Improved antialiased mean reduction

datashader/compiler.py

@@ -392,7 +392,7 @@ def get_cuda_mutex_call(lock: bool) -> str:
 
         args.extend([local_lk[i] for i in temps])
         if antialias:
-            args.append("aa_factor")
+            args += ["aa_factor", "prev_aa_factor"]
 
         if local_cuda_mutex and prev_local_cuda_mutex:
             # Avoid unnecessary mutex unlock and lock cycle
@@ -458,7 +458,7 @@ def get_cuda_mutex_call(lock: bool) -> str:
         body = [get_cuda_mutex_call(True)] + body + [get_cuda_mutex_call(False)]
 
     if antialias:
-        signature.insert(0, "aa_factor")
+        signature = ["aa_factor", "prev_aa_factor"] + signature
 
     if ndims is None:
         code = ('def append(x, y, {0}):\n'

datashader/glyphs/glyph.py

@@ -174,6 +174,6 @@ def _expand_aggs_and_cols(append, ndims, antialiased):
 
         # Antialiased append() calls also take aa_factor argument
         if antialiased:
-            aggs_and_cols_len -= 1
+            aggs_and_cols_len -= 2
 
         return expand_varargs(aggs_and_cols_len)

datashader/glyphs/line.py

@@ -967,15 +967,18 @@ def _full_antialias(line_width, overwrite, i, x0, x1, y0, y1,
                         prev_correction = True
                 value = 1.0 - _linearstep(0.5*(line_width - aa), halfwidth, distance)
                 value *= scale
+                prev_value = 0.0
                 if prev_correction:
                     # Already set pixel from previous segment, need to correct it
                     prev_distance = abs((x-x0)*prev_rightx + (y-y0)*prev_righty)
                     prev_value = 1.0 - _linearstep(0.5*(line_width - aa), halfwidth, prev_distance)
                     prev_value *= scale
-                    value = value - prev_value  # Correction from previous segment.
+                    if value <= prev_value:
+                        # Have already used a larger value (alpha) for this pixel.
+                        value = 0.0
                 if value > 0.0:
                     xx, yy = (y, x) if flip_xy else (x, y)
-                    append(i, xx, yy, value, *aggs_and_cols)
+                    append(i, xx, yy, value, prev_value, *aggs_and_cols)
 
     return _full_antialias
 

datashader/reductions.py

@@ -556,18 +556,18 @@
 
     @staticmethod
     @ngjit
-    def _append_antialias(x, y, agg, field, aa_factor):
+    def _append_antialias(x, y, agg, field, aa_factor, prev_aa_factor):
         if not isnull(field):
             if isnull(agg[y, x]):
-                agg[y, x] = aa_factor
+                agg[y, x] = aa_factor - prev_aa_factor
             else:
-                agg[y, x] += aa_factor
+                agg[y, x] += aa_factor - prev_aa_factor
             return 0
         return -1
 
     @staticmethod
     @ngjit
-    def _append_antialias_not_self_intersect(x, y, agg, field, aa_factor):
+    def _append_antialias_not_self_intersect(x, y, agg, field, aa_factor, prev_aa_factor):
         if not isnull(field):
             if isnull(agg[y, x]) or aa_factor > agg[y, x]:
                 agg[y, x] = aa_factor
@@ -582,16 +582,16 @@
 
     @staticmethod
     @ngjit
-    def _append_no_field_antialias(x, y, agg, aa_factor):
+    def _append_no_field_antialias(x, y, agg, aa_factor, prev_aa_factor):
         if isnull(agg[y, x]):
-            agg[y, x] = aa_factor
+            agg[y, x] = aa_factor - prev_aa_factor
         else:
-            agg[y, x] += aa_factor
+            agg[y, x] += aa_factor - prev_aa_factor
         return 0
 
     @staticmethod
     @ngjit
-    def _append_no_field_antialias_not_self_intersect(x, y, agg, aa_factor):
+    def _append_no_field_antialias_not_self_intersect(x, y, agg, aa_factor, prev_aa_factor):
         if isnull(agg[y, x]) or aa_factor > agg[y, x]:
             agg[y, x] = aa_factor
             return 0
@@ -600,7 +600,7 @@
     # GPU append functions
     @staticmethod
     @nb_cuda.jit(device=True)
-    def _append_antialias_cuda(x, y, agg, field, aa_factor):
+    def _append_antialias_cuda(x, y, agg, field, aa_factor, prev_aa_factor):
         value = field*aa_factor
         if not isnull(value):
             old = cuda_atomic_nanmax(agg, (y, x), value)
@@ -610,7 +610,7 @@
 
     @staticmethod
     @nb_cuda.jit(device=True)
-    def _append_no_field_antialias_cuda_not_self_intersect(x, y, agg, aa_factor):
+    def _append_no_field_antialias_cuda_not_self_intersect(x, y, agg, aa_factor, prev_aa_factor):
         if not isnull(aa_factor):
             old = cuda_atomic_nanmax(agg, (y, x), aa_factor)
             if isnull(old) or old < aa_factor:
@@ -627,7 +627,7 @@
 
