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diff --git a/gfx/wr/webrender/src/gamma_lut.rs b/gfx/wr/webrender/src/gamma_lut.rs
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+++ b/gfx/wr/webrender/src/gamma_lut.rs
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+/* This Source Code Form is subject to the terms of the Mozilla Public
+ * License, v. 2.0. If a copy of the MPL was not distributed with this
+ * file, You can obtain one at http://mozilla.org/MPL/2.0/. */
+
+/*!
+Gamma correction lookup tables.
+
+This is a port of Skia gamma LUT logic into Rust, used by WebRender.
+*/
+//#![warn(missing_docs)] //TODO
+#![allow(dead_code)]
+
+use api::ColorU;
+use std::cmp::max;
+
+/// Color space responsible for converting between lumas and luminances.
+#[derive(Clone, Copy, Debug, PartialEq)]
+pub enum LuminanceColorSpace {
+    /// Linear space - no conversion involved.
+    Linear,
+    /// Simple gamma space - uses the `luminance ^ gamma` function.
+    Gamma(f32),
+    /// Srgb space.
+    Srgb,
+}
+
+impl LuminanceColorSpace {
+    pub fn new(gamma: f32) -> LuminanceColorSpace {
+        if gamma == 1.0 {
+            LuminanceColorSpace::Linear
+        } else if gamma == 0.0 {
+            LuminanceColorSpace::Srgb
+        } else {
+            LuminanceColorSpace::Gamma(gamma)
+        }
+    }
+
+    pub fn to_luma(&self, luminance: f32) -> f32 {
+        match *self {
+            LuminanceColorSpace::Linear => luminance,
+            LuminanceColorSpace::Gamma(gamma) => luminance.powf(gamma),
+            LuminanceColorSpace::Srgb => {
+                //The magic numbers are derived from the sRGB specification.
+                //See http://www.color.org/chardata/rgb/srgb.xalter .
+                if luminance <= 0.04045 {
+                    luminance / 12.92
+                } else {
+                    ((luminance + 0.055) / 1.055).powf(2.4)
+                }
+            }
+        }
+    }
+
+    pub fn from_luma(&self, luma: f32) -> f32 {
+        match *self {
+            LuminanceColorSpace::Linear => luma,
+            LuminanceColorSpace::Gamma(gamma) => luma.powf(1. / gamma),
+            LuminanceColorSpace::Srgb => {
+                //The magic numbers are derived from the sRGB specification.
+                //See http://www.color.org/chardata/rgb/srgb.xalter .
+                if luma <= 0.0031308 {
+                    luma * 12.92
+                } else {
+                    1.055 * luma.powf(1./2.4) - 0.055
+                }
+            }
+        }
+    }
+}
+
+//TODO: tests
+fn round_to_u8(x : f32) -> u8 {
+    let v = (x + 0.5).floor() as i32;
+    assert!(0 <= v && v < 0x100);
+    v as u8
+}
+
+//TODO: tests
+/*
+ * Scales base <= 2^N-1 to 2^8-1
+ * @param N [1, 8] the number of bits used by base.
+ * @param base the number to be scaled to [0, 255].
+ */
+fn scale255(n: u8, mut base: u8) -> u8 {
+    base <<= 8 - n;
+    let mut lum = base;
+    let mut i = n;
+
+    while i < 8 {
+        lum |= base >> i;
+        i += n;
+    }
+
+    lum
+}
+
+// Computes the luminance from the given r, g, and b in accordance with
+// SK_LUM_COEFF_X. For correct results, r, g, and b should be in linear space.
+fn compute_luminance(r: u8, g: u8, b: u8) -> u8 {
+    // The following is
+    // r * SK_LUM_COEFF_R + g * SK_LUM_COEFF_G + b * SK_LUM_COEFF_B
+    // with SK_LUM_COEFF_X in 1.8 fixed point (rounding adjusted to sum to 256).
+    let val: u32 = r as u32 * 54 + g as u32 * 183 + b as u32 * 19;
+    assert!(val < 0x10000);
+    (val >> 8) as u8
+}
+
+// Skia uses 3 bits per channel for luminance.
