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Commit 0e2b40f

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jkseppanjkseppan
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Implement alpha for Gouraud shading
1 parent d135d87 commit 0e2b40f
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‎lib/matplotlib/backends/backend_pdf.py

Copy file name to clipboardExpand all lines: lib/matplotlib/backends/backend_pdf.py
+133-22Lines changed: 133 additions & 22 deletions
Original file line numberDiff line numberDiff line change
@@ -481,7 +481,7 @@ def __init__(self, filename, metadata=None):
481481
self.pagesObject = self.reserveObject('pages')
482482
self.pageList = []
483483
self.fontObject = self.reserveObject('fonts')
484-
self.alphaStateObject = self.reserveObject('extended graphics states')
484+
self.extGStateObject = self.reserveObject('extended graphics states')
485485
self.hatchObject = self.reserveObject('tiling patterns')
486486
self.gouraudObject = self.reserveObject('Gouraud triangles')
487487
self.XObjectObject = self.reserveObject('external objects')
@@ -519,6 +519,9 @@ def __init__(self, filename, metadata=None):
519519

520520
self.alphaStates = {} # maps alpha values to graphics state objects
521521
self.alphaStateName = (Name(f'A{i}') for i in itertools.count(1))
522+
self.softmaskStates = {}
523+
self.softmaskStateName = (Name(f'SM{i}') for i in itertools.count(1))
524+
self.softmaskGroups = []
522525
# reproducible writeHatches needs an ordered dict:
523526
self.hatchPatterns = collections.OrderedDict()
524527
self.hatchPatternName = (Name(f'H{i}') for i in itertools.count(1))
@@ -543,7 +546,7 @@ def __init__(self, filename, metadata=None):
543546
# ColorSpace Pattern Shading Properties
544547
resources = {'Font': self.fontObject,
545548
'XObject': self.XObjectObject,
546-
'ExtGState': self.alphaStateObject,
549+
'ExtGState': self.extGStateObject,
547550
'Pattern': self.hatchObject,
548551
'Shading': self.gouraudObject,
549552
'ProcSet': procsets}
@@ -593,9 +596,8 @@ def finalize(self):
593596

594597
self.endStream()
595598
self.writeFonts()
596-
self.writeObject(
597-
self.alphaStateObject,
598-
{val[0]: val[1] for val in self.alphaStates.values()})
599+
self.writeExtGSTates()
600+
self.writeSoftmaskGroups()
599601
self.writeHatches()
600602
self.writeGouraudTriangles()
601603
xobjects = {
@@ -1219,6 +1221,72 @@ def alphaState(self, alpha):
12191221
'CA': alpha[0], 'ca': alpha[1]})
12201222
return name
12211223

1224+
def softmaskState(self, smask):
1225+
"""Return the name of an ExtGState that sets the soft mask to the given shading.
1226+
1227+
Parameters
1228+
----------
1229+
smask : Reference
1230+
reference to a shading in DeviceGray color space, whose luminosity is
1231+
to be used as the alpha channel
1232+
1233+
Returns
1234+
-------
1235+
Name
1236+
"""
1237+
1238+
state = self.softmaskStates.get(smask, None)
1239+
if state is not None:
1240+
return state[0]
1241+
1242+
name = next(self.softmaskStateName)
1243+
groupOb = self.reserveObject('transparency group for soft mask')
1244+
self.softmaskStates[smask] = (
1245+
name,
1246+
{
1247+
'Type': Name('ExtGState'),
1248+
'AIS': False,
1249+
'SMask': {
1250+
'Type': Name('Mask'),
1251+
'S': Name('Luminosity'),
1252+
'BC': [1],
1253+
'G': groupOb
1254+
}
1255+
}
1256+
)
1257+
self.softmaskGroups.append((
1258+
groupOb,
1259+
{
1260+
'Type': Name('XObject'),
1261+
'Subtype': Name('Form'),
1262+
'FormType': 1,
1263+
'Group': {
1264+
'S': Name('Transparency'),
1265+
'CS': Name('DeviceGray')
1266+
},
1267+
'Matrix': [1, 0, 0, 1, 0, 0],
1268+
'Resources': {'Shading': {'S': smask}},
1269+
'BBox': [0, 0, 1, 1]
1270+
},
1271+
[Name('S'), Op.shading]
1272+
))
1273+
return name
1274+
1275+
def writeExtGSTates(self):
1276+
self.writeObject(
1277+
self.extGStateObject,
1278+
dict(itertools.chain(
1279+
self.alphaStates.values(),
1280+
self.softmaskStates.values()
1281+
))
1282+
)
1283+
1284+
def writeSoftmaskGroups(self):
1285+
for ob, attributes, content in self.softmaskGroups:
1286+
self.beginStream(ob.id, None, attributes)
1287+
self.output(*content)
1288+
self.endStream()
1289+
12221290
def hatchPattern(self, hatch_style):
12231291
# The colors may come in as numpy arrays, which aren't hashable
12241292
if hatch_style is not None:
@@ -1276,18 +1344,39 @@ def writeHatches(self):
12761344
self.writeObject(self.hatchObject, hatchDict)
12771345

