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wezterm: more adventures with background alpha

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Is it *right*? Hard to say, but it looks better than
the behavior I see with master at the moment.

This is a partial revert of #413, but respins it to
try to get a better alpha value for glyphs.

refs: #413
refs: #470
This commit is contained in:
Wez Furlong 2021-02-13 13:16:37 -08:00
parent f697de82fc
commit 0473e1de78
2 changed files with 42 additions and 30 deletions
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2
wezterm-gui/src/gui/fragment.glsl
View File

@ -119,6 +119,8 @@ void main() {
// instead; this avoids generating shadowy anti-aliasing artifacts
// for something that should otherwise be invisible.
color = vec4(0.0, 0.0, 0.0, 0.0);
discard;
return;
} else {
color = multiply(o_fg_color, color);
}

70
wezterm-gui/src/gui/termwindow.rs
View File

@ -2745,9 +2745,8 @@ impl TermWindow {
)
.to_arrays_transposed();
let draw_params = glium::DrawParameters {
// No alpha blending for the background layer: let's make
// sure that our background pixels are at 100% opacity.
let alpha_blending = glium::DrawParameters {
blend: glium::Blend::alpha_blending(),
..Default::default()
};
@ -2779,31 +2778,9 @@ impl TermWindow {
bg_and_line_layer: false,
has_background_image: has_background_image,
},
&draw_params,
&alpha_blending,
)?;
let draw_params = glium::DrawParameters {
blend: glium::Blend {
color: BlendingFunction::Addition {
source: LinearBlendingFactor::SourceAlpha,
destination: LinearBlendingFactor::OneMinusSourceAlpha,
},
alpha: BlendingFunction::Addition {
source: LinearBlendingFactor::SourceAlpha,
// On Wayland, the compositor takes the destination alpha
// value and blends with the window behind our own, which
// can make the text look brighter or less sharp.
// We set the destination alpha to 1.0 to prevent that
// from happening.
// (The normal alpha blending operation would set this to
// OneMinusSourceAlpha).
destination: LinearBlendingFactor::One,
},
constant_value: (0.0, 0.0, 0.0, 0.0),
},
..Default::default()
};
// Pass 2: strikethrough and underline
frame.draw(
&*vb,
@ -2817,13 +2794,46 @@ impl TermWindow {
bg_and_line_layer: true,
has_background_image: has_background_image,
},
&draw_params,
&alpha_blending,
)?;
// Use regular alpha blending when we draw the glyphs!
// This is trying to avoid an issue that is most prevalent
// on Wayland and X11. If our glyph pixels end up with alpha
// that isn't 1.0 then the window behind can cause the resultant
// text to appear brighter or more bold, especially with a
// 100% white window behind.
//
// To avoid this, for the computed alpha channel, instruct
// the render phase to pick a larger alpha value.
// There doesn't appear to be a way to tell it to set the
// result to constant=1.0, only to influence the factors
// in the equation:
//
// alpha = src_alpha * src_factor + dest_alpha * dest_factor.
//
// src_alpha comes from the glyph we are rendering.
// dest_alpha comes from the background it is rendering over.
// src_factor from alpha.source below
// dest_factor from alpha.destination below
//
// If you're here troubleshooting this, please see:
// <https://github.com/wez/wezterm/issues/413>
let draw_params = glium::DrawParameters {
blend: glium::Blend::alpha_blending(),
// <https://github.com/wez/wezterm/issues/470>
let blend_but_set_alpha_to_one = glium::DrawParameters {
blend: glium::Blend {
// Standard alpha-blending color
color: BlendingFunction::Addition {
source: LinearBlendingFactor::SourceAlpha,
destination: LinearBlendingFactor::OneMinusSourceAlpha,
},
// Try to result in an alpha closer to 1.0
alpha: BlendingFunction::Addition {
source: LinearBlendingFactor::One,
destination: LinearBlendingFactor::One,
},
constant_value: (0.0, 0.0, 0.0, 0.0),
},
..Default::default()
};
@ -2840,7 +2850,7 @@ impl TermWindow {
bg_and_line_layer: false,
has_background_image: has_background_image,
},
&draw_params,
&blend_but_set_alpha_to_one,
)?;
Ok(())