[LIBART] problem with art_rgb_svp_alpha

[Robin Becker <robin jessikat fsnet co uk>]

I'm trying to understand how and why art_rgb_svp_alpha should give such
different results for reflected vector paths

I have two paths 0 and 1 which are y symmetric around y=128 (They are
actually letter A from Adobe's Times-Roman font (as rendered by libgt1)

to each I'm doing

        svp = art_svp_from_vpath(vpath);

        art_rgb_svp_alpha(svp,
                        0,0,
                        width, height,
                        _RGBA(self->fillColor.value, self->fillOpacity),
                        buf,
                        rowstride,
                        NULL);

one appears to come out nicely aliased and the other appears completely
unaliased and horrible. Clearly this is something to do with winding
numbers or some such, but why and what can I do to get my characters to
go the right way up on my pixmaps and get the correct angular behaviour.

vpath 0:
  0: MOVETO_C, (136.262,124.004)
  1: LINETO  , (136.91,125.498)
  2: LINETO  , (137.038,125.808)
  3: LINETO  , (137.18,126.168)
  4: LINETO  , (137.243,126.354)
  5: LINETO  , (137.295,126.536)
  6: LINETO  , (137.329,126.708)
  7: LINETO  , (137.342,126.866)
  8: LINETO  , (137.337,126.979)
  9: LINETO  , (137.321,127.08)
 10: LINETO  , (137.295,127.172)
 11: LINETO  , (137.26,127.253)
 12: LINETO  , (137.214,127.326)
 13: LINETO  , (137.159,127.39)
 14: LINETO  , (137.094,127.445)
 15: LINETO  , (137.02,127.494)
 16: LINETO  , (136.937,127.535)
 17: LINETO  , (136.845,127.57)
 18: LINETO  , (136.745,127.599)
 19: LINETO  , (136.636,127.623)
 20: LINETO  , (136.393,127.657)
 21: LINETO  , (136.118,127.676)
 22: LINETO  , (136.118,128)
 23: LINETO  , (140.816,128)
 24: LINETO  , (140.816,127.676)
 25: LINETO  , (140.578,127.655)
 26: LINETO  , (140.361,127.613)
 27: LINETO  , (140.164,127.551)
 28: LINETO  , (139.985,127.47)
 29: LINETO  , (139.824,127.373)
 30: LINETO  , (139.677,127.259)
 31: LINETO  , (139.544,127.131)
 32: LINETO  , (139.423,126.99)
 33: LINETO  , (139.313,126.836)
 34: LINETO  , (139.211,126.672)
 35: LINETO  , (139.116,126.498)
 36: LINETO  , (139.026,126.317)
 37: LINETO  , (138.858,125.934)
 38: LINETO  , (138.692,125.534)
 39: LINETO  , (134.642,115.814)
 40: LINETO  , (134.318,115.814)
 41: LINETO  , (130.034,125.858)
 42: LINETO  , (129.838,126.294)
 43: LINETO  , (129.743,126.486)
 44: LINETO  , (129.648,126.661)
 45: LINETO  , (129.553,126.82)
 46: LINETO  , (129.457,126.963)
 47: LINETO  , (129.358,127.092)
 48: LINETO  , (129.256,127.206)
 49: LINETO  , (129.148,127.306)
 50: LINETO  , (129.036,127.393)
 51: LINETO  , (128.916,127.468)
 52: LINETO  , (128.789,127.531)
 53: LINETO  , (128.652,127.583)
 54: LINETO  , (128.506,127.624)
 55: LINETO  , (128.349,127.655)
 56: LINETO  , (128.18,127.676)
 57: LINETO  , (128.18,128)
 58: LINETO  , (131.924,128)
 59: LINETO  , (131.924,127.676)
 60: LINETO  , (131.673,127.654)
 61: LINETO  , (131.426,127.623)
 62: LINETO  , (131.193,127.577)
 63: LINETO  , (131.084,127.547)
 64: LINETO  , (130.981,127.51)
 65: LINETO  , (130.887,127.465)
 66: LINETO  , (130.801,127.413)
 67: LINETO  , (130.725,127.352)
 68: LINETO  , (130.661,127.281)
 69: LINETO  , (130.609,127.2)
 70: LINETO  , (130.57,127.107)
 71: LINETO  , (130.546,127.002)
 72: LINETO  , (130.538,126.884)
 73: LINETO  , (130.549,126.747)
 74: LINETO  , (130.58,126.594)
 75: LINETO  , (130.625,126.433)
 76: LINETO  , (130.682,126.268)
 77: LINETO  , (130.811,125.947)
 78: LINETO  , (130.934,125.678)
 79: LINETO  , (131.654,124.004)
 80: LINETO  , (136.262,124.004)
 81: MOVETO_C, (136.028,123.356)
 82: LINETO  , (131.924,123.356)
 83: LINETO  , (133.994,118.55)
 84: LINETO  , (136.028,123.356)
 85: END     , (4.3926e-312,9.01173e-093)

