, so I'm biased.

[medvednikov]

For me this is very important since I wanted to use Sokol as a backend for a UI engine.

It's not possible, until this is implemented.

[ikrima]

_(For posterity, posting here as well)_

ImGui multiviewport integration:

Demo: https://twitter.com/ikrimae/status/1252194400681127936
Repo: https://github.com/ikrima/sokol

• Integrated with ImGui 1.76's docking branch
• Updated/fixed from @incrediblejr proof of concept
• Windows & DX11
• Hasitly put together (aka hacky shortcuts abound); will cleanup possibly

[septag]

This is impressive. can't wait for multi-view + imgui support on the official repo

[kattkieru]

Curious about the state of this, whether or not the plan includes multi-window iOS support?

[ikrima]

@kattkieru I just merged & updated my fork (https://github.com/ikrima/sokol) to the latest. It's mostly updated to be idiomatic with the rest of sokol

Having that said, some caveats

• merged 6+mo of commits in one setting so bugs probably
• probably even more so with new features since I haven't used them yet
• I only bothered to migrate the win32/d3d path

But given some of the changes in sokol like user context data/etc, it's a bit more feasible to merge into main + add other platforms (cc: @floooh )

It still needs a decent cleanup pass tho since I usually just hack whatever my pressing need is

[floooh]

Thanks for the headsup. I'll need to set aside a bit of time to play around and get familiar with your fork and my year-end vacation is coming up. It'll most likely slip into the next year.

[ikrima]

No rush! Only tagged you for your curiosity; fork isn't really in a good PR ready form + cleaning up some old outstanding bugs. Probably will be till next year before i fully sanitize it as well

[kattkieru]

@ikrima Excellent timing, as I'm looking at this again for my christmas break. Thanks for posting!

[stbachmann]

@ikrima @kattkieru I've opened a new pull-request that has a more complete multi-window implementation (using some of the previous work done here already): https://github.com/floooh/sokol/pull/437

Happy to hear thoughts/feedback!

[ikrima]

@stbachmann excellent. Don't have too much time right now to dive into it but from quick scan, the only thing that sticks out is updating the sokol imgui bits.

There's a bug in the imgui shader bc it doesn't scale the vtx position according to the window clipspace (imgui emits in absolute window space in multiviewport mode). Here's the updated shader:

@module _simgui

@vs vs
uniform vs_params {
  vec4 disp_rect;
};
in vec2 position;
in vec2 texcoord0;
in vec4 color0;
out vec2 uv;
out vec4 color;
void main() {
  gl_Position = vec4((((position-disp_rect.xy)/disp_rect.zw)-0.5)*vec2(2.0,-2.0), 0.5, 1.0);
  uv = texcoord0;
  color = color0;
}
@end

@fs fs
uniform sampler2D tex;
in vec2 uv;
in vec4 color;
out vec4 frag_color;
void main() {
  frag_color = texture(tex, uv) * color;
}
@end

@program simgui vs fs

[stbachmann]

@ikrima thanks, great pointer. I'll check out what you did on your branch to make this work. 👍

[ylluminate]

As mentioned before by @medvednikov this is necessary for V lang's (>21k stars) fantastic V UI library. Highly compelling.