12781346
def addGouraudTriangles(self, points, colors):
1347+
"""Add a Gouraud triangle shading
1348+
1349+
Parameters
1350+
----------
1351+
1352+
points : np.ndarray
1353+
triangle vertices, shape (n, 3, 2)
1354+
where n = number of triangles, 3 = vertices, 2 = x, y
1355+
colors : np.ndarray
1356+
vertex colors, shape (n, 3, 1) or (n, 3, 4)
1357+
as with points, but last dimension is either (gray,) or (r, g, b, alpha)
1358+
1359+
Returns
1360+
-------
1361+
Name, Reference
1362+
"""
12791363
name = Name('GT%d' % len(self.gouraudTriangles))
1280-
self.gouraudTriangles.append((name, points, colors))
1281-
return name
1364+
ob = self.reserveObject(f'Gouraud triangle {name}')
1365+
self.gouraudTriangles.append((name, ob, points, colors))
1366+
return name, ob
12821367

12831368
def writeGouraudTriangles(self):
12841369
gouraudDict = dict()
1285-
for name, points, colors in self.gouraudTriangles:
1286-
ob = self.reserveObject('Gouraud triangle')
1370+
for name, ob, points, colors in self.gouraudTriangles:
12871371
gouraudDict[name] = ob
12881372
shape = points.shape
12891373
flat_points = points.reshape((shape[0] * shape[1], 2))
1290-
flat_colors = colors.reshape((shape[0] * shape[1], 4))
1374+
colordim = colors.shape[2]
1375+
assert colordim in (1, 4)
1376+
flat_colors = colors.reshape((shape[0] * shape[1], colordim))
1377+
if colordim == 4:
1378+
# strip the alpha channel
1379+
colordim = 3
12911380
points_min = np.min(flat_points, axis=0) - (1 << 8)
12921381
points_max = np.max(flat_points, axis=0) + (1 << 8)
12931382
factor = 0xffffffff / (points_max - points_min)
@@ -1298,21 +1387,20 @@ def writeGouraudTriangles(self):
12981387
'BitsPerCoordinate': 32,
12991388
'BitsPerComponent': 8,
13001389
'BitsPerFlag': 8,
1301-
'ColorSpace': Name('DeviceRGB'),
1302-
'AntiAlias': True,
1303-
'Decode': [points_min[0], points_max[0],
1304-
points_min[1], points_max[1],
1305-
0, 1, 0, 1, 0, 1]
1390+
'ColorSpace': Name('DeviceRGB' if colordim == 3 else 'DeviceGray'),
1391+
'AntiAlias': False,
1392+
'Decode': ([points_min[0], points_max[0], points_min[1], points_max[1]]
1393+
+ [0, 1] * colordim),
13061394
})
13071395

13081396
streamarr = np.empty(
13091397
(shape[0] * shape[1],),
13101398
dtype=[('flags', 'u1'),
13111399
('points', '>u4', (2,)),
1312-
('colors', 'u1', (3,))])
1400+
('colors', 'u1', (colordim,))])
13131401
streamarr['flags'] = 0
13141402
streamarr['points'] = (flat_points - points_min) * factor
1315-
streamarr['colors'] = flat_colors[:, :3] * 255.0
1403+
streamarr['colors'] = flat_colors[:, :colordim] * 255.0
13161404

13171405
self.write(streamarr.tostring())
13181406
self.endStream()
@@ -1808,20 +1896,43 @@ def draw_gouraud_triangle(self, gc, points, colors, trans):
18081896

18091897
def draw_gouraud_triangles(self, gc, points, colors, trans):
18101898
assert len(points) == len(colors)
1899+
if len(points) == 0:
1900+
return
18111901
assert points.ndim == 3
18121902
assert points.shape[1] == 3
18131903
assert points.shape[2] == 2
18141904
assert colors.ndim == 3
18151905
assert colors.shape[1] == 3
1816-
assert colors.shape[2] == 4
1817-
1906+
assert colors.shape[2] in (1, 4)
1907+
18181908
shape = points.shape
18191909
points = points.reshape((shape[0] * shape[1], 2))
18201910
tpoints = trans.transform(points)
18211911
tpoints = tpoints.reshape(shape)
1822-
name = self.file.addGouraudTriangles(tpoints, colors)
1823-
self.check_gc(gc)
1824-
self.file.output(name, Op.shading)
1912+
name, _ = self.file.addGouraudTriangles(tpoints, colors)
1913+
output = self.file.output
1914+
1915+
if colors.shape[2] == 1:
1916+
# grayscale
1917+
gc.set_alpha(1.0)
1918+
self.check_gc(gc)
1919+
output(name, Op.shading)
1920+
return
1921+
1922+
alpha = colors[0, 0, 3]
1923+
if np.allclose(alpha, colors[:, :, 3]):
1924+
# single alpha value
1925+
gc.set_alpha(alpha)
1926+
self.check_gc(gc)
1927+
output(name, Op.shading)
1928+
else:
1929+
# varying alpha: use a soft mask
1930+
alpha = colors[:, :, 3][:, :, None]
1931+
_, smaskOb = self.file.addGouraudTriangles(tpoints, alpha)
1932+
gstate = self.file.softmaskState(smaskOb)
1933+
output(Op.gsave, gstate, Op.setgstate,
1934+
name, Op.shading,
1935+
Op.grestore)
18251936

18261937
def _setup_textpos(self, x, y, angle, oldx=0, oldy=0, oldangle=0):
18271938
if angle == oldangle == 0:

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