+const LUM_BITS: u8 = 3;
+// Mask of the highest used bits.
+const LUM_MASK: u8 = ((1 << LUM_BITS) - 1) << (8 - LUM_BITS);
+
+pub trait ColorLut {
+    fn quantize(&self) -> ColorU;
+    fn quantized_floor(&self) -> ColorU;
+    fn quantized_ceil(&self) -> ColorU;
+    fn luminance(&self) -> u8;
+    fn luminance_color(&self) -> ColorU;
+}
+
+impl ColorLut for ColorU {
+    // Compute a canonical color that is equivalent to the input color
+    // for preblend table lookups. The alpha channel is never used for
+    // preblending, so overwrite it with opaque.
+    fn quantize(&self) -> ColorU {
+        ColorU::new(
+            scale255(LUM_BITS, self.r >> (8 - LUM_BITS)),
+            scale255(LUM_BITS, self.g >> (8 - LUM_BITS)),
+            scale255(LUM_BITS, self.b >> (8 - LUM_BITS)),
+            255,
+        )
+    }
+
+    // Quantize to the smallest value that yields the same table index.
+    fn quantized_floor(&self) -> ColorU {
+        ColorU::new(
+            self.r & LUM_MASK,
+            self.g & LUM_MASK,
+            self.b & LUM_MASK,
+            255,
+        )
+    }
+
+    // Quantize to the largest value that yields the same table index.
+    fn quantized_ceil(&self) -> ColorU {
+        ColorU::new(
+            self.r | !LUM_MASK,
+            self.g | !LUM_MASK,
+            self.b | !LUM_MASK,
+            255,
+        )
+    }
+
+    // Compute a luminance value suitable for grayscale preblend table
+    // lookups.
+    fn luminance(&self) -> u8 {
+        compute_luminance(self.r, self.g, self.b)
+    }
+
+    // Make a grayscale color from the computed luminance.
+    fn luminance_color(&self) -> ColorU {
+        let lum = self.luminance();
+        ColorU::new(lum, lum, lum, self.a)
+    }
+}
+
+// This will invert the gamma applied by CoreGraphics,
+// so we can get linear values.
+// CoreGraphics obscurely defaults to 2.0 as the smoothing gamma value.
+// The color space used does not appear to affect this choice.
+#[cfg(target_os="macos")]
+fn get_inverse_gamma_table_coregraphics_smoothing() -> [u8; 256] {
+    let mut table = [0u8; 256];
+
+    for (i, v) in table.iter_mut().enumerate() {
+        let x = i as f32 / 255.0;
+        *v = round_to_u8(x * x * 255.0);
+    }
+
+    table
+}
+
+// A value of 0.5 for SK_GAMMA_CONTRAST appears to be a good compromise.
+// With lower values small text appears washed out (though correctly so).
+// With higher values lcd fringing is worse and the smoothing effect of
+// partial coverage is diminished.
+fn apply_contrast(srca: f32, contrast: f32) -> f32 {
+    srca + ((1.0 - srca) * contrast * srca)
+}
+
+// The approach here is not necessarily the one with the lowest error
+// See https://bel.fi/alankila/lcd/alpcor.html for a similar kind of thing
+// that just search for the adjusted alpha value
+pub fn build_gamma_correcting_lut(table: &mut [u8; 256], src: u8, contrast: f32,
+                                  src_space: LuminanceColorSpace,
+                                  dst_convert: LuminanceColorSpace) {
+
+    let src = src as f32 / 255.0;
+    let lin_src = src_space.to_luma(src);
+    // Guess at the dst. The perceptual inverse provides smaller visual
+    // discontinuities when slight changes to desaturated colors cause a channel
+    // to map to a different correcting lut with neighboring srcI.
+    // See https://code.google.com/p/chromium/issues/detail?id=141425#c59 .
+    let dst = 1.0 - src;
+    let lin_dst = dst_convert.to_luma(dst);
+
+    // Contrast value tapers off to 0 as the src luminance becomes white
+    let adjusted_contrast = contrast * lin_dst;
+
+    // Remove discontinuity and instability when src is close to dst.
