Fix bug where the interpolation endpoint was one step further than correct

ayshih · ayshih · commit 632e4e381ccd · 2026-01-08T10:46:53.000-05:00
diff --git a/extern/agg24-svn/include/agg_span_interpolator_linear.h b/extern/agg24-svn/include/agg_span_interpolator_linear.h
@@ -53,6 +53,10 @@ namespace agg
         //----------------------------------------------------------------
         void begin(double x, double y, unsigned len)
         {
+#ifdef MPL_FIX_AGG_INTERPOLATION_ENDPOINT_BUG
+            len -= 1;
+#endif
+
             double tx;
             double ty;
 
@@ -75,6 +79,10 @@ namespace agg
         //----------------------------------------------------------------
         void resynchronize(double xe, double ye, unsigned len)
         {
+#ifdef MPL_FIX_AGG_INTERPOLATION_ENDPOINT_BUG
+            len -= 1;
+#endif
+
             m_trans->transform(&xe, &ye);
             m_li_x = dda2_line_interpolator(m_li_x.y(), iround(xe * subpixel_scale), len);
             m_li_y = dda2_line_interpolator(m_li_y.y(), iround(ye * subpixel_scale), len);
diff --git a/meson.build b/meson.build
@@ -33,6 +33,7 @@ project(
 
 # Enable bug fixes in Agg
 add_project_arguments('-DMPL_FIX_AGG_IMAGE_FILTER_LUT_BUGS', language : 'cpp')
+add_project_arguments('-DMPL_FIX_AGG_INTERPOLATION_ENDPOINT_BUG', language : 'cpp')
 
 cc = meson.get_compiler('c')
 cpp = meson.get_compiler('cpp')
