Add background image support for OpenGL

[yunusey]

Partially fixes #3645.

Ghostty.Background.Image.Demo.Scaled.mp4

I apologize for the video quality - GitHub limits videos to be less than 10MB.

This PR adds support for setting background image dynamically for OpenGL only. Metal still needs its own implementation.

Because the only way to read the image data and decode to RGB/RGBA so that it is ready to be uploaded to the GPU is to use kitty.terminal.graphics with the project's current state, we only support PNG.

[jcollie]

This is starting to look very good! I'm sure others will have more to say about the rendering code as they have more experience, but I like it!

[mitchellh]

Fantastic work. I've left some review comments but overall this is looking good.

[jcollie]

This is looking good to me!

[yunusey]

@mitchellh, could you take a look at this? Are there any other changes needed here, or is it ready to go?

[jarodtaylor]

Ohhhh I can't wait for this to get in!

[sagg0t]

Amazing work here, thank you very much!

And though it's kinda late to ask for such changes may I suggest another option for background-image-mode.
The reason being is that of all the modes implemented so far, if I want an image to fill my whole screen, I'm pretty much choosing between "scaled" mode, which deforms the image or "zoomed" mode, which leaves parts of the window uncovered by the image. And I personally don't find any of those aesthetically pleasing.

The way it should work is that the image is placed in the center, scaled to fill all the window background while preserving aspect ratio, and if the aspect ratio of the image doesn't match one of the terminal window, the part of the image that exceeds the window gets cut off (maybe name it "cropped" mode.)

For reference I can suggest MacOS wallpaper modes:

• "zoomed" mode would be "Fit to Screen";
• "scaled" mode would be "Stretch to Fill Screen";
• and what I'm suggesting is "Fill screen".

I know it's a lot and I'd gladly implement it myself, but I'm barely familiar with Zig and have zero experience with shaders.
So please consider.

[yunusey]

Amazing work here, thank you very much!

Thank you so much!

And though it's kinda late to ask for such changes may I suggest another option for background-image-mode. The reason being is that of all the modes implemented so far, if I want an image to fill my whole screen, I'm pretty much choosing between "scaled" mode, which deforms the image or "zoomed" mode, which leaves parts of the window uncovered by the image. And I personally don't find any of those aesthetically pleasing.

The way it should work is that the image is placed in the center, scaled to fill all the window background while preserving aspect ratio, and if the aspect ratio of the image doesn't match one of the terminal window, the part of the image that exceeds the window gets cut off (maybe name it "cropped" mode.)

I think that's a pretty nice mode. I've just implemented it, and as you requested, the mode's name is cropped. In order to use it, assuming you are on MacOS from your comment, you will probably need to wait until the same feature is implemented for Metal, which MacOS uses. @Rohit-Bevinahally probably will take care of that as well!

Here is a video demonstrating how the mode acts when the terminal is resized:

Ghostty.Cropped.Mode.mp4

The video quality is pretty bad, but hope is sufficient for demonstration purposes.

I know it's a lot and I'd gladly implement it myself, but I'm barely familiar with Zig and have zero experience with shaders.
So please consider.

Thanks a lot for commenting again, I think it is a pretty nice feature!