+    // The value 1/256 is arbitrary and appears to contain the instability.
+    if (src - dst).abs() < (1.0 / 256.0) {
+        let mut ii : f32 = 0.0;
+        for v in table.iter_mut() {
+            let raw_srca = ii / 255.0;
+            let srca = apply_contrast(raw_srca, adjusted_contrast);
+
+            *v = round_to_u8(255.0 * srca);
+            ii += 1.0;
+        }
+    } else {
+        // Avoid slow int to float conversion.
+        let mut ii : f32 = 0.0;
+        for v in table.iter_mut() {
+            // 'raw_srca += 1.0f / 255.0f' and even
+            // 'raw_srca = i * (1.0f / 255.0f)' can add up to more than 1.0f.
+            // When this happens the table[255] == 0x0 instead of 0xff.
+            // See http://code.google.com/p/chromium/issues/detail?id=146466
+            let raw_srca = ii / 255.0;
+            let srca = apply_contrast(raw_srca, adjusted_contrast);
+            assert!(srca <= 1.0);
+            let dsta = 1.0 - srca;
+
+            // Calculate the output we want.
+            let lin_out = lin_src * srca + dsta * lin_dst;
+            assert!(lin_out <= 1.0);
+            let out = dst_convert.from_luma(lin_out);
+
+            // Undo what the blit blend will do.
+            // i.e. given the formula for OVER: out = src * result + (1 - result) * dst
+            // solving for result gives:
+            let result = (out - dst) / (src - dst);
+
+            *v = round_to_u8(255.0 * result);
+            debug!("Setting {:?} to {:?}", ii as u8, *v);
+
+            ii += 1.0;
+        }
+    }
+}
+
+pub struct GammaLut {
+    tables: [[u8; 256]; 1 << LUM_BITS],
+    #[cfg(target_os="macos")]
+    cg_inverse_gamma: [u8; 256],
+}
+
+impl GammaLut {
+    // Skia actually makes 9 gamma tables, then based on the luminance color,
+    // fetches the RGB gamma table for that color.
+    fn generate_tables(&mut self, contrast: f32, paint_gamma: f32, device_gamma: f32) {
+        let paint_color_space = LuminanceColorSpace::new(paint_gamma);
+        let device_color_space = LuminanceColorSpace::new(device_gamma);
+
+        for (i, entry) in self.tables.iter_mut().enumerate() {
+            let luminance = scale255(LUM_BITS, i as u8);
+            build_gamma_correcting_lut(entry,
+                                       luminance,
+                                       contrast,
+                                       paint_color_space,
+                                       device_color_space);
+        }
+    }
+
+    pub fn table_count(&self) -> usize {
+        self.tables.len()
+    }
+
+    pub fn get_table(&self, color: u8) -> &[u8; 256] {
+        &self.tables[(color >> (8 - LUM_BITS)) as usize]
+    }
+
+    pub fn new(contrast: f32, paint_gamma: f32, device_gamma: f32) -> GammaLut {
+        #[cfg(target_os="macos")]
+        let mut table = GammaLut {
+            tables: [[0; 256]; 1 << LUM_BITS],
+            cg_inverse_gamma: get_inverse_gamma_table_coregraphics_smoothing(),
+        };
+        #[cfg(not(target_os="macos"))]
+        let mut table = GammaLut {
+            tables: [[0; 256]; 1 << LUM_BITS],
+        };
+
+        table.generate_tables(contrast, paint_gamma, device_gamma);
+
+        table
+    }
+
+    // Assumes pixels are in BGRA format. Assumes pixel values are in linear space already.
+    pub fn preblend(&self, pixels: &mut [u8], color: ColorU) {
+        let table_r = self.get_table(color.r);
+        let table_g = self.get_table(color.g);
+        let table_b = self.get_table(color.b);
+
+        for pixel in pixels.chunks_mut(4) {
+            let (b, g, r) = (table_b[pixel[0] as usize], table_g[pixel[1] as usize], table_r[pixel[2] as usize]);
+            pixel[0] = b;
+            pixel[1] = g;
+            pixel[2] = r;
+            pixel[3] = max(max(b, g), r);
+        }
+    }
+
+    // Assumes pixels are in BGRA format. Assumes pixel values are in linear space already.
