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use bytes;
use io;
use memio;
// Filter modes supported by PNG files.
export type filter = enum u8 {
NONE = 0,
SUB = 1,
UP = 2,
AVERAGE = 3,
PAETH = 4,
};
fn applyfilter(dec: *decoder) void = {
const mode = dec.filter as filter;
const bpp = dec.bpp;
switch (mode) {
case filter::NONE =>
yield; // no-op
case filter::SUB =>
for (let i = bpp; i < len(dec.cr); i += 1) {
dec.cr[i] += dec.cr[i - bpp];
};
case filter::UP =>
for (let i = 0z; i < len(dec.cr); i += 1) {
dec.cr[i] += dec.pr[i];
};
case filter::AVERAGE =>
for (let i = 0z; i < bpp; i += 1) {
dec.cr[i] += dec.pr[i] / 2;
};
for (let i = bpp; i < len(dec.cr); i += 1) {
dec.cr[i] += ((dec.cr[i - bpp]: int + dec.pr[i]: int) / 2): u8;
};
case filter::PAETH =>
applypaeth(dec);
};
dec.filter = void;
dec.pr[..] = dec.cr[..];
};
@test fn filter_none() void = {
const src = memio::fixed(no_filtering);
const image = load(&src)!;
defer image_finish(&image);
assert(bytes::equal(image.pixels, no_filtering_data));
};
@test fn filter_sub() void = {
const src = memio::fixed(filter_sub_png);
const image = load(&src)!;
defer image_finish(&image);
assert(bytes::equal(image.pixels, filter_sub_data));
};
@test fn filter_up() void = {
const src = memio::fixed(filter_up_png);
const image = load(&src)!;
defer image_finish(&image);
assert(bytes::equal(image.pixels, filter_up_data));
};
@test fn filter_average() void = {
const src = memio::fixed(filter_avg_png);
const image = load(&src)!;
defer image_finish(&image);
assert(bytes::equal(image.pixels, filter_avg_data));
};
@test fn filter_peath() void = {
const src = memio::fixed(filter_peath_png);
const image = load(&src)!;
defer image_finish(&image);
assert(bytes::equal(image.pixels, filter_peath_data));
};
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