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Simdify compareDifferentLayouts #148

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651a15f
Simdify compareDifferentLayouts
serpent7776 Oct 25, 2025
3ccd509
Use std.simd.iota
serpent7776 Oct 27, 2025
66d470a
Add more tests for different layout diffs
serpent7776 Nov 4, 2025
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209 changes: 143 additions & 66 deletions src/diff.zig
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Original file line number Diff line number Diff line change
Expand Up @@ -229,9 +229,6 @@ inline fn increment_coords_by(x: *u32, y: *u32, step: u32, width: u32) void {
}

pub noinline fn compareSameLayouts(base: *const Image, comp: *const Image, diff_output: *?Image, diff_count: *u32, diff_lines: ?*DiffLines, ignore_regions: ?[]struct { u32, u32 }, max_delta: i64, options: DiffOptions) !void {
var x: u32 = 0;
var y: u32 = 0;

const size = (base.height * base.width);
const base_data = base.data;
const comp_data = comp.data;
Expand All @@ -240,42 +237,52 @@ pub noinline fn compareSameLayouts(base: *const Image, comp: *const Image, diff_
const simd_end = (size / SIMD_SIZE) * SIMD_SIZE;

var offset: usize = 0;
const Vec = @Vector(SIMD_SIZE, u32);
var xs: Vec = std.simd.iota(u32, SIMD_SIZE);
var ys: Vec = @as(Vec, @splat(0));
while (offset < simd_end) : (offset += SIMD_SIZE) {
const base_vec: @Vector(SIMD_SIZE, u32) = base_data[offset .. offset + SIMD_SIZE][0..SIMD_SIZE].*;
const comp_vec: @Vector(SIMD_SIZE, u32) = comp_data[offset .. offset + SIMD_SIZE][0..SIMD_SIZE].*;
const base_vec: Vec = base_data[offset .. offset + SIMD_SIZE][0..SIMD_SIZE].*;
const comp_vec: Vec = comp_data[offset .. offset + SIMD_SIZE][0..SIMD_SIZE].*;

const diff_mask = base_vec != comp_vec;
if (!@reduce(.Or, diff_mask)) {
increment_coords_by(&x, &y, SIMD_SIZE, base.width);
continue;
}

for (0..SIMD_SIZE) |i| {
if (diff_mask[i]) {
const pixel_offset = offset + i;
const base_color = base_vec[i];
const comp_color = comp_vec[i];

try processPixelDifference(
pixel_offset,
base_color,
comp_color,
x,
y,
base,
comp,
diff_output,
diff_count,
diff_lines,
ignore_regions,
max_delta,
options,
);
if (@reduce(.Or, diff_mask)) {
for (0..SIMD_SIZE) |i| {
if (diff_mask[i]) {
const pixel_offset = offset + i;
const base_color = base_vec[i];
const comp_color = comp_vec[i];

try processPixelDifference(
pixel_offset,
base_color,
comp_color,
xs[i],
ys[i],
base,
comp,
diff_output,
diff_count,
diff_lines,
ignore_regions,
max_delta,
options,
);
}
}
increment_coords(&x, &y, base.width);
}

xs += @splat(SIMD_SIZE);
const width_vec: Vec = @splat(base.width);
const mask: @Vector(SIMD_SIZE, bool) = xs >= width_vec;
const inc_y: Vec = @select(u32, mask, @as(Vec, @splat(1)), @as(Vec, @splat(0)));
ys += inc_y;
xs -= @select(u32, mask, width_vec, @as(Vec, @splat(0)));
}

const width_usize: usize = base.width;
var x: u32 = @intCast(simd_end % width_usize);
var y: u32 = @intCast(simd_end / width_usize);

// Handle remaining pixels
while (offset < size) : (offset += 1) {
const base_color = base_data[offset];
Expand All @@ -302,47 +309,117 @@ pub noinline fn compareSameLayouts(base: *const Image, comp: *const Image, diff_
}
}

pub fn compareDifferentLayouts(base: *const Image, comp: *const Image, maybe_diff_output: *?Image, diff_count: *u32, diff_lines: ?*DiffLines, ignore_regions: ?[]struct { u32, u32 }, max_delta: i64, options: DiffOptions) !void {
var x: u32 = 0;
var y: u32 = 0;
var offset: u32 = 0;

const size = (base.height * base.width);
while (offset < size) : (offset += 1) {
const base_color = base.readRawPixel(x, y);
pub fn compareDifferentLayouts(base: *const Image, comp: *const Image, diff_output: *?Image, diff_count: *u32, diff_lines: ?*DiffLines, ignore_regions: ?[]struct { u32, u32 }, max_delta: i64, options: DiffOptions) !void {
const base_size = (base.height * base.width);
const base_data = base.data;
const comp_data = comp.data;

if (x >= comp.width or y >= comp.height) {
const alpha = (base_color >> 24) & 0xFF;
if (alpha != 0) {
diff_count.* += 1;
if (maybe_diff_output.*) |*output| {
output.setImgColor(x, y, options.diff_pixel);
const SIMD_SIZE = std.simd.suggestVectorLength(u32) orelse if (HAS_AVX512f) 16 else if (HAS_NEON) 8 else 4;
const min_width: u32 = @min(base.width, comp.width);
const min_height = @min(base.height, comp.height);
const steps: u32 = @intCast(min_width / SIMD_SIZE);
const base_delta: u32 = base.width - steps * SIMD_SIZE;
const comp_delta: u32 = comp.width - steps * SIMD_SIZE;