+    pub fn preblend_scaled(&self, pixels: &mut [u8], color: ColorU, percent: u8) {
+        if percent >= 100 {
+            self.preblend(pixels, color);
+            return;
+        }
+
+        let table_r = self.get_table(color.r);
+        let table_g = self.get_table(color.g);
+        let table_b = self.get_table(color.b);
+        let scale = (percent as i32 * 256) / 100;
+
+        for pixel in pixels.chunks_mut(4) {
+            let (mut b, g, mut r) = (
+                table_b[pixel[0] as usize] as i32,
+                table_g[pixel[1] as usize] as i32,
+                table_r[pixel[2] as usize] as i32,
+            );
+            b = g + (((b - g) * scale) >> 8);
+            r = g + (((r - g) * scale) >> 8);
+            pixel[0] = b as u8;
+            pixel[1] = g as u8;
+            pixel[2] = r as u8;
+            pixel[3] = max(max(b, g), r) as u8;
+        }
+    }
+
+    #[cfg(target_os="macos")]
+    pub fn coregraphics_convert_to_linear(&self, pixels: &mut [u8]) {
+        for pixel in pixels.chunks_mut(4) {
+            pixel[0] = self.cg_inverse_gamma[pixel[0] as usize];
+            pixel[1] = self.cg_inverse_gamma[pixel[1] as usize];
+            pixel[2] = self.cg_inverse_gamma[pixel[2] as usize];
+        }
+    }
+
+    // Assumes pixels are in BGRA format. Assumes pixel values are in linear space already.
+    pub fn preblend_grayscale(&self, pixels: &mut [u8], color: ColorU) {
+        let table_g = self.get_table(color.g);
+
+        for pixel in pixels.chunks_mut(4) {
+            let luminance = compute_luminance(pixel[2], pixel[1], pixel[0]);
+            let alpha = table_g[luminance as usize];
+            pixel[0] = alpha;
+            pixel[1] = alpha;
+            pixel[2] = alpha;
+            pixel[3] = alpha;
+        }
+    }
+
+} // end impl GammaLut
+
+#[cfg(test)]
+mod tests {
+    use super::*;
+
+    fn over(dst: u32, src: u32, alpha: u32) -> u32 {
+        (src * alpha + dst * (255 - alpha))/255
+    }
+
+    fn overf(dst: f32, src: f32, alpha: f32) -> f32 {
+        ((src * alpha + dst * (255. - alpha))/255.) as f32
+    }
+
+
+    fn absdiff(a: u32, b: u32) -> u32 {
+        if a < b  { b - a } else { a - b }
+    }
+
+    #[test]
+    fn gamma() {
+        let mut table = [0u8; 256];
+        let g = 2.0;
+        let space = LuminanceColorSpace::Gamma(g);
+        let mut src : u32 = 131;
+        while src < 256 {
+            build_gamma_correcting_lut(&mut table, src as u8, 0., space, space);
+            let mut max_diff = 0;
+            let mut dst = 0;
+            while dst < 256 {
+                for alpha in 0u32..256 {
+                    let preblend = table[alpha as usize];
+                    let lin_dst = (dst as f32 / 255.).powf(g) * 255.;
+                    let lin_src = (src as f32 / 255.).powf(g) * 255.;
+
+                    let preblend_result = over(dst, src, preblend as u32);
+                    let true_result = ((overf(lin_dst, lin_src, alpha as f32) / 255.).powf(1. / g) * 255.) as u32;
+                    let diff = absdiff(preblend_result, true_result);
+                    //println!("{} -- {} {} = {}", alpha, preblend_result, true_result, diff);
+                    max_diff = max(max_diff, diff);
+                }
+
+                //println!("{} {} max {}", src, dst, max_diff);
+                assert!(max_diff <= 33);
+                dst += 1;
+
+            }
+            src += 1;
+        }
+    }
+} // end mod