Metal alpha blending fixes + color handling improvements #4913
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Otherwise pages may have the wrong width if they were resized down with a fast path that just chanes the size without adjusting capacity at all.
This commit is quite large because it's fairly interconnected and can't be split up in a logical way. The main part of this commit is that alpha blending is now always done in the Display P3 color space, and depending on the configured `window-colorspace` colors will be converted from sRGB or assumed to already be Display P3 colors. In addition, a config option `text-blending` has been added which allows the user to configure linear blending (AKA "gamma correction"). Linear alpha blending also applies to images and makes custom shaders receive linear colors rather than sRGB. In addition, an experimental option has been added which corrects linear blending's tendency to make dark text look too thin and bright text look too thick. Essentially it's a correction curve on the alpha channel that depends on the luminance of the glyph being drawn.
| /// text rendered with non-linear blending. | ||
| /// | ||
| /// Has no effect if not using linear `text-blending`. | ||
| @"experimental-linear-correction": bool = false, |
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Not ready to review the whole thing but knee jerk reaction: should this be an alternate enum value for text-blending, i.e. linear-experimental?
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Probably. I set up the config options and then sorta just left them how I put them at first. It might also make sense to rename text-blending to alpha-blending. I'd also kinda like to rename window-colorspace to terminal-colorspace since what it does is define how terminal colors should be interpreted for rendering, but that felt out-of-scope for this PR.
| } else .{ | ||
| .color = true, | ||
| .depth = 4, | ||
| .space = try macos.graphics.ColorSpace.createDeviceRGB(), | ||
| .space = try macos.graphics.ColorSpace.createNamed(.displayP3), |
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@qwerasd205 suggestion: Should we make this ...ColorSpace.createFromName(.displayP3)?
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Why? I could understand changing it to createWithName if we wanted to match the name of the CoreGraphics function, but this really feels like splitting hairs either way. I'm not devoted to the name, but if I changed it I'd be more likely to change it to createWithName than createFromName unless there's particularly good reasoning...
This PR addresses #2125 for the Metal renderer. Both options are available: "Apple-style" blending where colors are blended in a wide gamut color space, which reduces but does not eliminate artifacts; and linear blending where colors are blended in linear RGB.
Because this doesn't add support for linear blending on Linux, I don't know whether the issue should be closed or not.
List of changes in no particular order
window-colorspacetodisplay-p3then terminal colors are automatically converted from sRGB to the corresponding Display P3 color in the shaderbackgroundColorproperty on theCAMetalLayer, because this should fix the flash of transparency during startup (macOS: background bleeds/flicker when resizing splits, creating tabs #4516) and the weirdness at the edge of the window when resizing. I didn't make that a part of this PR because it requires further changes and my changes are already pretty significant, but I can make it a follow-up.Main takeaways
Color blending now matches nearly identically to Apple apps like Terminal.app and TextEdit, not quite identical in worst case scenarios, off by the tiniest bit, because the default color space is slightly different than Display P3.
Linear alpha blending is now available for mac users who prefer more accurate color reproduction, and personally I think it looks very nice with the alpha correction turned on, I will be daily driving that configuration.
Future work
CALayer.backgroundColorinstead of in shader, to avoid issues around edges when resizing.