vpath 1:
  0: MOVETO_C, (136.262,131.996)
  1: LINETO  , (136.91,130.502)
  2: LINETO  , (137.038,130.192)
  3: LINETO  , (137.18,129.832)
  4: LINETO  , (137.243,129.646)
  5: LINETO  , (137.295,129.464)
  6: LINETO  , (137.329,129.292)
  7: LINETO  , (137.342,129.134)
  8: LINETO  , (137.337,129.021)
  9: LINETO  , (137.321,128.92)
 10: LINETO  , (137.295,128.828)
 11: LINETO  , (137.26,128.747)
 12: LINETO  , (137.214,128.674)
 13: LINETO  , (137.159,128.61)
 14: LINETO  , (137.094,128.555)
 15: LINETO  , (137.02,128.506)
 16: LINETO  , (136.937,128.465)
 17: LINETO  , (136.845,128.43)
 18: LINETO  , (136.745,128.401)
 19: LINETO  , (136.636,128.377)
 20: LINETO  , (136.393,128.343)
 21: LINETO  , (136.118,128.324)
 22: LINETO  , (136.118,128)
 23: LINETO  , (140.816,128)
 24: LINETO  , (140.816,128.324)
 25: LINETO  , (140.578,128.345)
 26: LINETO  , (140.361,128.387)
 27: LINETO  , (140.164,128.449)
 28: LINETO  , (139.985,128.53)
 29: LINETO  , (139.824,128.627)
 30: LINETO  , (139.677,128.741)
 31: LINETO  , (139.544,128.869)
 32: LINETO  , (139.423,129.01)
 33: LINETO  , (139.313,129.164)
 34: LINETO  , (139.211,129.328)
 35: LINETO  , (139.116,129.502)
 36: LINETO  , (139.026,129.683)
 37: LINETO  , (138.858,130.066)
 38: LINETO  , (138.692,130.466)
 39: LINETO  , (134.642,140.186)
 40: LINETO  , (134.318,140.186)
 41: LINETO  , (130.034,130.142)
 42: LINETO  , (129.838,129.706)
 43: LINETO  , (129.743,129.514)
 44: LINETO  , (129.648,129.339)
 45: LINETO  , (129.553,129.18)
 46: LINETO  , (129.457,129.037)
 47: LINETO  , (129.358,128.908)
 48: LINETO  , (129.256,128.794)
 49: LINETO  , (129.148,128.694)
 50: LINETO  , (129.036,128.607)
 51: LINETO  , (128.916,128.532)
 52: LINETO  , (128.789,128.469)
 53: LINETO  , (128.652,128.417)
 54: LINETO  , (128.506,128.376)
 55: LINETO  , (128.349,128.345)
 56: LINETO  , (128.18,128.324)
 57: LINETO  , (128.18,128)
 58: LINETO  , (131.924,128)
 59: LINETO  , (131.924,128.324)
 60: LINETO  , (131.673,128.346)
 61: LINETO  , (131.426,128.377)
 62: LINETO  , (131.193,128.423)
 63: LINETO  , (131.084,128.453)
 64: LINETO  , (130.981,128.491)
 65: LINETO  , (130.887,128.535)
 66: LINETO  , (130.801,128.587)
 67: LINETO  , (130.725,128.648)
 68: LINETO  , (130.661,128.719)
 69: LINETO  , (130.609,128.8)
 70: LINETO  , (130.57,128.893)
 71: LINETO  , (130.546,128.998)
 72: LINETO  , (130.538,129.116)
 73: LINETO  , (130.549,129.253)
 74: LINETO  , (130.58,129.406)
 75: LINETO  , (130.625,129.567)
 76: LINETO  , (130.682,129.732)
 77: LINETO  , (130.811,130.053)
 78: LINETO  , (130.934,130.322)
 79: LINETO  , (131.654,131.996)
 80: LINETO  , (136.262,131.996)
 81: MOVETO_C, (136.028,132.644)
 82: LINETO  , (131.924,132.644)
 83: LINETO  , (133.994,137.45)
 84: LINETO  , (136.028,132.644)
 85: END     , (2.49472e-091,3.66469e-043)
-- 
Robin Becker