     @staticmethod
     @nb_cuda.jit(device=True)
-    def _append_no_field_antialias_cuda(x, y, agg, aa_factor):
+    def _append_no_field_antialias_cuda(x, y, agg, aa_factor, prev_aa_factor):
         if not isnull(aa_factor):
             old = cuda_atomic_nanmax(agg, (y, x), aa_factor)
             if isnull(old) or old < aa_factor:
@@ -658,6 +658,35 @@
         return ret
 
 
+class _count_ignore_antialiasing(count):
+    """Count reduction but ignores antialiasing. Used by mean reduction.
+    """
+    def out_dshape(self, in_dshape, antialias, cuda, partitioned):
+        return dshape(ct.uint32)
+
+    def _antialias_stage_2(self, self_intersect, array_module) -> tuple[AntialiasStage2]:
+        if self_intersect:
+            return (AntialiasStage2(AntialiasCombination.SUM_1AGG, 0),)
+        else:
+            return (AntialiasStage2(AntialiasCombination.SUM_2AGG, 0),)
+
+    @staticmethod
+    @ngjit
+    def _append_antialias(x, y, agg, field, aa_factor, prev_aa_factor):
+        if not isnull(field) and prev_aa_factor == 0.0:
+            agg[y, x] += 1
+            return 0
+        return -1
+
+    @staticmethod
+    @ngjit
+    def _append_antialias_not_self_intersect(x, y, agg, field, aa_factor, prev_aa_factor):
+        if not isnull(field) and prev_aa_factor == 0.0:
+            agg[y, x] += 1
+            return 0
+        return -1
+
+
 class by(Reduction):
     """Apply the provided reduction separately per category.
 
@@ -809,7 +838,7 @@
 
     @staticmethod
     @ngjit
-    def _append_antialias(x, y, agg, field, aa_factor):
+    def _append_antialias(x, y, agg, field, aa_factor, prev_aa_factor):
         if not isnull(field):
             if isnull(agg[y, x]) or aa_factor > agg[y, x]:
                 agg[y, x] = aa_factor
@@ -824,7 +853,7 @@
 
     @staticmethod
     @ngjit
-    def _append_no_field_antialias(x, y, agg, aa_factor):
+    def _append_no_field_antialias(x, y, agg, aa_factor, prev_aa_factor):
         if isnull(agg[y, x]) or aa_factor > agg[y, x]:
             agg[y, x] = aa_factor
             return 0
@@ -926,8 +955,8 @@
 
     @staticmethod
     @ngjit
-    def _append_antialias(x, y, agg, field, aa_factor):
-        value = field*aa_factor
+    def _append_antialias(x, y, agg, field, aa_factor, prev_aa_factor):
+        value = field*(aa_factor - prev_aa_factor)
         if not isnull(value):
             # agg[y, x] cannot be null as initialised to zero.
             agg[y, x] += value
@@ -936,7 +965,7 @@
 
     @staticmethod
     @ngjit
-    def _append_antialias_not_self_intersect(x, y, agg, field, aa_factor):
+    def _append_antialias_not_self_intersect(x, y, agg, field, aa_factor, prev_aa_factor):
         value = field*aa_factor
         if not isnull(value) and value > agg[y, x]:
             # agg[y, x] cannot be null as initialised to zero.
@@ -1026,8 +1055,8 @@
 
     @staticmethod
     @ngjit
-    def _append_antialias(x, y, agg, field, aa_factor):
-        value = field*aa_factor
+    def _append_antialias(x, y, agg, field, aa_factor, prev_aa_factor):
+        value = field*(aa_factor - prev_aa_factor)
         if not isnull(value):
             if isnull(agg[y, x]):
                 agg[y, x] = value
@@ -1038,7 +1067,7 @@
 
     @staticmethod
     @ngjit
-    def _append_antialias_not_self_intersect(x, y, agg, field, aa_factor):
+    def _append_antialias_not_self_intersect(x, y, agg, field, aa_factor, prev_aa_factor):
         value = field*aa_factor
         if not isnull(value):
             if isnull(agg[y, x]) or value > agg[y, x]:
@@ -1145,7 +1174,7 @@
 
     @staticmethod
     @ngjit
-    def _append_antialias(x, y, agg, field, aa_factor):
+    def _append_antialias(x, y, agg, field, aa_factor, prev_aa_factor):
         value = field*aa_factor
         if not isnull(value) and (isnull(agg[y, x]) or value > agg[y, x]):
             agg[y, x] = value
@@ -1190,7 +1219,7 @@
 