var base_offset: usize = 0;
var comp_offset: usize = 0;
const Vec = @Vector(SIMD_SIZE, u32);
var xs: Vec = std.simd.iota(u32, SIMD_SIZE);
var y: u32 = 0;
for (0..min_height) |_| {
for (0..steps) |_| {
const base_vec: Vec = base_data[base_offset .. base_offset + SIMD_SIZE][0..SIMD_SIZE].*;
const comp_vec: Vec = comp_data[comp_offset .. comp_offset + SIMD_SIZE][0..SIMD_SIZE].*;

const diff_mask = base_vec != comp_vec;
if (@reduce(.Or, diff_mask)) {
for (0..SIMD_SIZE) |i| {
if (diff_mask[i]) {
const pixel_offset = base_offset + i;
const base_color = base_vec[i];
const comp_color = comp_vec[i];

try processPixelDifference(
pixel_offset,
base_color,
comp_color,
xs[i],
y,
base,
comp,
diff_output,
diff_count,
diff_lines,
ignore_regions,
max_delta,
options,
);
}
}
}

if (diff_lines) |lines| {
lines.addLine(y);
xs += @as(Vec, @splat(SIMD_SIZE));
base_offset += SIMD_SIZE;
comp_offset += SIMD_SIZE;
}
// handle leftover pixels in a row
const processed: u32 = steps * SIMD_SIZE;
const remaining: u32 = base.width - processed;
for (0..remaining) |i| {
const x: u32 = processed + @as(u32, @intCast(i));
const base_color = base_data[base_offset + i];
if (x >= comp.width) {
const alpha = (base_color >> 24) & 0xFF;
if (alpha != 0) {
diff_count.* += 1;
if (diff_output.*) |*output| {
output.setImgColor(x, y, options.diff_pixel);
}

if (diff_lines) |lines| {
lines.addLine(y);
}
}
} else {
const comp_color = comp.readRawPixel(x, y);
try processPixelDifference(
base_offset + i,
base_color,
comp_color,
x,
y,
base,
comp,
diff_output,
diff_count,
diff_lines,
ignore_regions,
max_delta,
options,
);
}
} else {
const comp_color = comp.readRawPixel(x, y);

try processPixelDifference(
offset,
base_color,
comp_color,
x,
y,
base,
comp,
maybe_diff_output,
diff_count,
diff_lines,
ignore_regions,
max_delta,
options,
);
}
xs = std.simd.iota(u32, SIMD_SIZE);
y += 1;
base_offset += base_delta;
comp_offset += comp_delta;
}

// Handle remaining pixels
var x: u32 = 0;
while (base_offset < base_size) : (base_offset += 1) {
const base_color = base_data[base_offset];
const alpha = (base_color >> 24) & 0xFF;
if (alpha != 0) {
diff_count.* += 1;
if (diff_output.*) |*output| {
output.setImgColor(x, y, options.diff_pixel);
}

if (diff_lines) |lines| {
lines.addLine(y);
}
}
increment_coords(&x, &y, base.width);
}
}
Expand Down
51 changes: 46 additions & 5 deletions src/test_core.zig
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Original file line number Diff line number Diff line change
Expand Up @@ -201,10 +201,51 @@ test "layoutDifference: diff images with different layouts" {
.output_diff_mask = false,
};

var diff_output, const diff_count, const diff_percentage, var diff_lines = try diff.compare(&img1, &img2, options, allocator);
defer if (diff_output) |*img| img.deinit(allocator);
defer if (diff_lines) |*lines| lines.deinit();
{
var diff_output, const diff_count, const diff_percentage, var diff_lines = try diff.compare(&img1, &img2, options, allocator);
defer if (diff_output) |*img| img.deinit(allocator);
defer if (diff_lines) |*lines| lines.deinit();

try expectEqual(@as(u32, 16), diff_count); // diffPixels
try expectApproxEqRel(@as(f64, 100.0), diff_percentage, 0.001); // diffPercentage
try expectEqual(@as(u32, 16), diff_count); // diffPixels
try expectApproxEqRel(@as(f64, 100.0), diff_percentage, 0.001); // diffPercentage
}
{
var diff_output, const diff_count, const diff_percentage, var diff_lines = try diff.compare(&img2, &img1, options, allocator);
defer if (diff_output) |*img| img.deinit(allocator);
defer if (diff_lines) |*lines| lines.deinit();

try expectEqual(@as(u32, 64), diff_count); // diffPixels
try expectApproxEqRel(@as(f64, 100.0), diff_percentage, 0.001); // diffPercentage
}
}

test "layoutDifference: diff images with different layouts (2)" {
var gpa = std.heap.GeneralPurposeAllocator(.{}){};
defer _ = gpa.deinit();
const allocator = gpa.allocator();

var img1 = try loadTestImage("test/png/odiff-logo-dark.png", allocator);
defer img1.deinit(allocator);

var img2 = try loadTestImage("test/png/odiff-logo-dark-rotated.png", allocator);
defer img2.deinit(allocator);

const options = diff.DiffOptions{};

{
var diff_output, const diff_count, const diff_percentage, var diff_lines = try diff.compare(&img1, &img2, options, allocator);
defer if (diff_output) |*img| img.deinit(allocator);
defer if (diff_lines) |*lines| lines.deinit();

try expectEqual(@as(u32, 1209283), diff_count); // diffPixels
try expectApproxEqRel(@as(f64, 70.368), diff_percentage, 0.001); // diffPercentage
}
{
var diff_output, const diff_count, const diff_percentage, var diff_lines = try diff.compare(&img2, &img1, options, allocator);
defer if (diff_output) |*img| img.deinit(allocator);
defer if (diff_lines) |*lines| lines.deinit();

try expectEqual(@as(u32, 1209283), diff_count); // diffPixels
try expectApproxEqRel(@as(f64, 70.368), diff_percentage, 0.001); // diffPercentage
}
}
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