Use blend function from the image crate

examples/simple.rs

@@ -5,7 +5,7 @@
 //! and and then renders it into a PNG using the `image` crate.
 
 use image::codecs::png::PngEncoder;
-use image::{self, Rgba, RgbaImage};
+use image::{self, Pixel, Rgba, RgbaImage};
 use parley::layout::{Alignment, GlyphRun, Layout};
 use parley::style::{FontStack, FontWeight, StyleProperty};
 use parley::{FontContext, LayoutContext};
@@ -16,56 +16,6 @@ use swash::scale::{Render, ScaleContext, Source, StrikeWith};
 use swash::zeno;
 use swash::{FontRef, GlyphId};
 
-fn u8_to_float(num: u8) -> f32 {
-    num as f32 / 255.0
-}
-
-fn float_to_u8(num: f32) -> u8 {
-    (num * 255.0) as u8
-}
-
-fn to_linear_rgb(srgb: f32) -> f32 {
-    if srgb <= 0.04045 {
-        srgb / 12.92
-    } else {
-        ((srgb + 0.055) / 1.055).powf(2.4)
-    }
-}
-
-fn to_srgb(linear_rgb: f32) -> f32 {
-    if linear_rgb <= 0.0031308 {
-        linear_rgb * 12.92
-    } else {
-        1.055 * linear_rgb.powf(1.0 / 2.4) - 0.055
-    }
-}
-
-fn blend_px_gamma_corrected(existing: Rgba<u8>, color: Color, alpha: u8) -> Rgba<u8> {
-    let [r1, g1, b1, _] = existing.0.map(|x| to_linear_rgb(u8_to_float(x)));
-    let [r2, g2, b2] = [color.r, color.g, color.b].map(|x| to_linear_rgb(u8_to_float(x)));
-
-    let a = u8_to_float(alpha);
-    let inv_a = 1.0 - a;
-
-    // Blend pixel with underlying color
-    let r = a * r2 + inv_a * r1;
-    let g = a * g2 + inv_a * g1;
-    let b = a * b2 + inv_a * b1;
-
-    Rgba([r, g, b, 1.0].map(|x| float_to_u8(to_srgb(x))))
-}
-
-fn blend_px_naive(existing: Rgba<u8>, color: Color, alpha: u8) -> Rgba<u8> {
-    let inv_a = (255 - alpha) as u32;
-    let [r2, g2, b2, a2] = [color.r, color.g, color.b, alpha].map(u32::from);
-    let [r1, g1, b1, _a1] = existing.0.map(u32::from);
-    let r = (a2 * r2 + inv_a * r1) >> 8;
-    let g = (a2 * g2 + inv_a * g1) >> 8;
-    let b = (a2 * b2 + inv_a * b1) >> 8;
-
-    Rgba([r as u8, g as u8, b as u8, 255])
-}
-
 fn main() {
     // The text we are going to style and lay out
     let text = String::from(
@@ -202,8 +152,8 @@ fn render_glyph_run(
                         let y = (glyph_origin_y + off_y) as u32;
                         let alpha = rendered_glyph.data[i];
                         if alpha > 0 {
-                            let color = blend_px_naive(*img.get_pixel(x, y), color, alpha);
-                            img.put_pixel(x, y, color);
+                            let color = Rgba::from([color.r, color.g, color.b, alpha]);
+                            img.get_pixel_mut(x, y).blend(&color);
                         }
                         i += 1;
                     }
@@ -223,9 +173,8 @@ fn render_glyph_run(
                         let x = (glyph_origin_x + off_x as i32) as u32;
                         let y = (glyph_origin_y + off_y as i32) as u32;
                         if a > 0 {
-                            let color =
-                                blend_px_naive(*img.get_pixel(x, y), Color::rgb8(r, g, b), a);
-                            img.put_pixel(x, y, color);
+                            let color = Rgba::from([r, g, b, a]);
+                            img.get_pixel_mut(x, y).blend(&color);
                         }
                     }
                 }