Add background_image

[ctrlcctrlv]

This PR closes #163, and builds off my prior work in #2311 and 8020657, and also work by @kovidgoyal to correct my mistakes, which made this possible.

This PR has been tested both on Nvidia's proprietary OpenGL driver, and Mesa, both on Arch Linux. Sorry, I have no ability to test on OS X, (which is also an impediment to my work on FontForge, but my friends there test it for me,) but think it should work.

@kovidgoyal asked if I enjoyed the journey. I really did! Never did anything with OpenGL before this. It perhaps folly to take this on as my first OpenGL project, but hopefully users enjoy the result of much trial and error.

Scaled examples

Tiling examples

[ctrlcctrlv]

Sorry @kovidgoyal, I don't really understand how the Python test framework is supposed to work, it seems that by changing the available options I broke something, perhaps I failed to properly declare it in Python

[kovidgoyal]

Dont worry about it I will fix it when I merge.

[kovidgoyal]

FYI, I'll be reviewing (and probably merging) this over the next few days.

[ctrlcctrlv]

Thank you :-) I will in that case not make any more commits to the branch until your first review, to give you a stable base to review.

[kovidgoyal]

I have merged, with various fixes, please test to see that I have not broken anything. And if you have questions about my changes feel free to ask.

[kovidgoyal]

@Luflosi I'd appreciate if you could test that background iamges work on macOS since I dont currently have access to my mac.

[Luflosi]

Will do during the weekend.

[Luflosi]

Sorry for the delay but I finally tested it and it works mostly as expected:

Making this work with more image formats would be nice. What would be needed to make this work with JPEG images?
I noticed that part of the tab bar (in the not active tab) is transparent. I guess this is not intended and should probably be fixed. The right of the tab bar, where there are no tabs is currently filled with the background color. It may be desirable to show the background image there.
I also tested transparency and it works as expected.
When I tested with background_tint 0.95, I noticed one pixel wide strips on the right and bottom where the background_tint is not applied. I know that the tint is not applied to the margin/borders but I expected to have no margins since my window size is defined with cells:
initial_window_width 80c and initial_window_height 28c.

Here the same screenshot again with hide_window_decorations yes:

There must be an off-by-one error somewhere, either in the window size calculation or in the calculation for the tint. How can I help to debug this?

[ctrlcctrlv]

It might also be due to the blank rectangles Kitty draws for borders, in anticipation of having multiple visible Kitty windows in an OS window.

In re JPEG, it's not that much work to support, but would require a new dependency. That might not be a problem, libjpeg is extremely common, but I figured it better to keep the code simpler by choosing one image format which implements everything supported by Kitty (alpha).

[kovidgoyal]

On Sat, Feb 15, 2020 at 05:15:57PM -0800, Fredrick Brennan wrote: It might also be due to the blank rectangles Kitty draws for borders, in anticipation of having multiple visible Kitty windows in an OS window.

It almost certainly is the borders. @Luflosi you can check by comenting out various bits of code in borders.py

In re JPEG, it's not that much work to support, but would require a new dependency. That might not be a problem, libjpeg is extremely common, but I figured it better to keep the code simpler by choosing one image format which implements everything supported by Kitty (alpha).

I'd really rather not start depending on multiple libraries for multiple image formats. It's not that much of a hardship to ask users to convert images to PNG before using them as backgrounds.