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Feat: Add ignore-areas #95

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ca686a2
feat: add ignore area
damblatt Jun 24, 2026
9a4c176
fix: no color diff overlay in ignored area
damblatt Jun 24, 2026
ea7a9f5
feat: allow multiple areas
damblatt Jun 24, 2026
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105 changes: 102 additions & 3 deletions diff-pdf.cpp
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Original file line number Diff line number Diff line change
Expand Up @@ -41,6 +41,7 @@
#include <wx/artprov.h>
#include <wx/progdlg.h>
#include <wx/filesys.h>
#include <wx/tokenzr.h>


enum DisplayMode
Expand All @@ -64,6 +65,11 @@ bool g_grayscale = false;
#define DEFAULT_RESOLUTION 300
long g_resolution = DEFAULT_RESOLUTION;

// Rectangles (in PDF points, origin top-left) within which differences are
// ignored entirely.
struct IgnoreArea { double x, y, w, h; };
std::vector<IgnoreArea> g_ignore_areas;

inline unsigned char to_grayscale(unsigned char r, unsigned char g, unsigned char b)
{
return (unsigned char)(0.2126 * r + 0.7152 * g + 0.0722 * b);
Expand Down Expand Up @@ -174,6 +180,35 @@ cairo_surface_t *diff_images(int page, cairo_surface_t *s1, cairo_surface_t *s2,
const unsigned char *data2 = s2 ? cairo_image_surface_get_data(s2) : NULL;
unsigned char *datadiff = cairo_image_surface_get_data(diff);

// convert the ignore areas from PDF points to pixel coordinates in the
// rdiff coordinate space:
std::vector<wxRect> ignore_px;
{
const double scale = (int)g_resolution / 72.0;
for ( size_t i = 0; i < g_ignore_areas.size(); i++ )
{
const IgnoreArea& a = g_ignore_areas[i];
// round the edges individually (rather than rounding width/height
// separately) so the rectangle covers every pixel that the
// rasterizer may have touched, including anti-aliased borders
const int px1 = wxRound(a.x * scale);
const int py1 = wxRound(a.y * scale);
const int px2 = wxRound((a.x + a.w) * scale);
const int py2 = wxRound((a.y + a.h) * scale);
ignore_px.push_back(wxRect(px1 + r1.x, py1 + r1.y, px2 - px1, py2 - py1));
}
}

auto is_ignored = [&ignore_px](int x, int y) -> bool
{
for ( size_t i = 0; i < ignore_px.size(); i++ )
{
if ( ignore_px[i].Contains(x, y) )
return true;
}
return false;
};

// we visualize the differences by taking one channel from s1
// and the other two channels from s2:

Expand Down Expand Up @@ -210,9 +245,13 @@ cairo_surface_t *diff_images(int page, cairo_surface_t *s1, cairo_surface_t *s2,
unsigned char cg2 = *(data2 + x + 1);
unsigned char cb2 = *(data2 + x + 2);

if ( cr1 > (cr2+g_channel_tolerance) || cr1 < (cr2-g_channel_tolerance)
|| cg1 > (cg2+g_channel_tolerance) || cg1 < (cg2-g_channel_tolerance)
|| cb1 > (cb2+g_channel_tolerance) || cb1 < (cb2-g_channel_tolerance)
const bool ignored = is_ignored(r2.x + x/4, r2.y + y);

if ( ( cr1 > (cr2+g_channel_tolerance) || cr1 < (cr2-g_channel_tolerance)
|| cg1 > (cg2+g_channel_tolerance) || cg1 < (cg2-g_channel_tolerance)
|| cb1 > (cb2+g_channel_tolerance) || cb1 < (cb2-g_channel_tolerance)
)
&& !ignored
)
{
pixel_diff_count++;
Expand All @@ -236,6 +275,13 @@ cairo_surface_t *diff_images(int page, cairo_surface_t *s1, cairo_surface_t *s2,
}
}

// leave pixels in the ignored area showing s1's original
// image, undistorted by the diff color overlay
if ( ignored )
{
continue;
}

if (g_grayscale)
{
// convert both images to grayscale, use blue for s1, red for s2
Expand Down Expand Up @@ -330,6 +376,23 @@ cairo_surface_t *diff_images(int page, cairo_surface_t *s1, cairo_surface_t *s2,
// If we specified a tolerance, then return if we have exceeded that for this page
if ( g_per_page_pixel_tolerance == 0 ? changes : pixel_diff_count > g_per_page_pixel_tolerance)
{
if ( !ignore_px.empty() )
{
// mark the ignored areas with a dashed gray outline, so it's
// clear when reviewing the diff that they were excluded on purpose
cairo_t *cr = cairo_create(diff);
static const double dashes[] = { 4.0, 4.0 };
cairo_set_dash(cr, dashes, 2, 0);
cairo_set_line_width(cr, 2.0);
cairo_set_source_rgb(cr, 0.5, 0.5, 0.5);
for ( size_t i = 0; i < ignore_px.size(); i++ )
{
cairo_rectangle(cr, ignore_px[i].x, ignore_px[i].y, ignore_px[i].width, ignore_px[i].height);
cairo_stroke(cr);
}
cairo_destroy(cr);
}

return diff;
}
else
Expand Down Expand Up @@ -991,6 +1054,12 @@ int main(int argc, char *argv[])
NULL, "per-page-pixel-tolerance", "total number of pixels allowed to be different per page before specifying the page is different",
wxCMD_LINE_VAL_NUMBER },

{ wxCMD_LINE_OPTION,
NULL, "ignore-area", "ignore differences inside one or more rectangles, each given as X,Y,WIDTH,HEIGHT in PDF points"
"(X,Y is the rectangle's top-left corner, measured from the page's top-left corner); separate multiple rectangles with ';',"
"e.g. --ignore-area=\"20,750,80,80;480,700,40,40\"",
wxCMD_LINE_VAL_STRING },

{ wxCMD_LINE_OPTION,
NULL, "dpi", "rasterization resolution (default: " wxSTRINGIZE(DEFAULT_RESOLUTION) " dpi)",
wxCMD_LINE_VAL_NUMBER },
Expand Down Expand Up @@ -1065,6 +1134,36 @@ int main(int argc, char *argv[])
}
}

wxString ignore_area_str;
if ( parser.Found("ignore-area", &ignore_area_str) )
{
wxStringTokenizer area_tokenizer(ignore_area_str, ";");
while ( area_tokenizer.HasMoreTokens() )
{
const wxString one_area = area_tokenizer.GetNextToken();

wxStringTokenizer tokenizer(one_area, ",");
double values[4];
bool ok = true;
size_t count = 0;
while ( ok && tokenizer.HasMoreTokens() && count < 4 )
ok = tokenizer.GetNextToken().ToCDouble(&values[count++]);
ok = ok && (count == 4) && !tokenizer.HasMoreTokens();

if ( !ok || values[2] <= 0 || values[3] <= 0 )
{
fprintf(stderr, "Invalid ignore-area: %s. Expected one or more X,Y,WIDTH,HEIGHT "
"rectangles (in PDF points; X,Y = top-left corner, measured from the "
"page's top-left corner; WIDTH,HEIGHT > 0), separated by ';', e.g. 20,750,80,80;480,700,40,40\n",
(const char*) ignore_area_str.c_str());
return 2;
}

IgnoreArea area = { values[0], values[1], values[2], values[3] };
g_ignore_areas.push_back(area);
}
}

if ( parser.Found("channel-tolerance", &g_channel_tolerance) )
{
if (g_channel_tolerance < 0 || g_channel_tolerance > 255) {
Expand Down