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Encode premultiplied alpha in render_ctx.rs

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This commit is contained in:
Tatsuyuki Ishi 2021-04-11 13:20:40 +09:00
parent f4be74c07f
commit 0637e2d6e5
2 changed files with 42 additions and 26 deletions
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10
piet-gpu/src/lib.rs
View file

@ -127,16 +127,12 @@ fn render_clip_test(rc: &mut impl RenderContext) {
#[allow(unused)]
fn render_alpha_test(rc: &mut impl RenderContext) {
// Alpha compositing tests. kernel4 expects colors encoded in alpha-premultiplied sRGB:
//
// [α,sRGB(α⋅R),sRGB(α⋅G),sRGB(α⋅B)]
//
// See also http://ssp.impulsetrain.com/gamma-premult.html.
// Alpha compositing tests.
rc.fill(diamond(Point::new(1024.0, 100.0)), &Color::Rgba32(0xff0000ff));
rc.fill(diamond(Point::new(1024.0, 125.0)), &Color::Rgba32(0x00ba0080));
rc.fill(diamond(Point::new(1024.0, 125.0)), &Color::Rgba32(0x00ff0080));
rc.save();
rc.clip(diamond(Point::new(1024.0, 150.0)));
rc.fill(diamond(Point::new(1024.0, 175.0)), &Color::Rgba32(0x0000ba80));
rc.fill(diamond(Point::new(1024.0, 175.0)), &Color::Rgba32(0x0000ff80));
rc.restore();
}

58
piet-gpu/src/render_ctx.rs
View file

@ -1,21 +1,19 @@
use std::{borrow::Cow, ops::RangeBounds};
use piet_gpu_types::encoder::{Encode, Encoder};
use piet_gpu_types::scene::{
Clip, CubicSeg, Element, FillColor, SetFillMode, LineSeg, QuadSeg, SetLineWidth, Transform,
};
use piet::{
kurbo::{Affine, Insets, PathEl, Point, Rect, Shape, Size},
HitTestPosition, TextAttribute, TextStorage,
HitTestPosition,
kurbo::{Affine, Insets, PathEl, Point, Rect, Shape, Size}, TextAttribute, TextStorage,
};
use piet::{
Color, Error, FixedGradient, FontFamily, HitTestPoint, ImageFormat, InterpolationMode,
IntoBrush, LineMetric, RenderContext, StrokeStyle, Text, TextLayout, TextLayoutBuilder,
};
use piet_gpu_types::encoder::{Encode, Encoder};
use piet_gpu_types::scene::{
Clip, CubicSeg, Element, FillColor, LineSeg, QuadSeg, SetFillMode, SetLineWidth, Transform,
};
pub struct PietGpuImage;
#[derive(Clone)]
@ -70,7 +68,7 @@ struct ClipElement {
bbox: Option<Rect>,
}
#[derive(Clone,Copy,PartialEq)]
#[derive(Clone, Copy, PartialEq)]
enum FillMode {
// Fill path according to the non-zero winding rule.
Nonzero = 0,
@ -138,7 +136,14 @@ impl RenderContext for PietGpuRenderContext {
}
fn solid_brush(&mut self, color: Color) -> Self::Brush {
PietGpuBrush::Solid(color.as_rgba_u32())
// kernel4 expects colors encoded in alpha-premultiplied sRGB:
//
// [α,sRGB(α⋅R),sRGB(α⋅G),sRGB(α⋅B)]
//
// See also http://ssp.impulsetrain.com/gamma-premult.html.
let (r, g, b, a) = color.as_rgba();
let premul = Color::rgba(to_srgb(from_srgb(r) * a), to_srgb(from_srgb(g) * a), to_srgb(from_srgb(b) * a), a);
PietGpuBrush::Solid(premul.as_rgba_u32())
}
fn gradient(&mut self, _gradient: impl Into<FixedGradient>) -> Result<Self::Brush, Error> {
@ -176,8 +181,7 @@ impl RenderContext for PietGpuRenderContext {
_brush: &impl IntoBrush<Self>,
_width: f64,
_style: &StrokeStyle,
) {
}
) {}
fn fill(&mut self, shape: impl Shape, brush: &impl IntoBrush<Self>) {
let brush = brush.make_brush(self, || shape.bounding_box()).into_owned();
@ -279,8 +283,7 @@ impl RenderContext for PietGpuRenderContext {
_image: &Self::Image,
_rect: impl Into<Rect>,
_interp: InterpolationMode,
) {
}
) {}
fn draw_image_area(
&mut self,
@ -288,8 +291,7 @@ impl RenderContext for PietGpuRenderContext {
_src_rect: impl Into<Rect>,
_dst_rect: impl Into<Rect>,
_interp: InterpolationMode,
) {
}
) {}
fn blurred_rect(&mut self, _rect: Rect, _blur_radius: f64, _brush: &impl IntoBrush<Self>) {}
@ -320,7 +322,7 @@ impl PietGpuRenderContext {
self.pathseg_count += 1;
}
fn encode_path(&mut self, path: impl Iterator<Item = PathEl>, is_fill: bool) {
fn encode_path(&mut self, path: impl Iterator<Item=PathEl>, is_fill: bool) {
if is_fill {
self.encode_path_inner(path.flat_map(|el| {
match el {
@ -335,7 +337,7 @@ impl PietGpuRenderContext {
}
}
fn encode_path_inner(&mut self, path: impl Iterator<Item = PathEl>) {
fn encode_path_inner(&mut self, path: impl Iterator<Item=PathEl>) {
let flatten = false;
if flatten {
let mut start_pt = None;
@ -583,3 +585,21 @@ fn to_scene_transform(transform: Affine) -> Transform {
translate: [c[4] as f32, c[5] as f32],
}
}
fn to_srgb(f: f64) -> f64 {
if f <= 0.0031308 {
f * 12.92
} else {
let a = 0.055;
(1. + a) * f64::powf(f, f64::recip(2.4)) - a
}
}
fn from_srgb(f: f64) -> f64 {
if f <= 0.04045 {
f / 12.92
} else {
let a = 0.055;
f64::powf((f + a) * f64::recip(1. + a), 2.4)
}
}