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Fixed inaccurate image placement and even more resampling bugs #31021

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Merged
QuLogic merged 9 commits into from
Mar 2, 2026
Merged

Fixed inaccurate image placement and even more resampling bugs #31021

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89bbd1c
Fix making an image that is to be placed at a fractional pixel
ayshih Jan 22, 2026
0ecf660
Fix affine resampling when using nearest-neighbor interpolation
ayshih Jan 29, 2026
d9d7d15
Fix the handling of image resampling beyond the image bounds
ayshih Jan 29, 2026
2d37c64
Fix pixel alignment for PcolorImage and NonUniformImage
ayshih Jan 30, 2026
dd24e05
Switch to premultiplied space inside Agg for RGBA blending
ayshih Feb 3, 2026
35ccd4c
Adjust to favor the left input pixel for nearest-neighbor interpolation
ayshih Feb 4, 2026
f1a1fb4
Bump rendering edges to fill axes when rendering affine non-NN interp…
ayshih Feb 6, 2026
ae239ea
Add four figure tests and changelog entry
ayshih Jan 28, 2026
800185c
Adjust existing figure test and update baseline images
ayshih Feb 3, 2026
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Fix the handling of image resampling beyond the image bounds 
For nearest-neighbor interpolation, the code no longer applies any
antialiasing of edges under an affine transform for more accurate edges
and no longer shows data beyond the image bounds under a non-affine
transform.
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@ayshih
ayshih committed Mar 2, 2026
commit d9d7d15407859a877757d1dcb01e977b4dc3d58a
24 changes: 13 additions & 11 deletions src/_image_resample.h
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Original file line number Diff line number Diff line change
Expand Up @@ -708,7 +708,8 @@ void resample(
using scanline_t = agg::scanline32_u8;

using reflect_t = agg::wrap_mode_reflect;
using image_accessor_t = agg::image_accessor_wrap<input_pixfmt_t, reflect_t, reflect_t>;
using image_accessor_wrap_t = agg::image_accessor_wrap<input_pixfmt_t, reflect_t, reflect_t>;
using image_accessor_clip_t = agg::image_accessor_clip<input_pixfmt_t>;

using span_alloc_t = agg::span_allocator<color_type>;
using span_conv_alpha_t = span_conv_alpha<color_type>;
Expand Down Expand Up @@ -742,7 +743,8 @@ void resample(
input_buffer.attach(
(unsigned char *)input, in_width, in_height, in_width * itemsize);
input_pixfmt_t input_pixfmt(input_buffer);
image_accessor_t input_accessor(input_pixfmt);
image_accessor_wrap_t input_accessor_wrap(input_pixfmt);
image_accessor_clip_t input_accessor_clip(input_pixfmt, color_type::no_color());

agg::rendering_buffer output_buffer;
output_buffer.attach(
Expand All @@ -756,7 +758,7 @@ void resample(
rasterizer.clip_box(0, 0, out_width, out_height);

agg::path_storage path;
if (params.is_affine) {
if (params.is_affine && params.interpolation != NEAREST) {
path.move_to(0, 0);
path.line_to(in_width, 0);
path.line_to(in_width, in_height);
Expand All @@ -775,22 +777,22 @@ void resample(

if (params.interpolation == NEAREST) {
if (params.is_affine) {
using span_gen_t = typename type_mapping_t::template span_gen_nn_type<image_accessor_t, nn_affine_interpolator_t>;
using span_gen_t = typename type_mapping_t::template span_gen_nn_type<image_accessor_clip_t, nn_affine_interpolator_t>;
using span_conv_t = agg::span_converter<span_gen_t, span_conv_alpha_t>;
using nn_renderer_t = agg::renderer_scanline_aa<renderer_t, span_alloc_t, span_conv_t>;
nn_affine_interpolator_t interpolator(inverted);
span_gen_t span_gen(input_accessor, interpolator);
span_gen_t span_gen(input_accessor_clip, interpolator);
span_conv_t span_conv(span_gen, conv_alpha);
nn_renderer_t nn_renderer(renderer, span_alloc, span_conv);
agg::render_scanlines(rasterizer, scanline, nn_renderer);
} else {
using span_gen_t = typename type_mapping_t::template span_gen_nn_type<image_accessor_t, arbitrary_interpolator_t>;
using span_gen_t = typename type_mapping_t::template span_gen_nn_type<image_accessor_clip_t, arbitrary_interpolator_t>;
using span_conv_t = agg::span_converter<span_gen_t, span_conv_alpha_t>;
using nn_renderer_t = agg::renderer_scanline_aa<renderer_t, span_alloc_t, span_conv_t>;
lookup_distortion dist(
params.transform_mesh, in_width, in_height, out_width, out_height, true);
arbitrary_interpolator_t interpolator(inverted, dist);
span_gen_t span_gen(input_accessor, interpolator);
span_gen_t span_gen(input_accessor_clip, interpolator);
span_conv_t span_conv(span_gen, conv_alpha);
nn_renderer_t nn_renderer(renderer, span_alloc, span_conv);
agg::render_scanlines(rasterizer, scanline, nn_renderer);
Expand All @@ -800,22 +802,22 @@ void resample(
get_filter(params, filter);

if (params.is_affine && params.resample) {
using span_gen_t = typename type_mapping_t::template span_gen_affine_type<image_accessor_t>;
using span_gen_t = typename type_mapping_t::template span_gen_affine_type<image_accessor_wrap_t>;
using span_conv_t = agg::span_converter<span_gen_t, span_conv_alpha_t>;
using int_renderer_t = agg::renderer_scanline_aa<renderer_t, span_alloc_t, span_conv_t>;
affine_interpolator_t interpolator(inverted);
span_gen_t span_gen(input_accessor, interpolator, filter);
span_gen_t span_gen(input_accessor_wrap, interpolator, filter);
span_conv_t span_conv(span_gen, conv_alpha);
int_renderer_t int_renderer(renderer, span_alloc, span_conv);
agg::render_scanlines(rasterizer, scanline, int_renderer);
} else {
using span_gen_t = typename type_mapping_t::template span_gen_filter_type<image_accessor_t, arbitrary_interpolator_t>;
using span_gen_t = typename type_mapping_t::template span_gen_filter_type<image_accessor_wrap_t, arbitrary_interpolator_t>;
using span_conv_t = agg::span_converter<span_gen_t, span_conv_alpha_t>;
using int_renderer_t = agg::renderer_scanline_aa<renderer_t, span_alloc_t, span_conv_t>;
lookup_distortion dist(
params.transform_mesh, in_width, in_height, out_width, out_height, false);
arbitrary_interpolator_t interpolator(inverted, dist);
span_gen_t span_gen(input_accessor, interpolator, filter);
span_gen_t span_gen(input_accessor_wrap, interpolator, filter);
span_conv_t span_conv(span_gen, conv_alpha);
int_renderer_t int_renderer(renderer, span_alloc, span_conv);
agg::render_scanlines(rasterizer, scanline, int_renderer);
Expand Down