     @staticmethod
     @ngjit
-    def _append_antialias(x, y, agg, field, aa_factor):
+    def _append_antialias(x, y, agg, field, aa_factor, prev_aa_factor):
         value = field*aa_factor
         if not isnull(value) and (isnull(agg[y, x]) or value > agg[y, x]):
             agg[y, x] = value
@@ -1200,7 +1229,7 @@
     # GPU append functions
     @staticmethod
     @nb_cuda.jit(device=True)
-    def _append_antialias_cuda(x, y, agg, field, aa_factor):
+    def _append_antialias_cuda(x, y, agg, field, aa_factor, prev_aa_factor):
         value = field*aa_factor
         if not isnull(value):
             old = cuda_atomic_nanmax(agg, (y, x), value)
@@ -1247,7 +1276,7 @@
         ``NaN`` values in the column are skipped.
     """
     def _build_bases(self, cuda, partitioned):
-        return (_sum_zero(self.column), count(self.column))
+        return (_sum_zero(self.column), _count_ignore_antialiasing(self.column))
 
     @staticmethod
     def _finalize(bases, cuda=False, **kwargs):
@@ -1365,7 +1394,7 @@
 
     @staticmethod
     @ngjit
-    def _append_antialias(x, y, agg, field, aa_factor):
+    def _append_antialias(x, y, agg, field, aa_factor, prev_aa_factor):
         value = field*aa_factor
         if not isnull(value) and (isnull(agg[y, x]) or value > agg[y, x]):
             agg[y, x] = value
@@ -1403,7 +1432,7 @@
 
     @staticmethod
     @ngjit
-    def _append_antialias(x, y, agg, field, aa_factor):
+    def _append_antialias(x, y, agg, field, aa_factor, prev_aa_factor):
         value = field*aa_factor
         if not isnull(value) and (isnull(agg[y, x]) or value > agg[y, x]):
             agg[y, x] = value
@@ -1512,7 +1541,7 @@
 
     @staticmethod
     @ngjit
-    def _append_antialias(x, y, agg, field, aa_factor):
+    def _append_antialias(x, y, agg, field, aa_factor, prev_aa_factor):
         value = field*aa_factor
         if not isnull(value):
             # Check final value first for quick abort.
@@ -1549,7 +1578,7 @@
 
     @staticmethod
     @ngjit
-    def _append_antialias(x, y, agg, field, aa_factor):
+    def _append_antialias(x, y, agg, field, aa_factor, prev_aa_factor):
         value = field*aa_factor
         if not isnull(value):
             # Always inserts at front of agg's third dimension.
@@ -1584,7 +1613,7 @@
 
     @staticmethod
     @ngjit
-    def _append_antialias(x, y, agg, field, aa_factor):
+    def _append_antialias(x, y, agg, field, aa_factor, prev_aa_factor):
         value = field*aa_factor
         if not isnull(value):
             # Linear walk along stored values.
@@ -1664,7 +1693,7 @@
 
     @staticmethod
     @ngjit
-    def _append_antialias(x, y, agg, field, aa_factor):
+    def _append_antialias(x, y, agg, field, aa_factor, prev_aa_factor):
         value = field*aa_factor
         if not isnull(value):
             # Linear walk along stored values.
@@ -1841,7 +1870,7 @@
 
     @staticmethod
     @ngjit
-    def _append_antialias(x, y, agg, field, aa_factor, update_index):
+    def _append_antialias(x, y, agg, field, aa_factor, prev_aa_factor, update_index):
         # Ignore aa_factor.
         if agg.ndim > 2:
             shift_and_insert(agg[y, x], field, update_index)
@@ -1850,7 +1879,7 @@
 
     @staticmethod
     @nb_cuda.jit(device=True)
-    def _append_antialias_cuda(x, y, agg, field, aa_factor, update_index):
+    def _append_antialias_cuda(x, y, agg, field, aa_factor, prev_aa_factor, update_index):
         # Ignore aa_factor
         if agg.ndim > 2:
             cuda_shift_and_insert(agg[y, x], field, update_index)
@@ -2172,7 +2201,7 @@
 
     @staticmethod
     @ngjit
-    def _append_antialias(x, y, agg, field, aa_factor):
+    def _append_antialias(x, y, agg, field, aa_factor, prev_aa_factor):
         # field is int64 row index
         # Ignore aa_factor
         if field > agg[y, x]:
@@ -2230,7 +2259,7 @@
 
     @staticmethod
     @ngjit
-    def _append_antialias(x, y, agg, field, aa_factor):
+    def _append_antialias(x, y, agg, field, aa_factor, prev_aa_factor):
         # field is int64 row index
         # Ignore aa_factor
         if field != -1 and (agg[y, x] == -1 or field < agg[y, x]):
@@ -2326,7 +2355,7 @@
 
     @staticmethod
     @ngjit
-    def _append_antialias(x, y, agg, field, aa_factor):
+    def _append_antialias(x, y, agg, field, aa_factor, prev_aa_factor):
         # field is int64 row index
         # Ignoring aa_factor
         if field != -1:
@@ -2409,7 +2438,7 @@
 
     @staticmethod
     @ngjit
-    def _append_antialias(x, y, agg, field, aa_factor):
+    def _append_antialias(x, y, agg, field, aa_factor, prev_aa_factor):
         # field is int64 row index
         # Ignoring aa_factor
         if field != -1: