In certain cases, the coordinates used for pattern rendering can go...

skia/sgl/SkBitmapProcState_matrixProcs.cpp

 #include "SkBitmapProcState.h"
 #include "SkPerspIter.h"
 #include "SkShader.h"
 
 void decal_nofilter_scale(uint32_t dst[], SkFixed fx, SkFixed dx, int count);
 void decal_filter_scale(uint32_t dst[], SkFixed fx, SkFixed dx, int count);
 
 #ifdef SK_CPU_BENDIAN
     #define PACK_TWO_SHORTS(pri, sec) ((pri) << 16 | (sec))
 #else
@@ skipping 19 matching lines @@
 #define CHECK_FOR_DECAL
 #define TILEX_TRANS(x, max)     SkClampMax(x, max)
 #define TILEY_TRANS(y, max)     SkClampMax(y, max)
 #include "SkBitmapProcState_matrix.h"
 
 #define MAKENAME(suffix)        RepeatX_RepeatY ## suffix
 #define TILEX_PROCF(fx, max)    (((fx) & 0xFFFF) * ((max) + 1) >> 16)
 #define TILEY_PROCF(fy, max)    (((fy) & 0xFFFF) * ((max) + 1) >> 16)
 #define TILEX_LOW_BITS(fx, max) ((((fx) & 0xFFFF) * ((max) + 1) >> 12) & 0xF)
 #define TILEY_LOW_BITS(fy, max) ((((fy) & 0xFFFF) * ((max) + 1) >> 12) & 0xF)
-#define TILEX_TRANS(x, max)     ((x) % ((max) + 1))
-#define TILEY_TRANS(y, max)     ((y) % ((max) + 1))
+#define SK_MOD(a, b)            (((a)%(b)) < 0 ? ((a)%(b) + (b)) : (a)%(b))
+#define TILEX_TRANS(x, max)     (SK_MOD((x), ((max) + 1)))
+#define TILEY_TRANS(y, max)     (SK_MOD((y), ((max) + 1)))
 #include "SkBitmapProcState_matrix.h"
 
 #define MAKENAME(suffix)        GeneralXY ## suffix
 #define PREAMBLE(state)         SkBitmapProcState::FixedTileProc tileProcX = (state).fTileProcX; \
                                 SkBitmapProcState::FixedTileProc tileProcY = (state).fTileProcY
 #define PREAMBLE_PARAM_X        , SkBitmapProcState::FixedTileProc tileProcX
 #define PREAMBLE_PARAM_Y        , SkBitmapProcState::FixedTileProc tileProcY
 #define PREAMBLE_ARG_X          , tileProcX
 #define PREAMBLE_ARG_Y          , tileProcY
 #define TILEX_PROCF(fx, max)    (tileProcX(fx, max) >> 16)
@@ skipping 188 matching lines @@
     while ((count -= width) >= 0)
         for (i = 0; i < width; i++)
             *xx++ = SkToU16(i);
 
     // final cleanup run
     count += width;
     for (i = 0; i < count; i++)
         *xx++ = SkToU16(i);
 }