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webgl: Add support for premultiplying alpha.

Now the affected testcase only fails due to unpack alignment.
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anholt committed Jan 28, 2017
1 parent 57ba164 commit dfc4de0d8481c10b5ce1200a6a392acfe26c4143
@@ -417,6 +417,10 @@ pub fn byte_swap(data: &mut [u8]) {
}
}

pub fn multiply_u8_pixel(a: u8, b: u8) -> u8 {
return (a as u32 * b as u32 / 255) as u8;
}

pub fn byte_swap_and_premultiply(data: &mut [u8]) {
let length = data.len();

@@ -427,9 +431,9 @@ pub fn byte_swap_and_premultiply(data: &mut [u8]) {
let b = data[i + 0];
let a = data[i + 3];

data[i + 0] = ((r as u32) * (a as u32) / 255) as u8;
data[i + 1] = ((g as u32) * (a as u32) / 255) as u8;
data[i + 2] = ((b as u32) * (a as u32) / 255) as u8;
data[i + 0] = multiply_u8_pixel(r, a);
data[i + 1] = multiply_u8_pixel(g, a);
data[i + 2] = multiply_u8_pixel(b, a);

i += 4;
}
@@ -2,8 +2,8 @@
* 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/. */

use byteorder::{NativeEndian, WriteBytesExt};
use canvas_traits::{CanvasCommonMsg, CanvasMsg, byte_swap};
use byteorder::{NativeEndian, ReadBytesExt, WriteBytesExt};
use canvas_traits::{CanvasCommonMsg, CanvasMsg, byte_swap, multiply_u8_pixel};
use core::nonzero::NonZero;
use dom::bindings::codegen::Bindings::WebGLRenderingContextBinding::{self, WebGLContextAttributes};
use dom::bindings::codegen::Bindings::WebGLRenderingContextBinding::WebGLRenderingContextConstants as constants;
@@ -113,6 +113,7 @@ fn has_invalid_blend_constants(arg1: u32, arg2: u32) -> bool {
(_, _) => false
}
}

/// Set of bitflags for texture unpacking (texImage2d, etc...)
bitflags! {
#[derive(HeapSizeOf, JSTraceable)]
@@ -560,6 +561,72 @@ impl WebGLRenderingContext {
flipped
}

/// Performs premultiplication of the pixels if
/// UNPACK_PREMULTIPLY_ALPHA_WEBGL is currently enabled.
fn premultiply_pixels(&self,
format: TexFormat,
data_type: TexDataType,
pixels: Vec<u8>) -> Vec<u8> {
if !self.texture_unpacking_settings.get().contains(PREMULTIPLY_ALPHA) {
return pixels;
}

match (format, data_type) {
(TexFormat::RGBA, TexDataType::UnsignedByte) => {
let mut premul = Vec::<u8>::with_capacity(pixels.len());
for rgba in pixels.chunks(4) {
premul.push(multiply_u8_pixel(rgba[0], rgba[3]));
premul.push(multiply_u8_pixel(rgba[1], rgba[3]));
premul.push(multiply_u8_pixel(rgba[2], rgba[3]));
premul.push(rgba[3]);
}
premul
}
(TexFormat::LuminanceAlpha, TexDataType::UnsignedByte) => {
let mut premul = Vec::<u8>::with_capacity(pixels.len());
for la in pixels.chunks(2) {
premul.push(multiply_u8_pixel(la[0], la[1]));
premul.push(la[1]);
}
premul
}

(TexFormat::RGBA, TexDataType::UnsignedShort5551) => {
let mut premul = Vec::<u8>::with_capacity(pixels.len());
for mut rgba in pixels.chunks(2) {
let pix = rgba.read_u16::<NativeEndian>().unwrap();
if pix & (1 << 15) != 0 {
premul.write_u16::<NativeEndian>(pix).unwrap();
} else {
premul.write_u16::<NativeEndian>(0).unwrap();
}
}
premul
}

(TexFormat::RGBA, TexDataType::UnsignedShort4444) => {
let mut premul = Vec::<u8>::with_capacity(pixels.len());
for mut rgba in pixels.chunks(2) {
let pix = rgba.read_u16::<NativeEndian>().unwrap();
let extend_to_8_bits = |val| { (val | val << 4) as u8 };
let r = extend_to_8_bits(pix & 0x000f);
let g = extend_to_8_bits((pix & 0x00f0) >> 4);
let b = extend_to_8_bits((pix & 0x0f00) >> 8);
let a = extend_to_8_bits((pix & 0xf000) >> 12);

premul.write_u16::<NativeEndian>((multiply_u8_pixel(r, a) & 0xf0) as u16 >> 4 |
(multiply_u8_pixel(g, a) & 0xf0) as u16 |
((multiply_u8_pixel(b, a) & 0xf0) as u16) << 4 |
pix & 0xf000).unwrap();
}
premul
}

// Other formats don't have alpha, so return their data untouched.
_ => pixels
}
}

fn tex_image_2d(&self,
texture: Root<WebGLTexture>,
target: TexImageTarget,
@@ -570,11 +637,8 @@ impl WebGLRenderingContext {
height: u32,
_border: u32,
pixels: Vec<u8>) { // NB: pixels should NOT be premultipied
if internal_format == TexFormat::RGBA &&
data_type == TexDataType::UnsignedByte &&
self.texture_unpacking_settings.get().contains(PREMULTIPLY_ALPHA) {
// TODO(emilio): premultiply here.
}
// FINISHME: Consider doing premultiply and flip in a single mutable Vec.
let pixels = self.premultiply_pixels(internal_format, data_type, pixels);

let pixels = self.flip_teximage_y(pixels, internal_format, data_type,
width as usize, height as usize);
@@ -587,7 +651,7 @@ impl WebGLRenderingContext {
level,
Some(data_type)));

// TODO(emilio): convert colorspace, premultiply alpha if requested
// TODO(emilio): convert colorspace if requested
let msg = WebGLCommand::TexImage2D(target.as_gl_constant(), level as i32,
internal_format.as_gl_constant() as i32,
width as i32, height as i32,
@@ -632,10 +696,13 @@ impl WebGLRenderingContext {
return self.webgl_error(InvalidOperation);
}

// FINISHME: Consider doing premultiply and flip in a single mutable Vec.
let pixels = self.premultiply_pixels(format, data_type, pixels);

let pixels = self.flip_teximage_y(pixels, format, data_type,
width as usize, height as usize);

// TODO(emilio): convert colorspace, premultiply alpha if requested
// TODO(emilio): convert colorspace if requested
let msg = WebGLCommand::TexSubImage2D(target.as_gl_constant(),
level as i32, xoffset, yoffset,
width as i32, height as i32,

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