add table pregeneration script for pmetric

experimental/skpdiff/generate_pmetric_tables.py

Index: experimental/skpdiff/generate_pmetric_tables.py
diff --git a/experimental/skpdiff/generate_pmetric_tables.py b/experimental/skpdiff/generate_pmetric_tables.py
new file mode 100755
index 0000000000000000000000000000000000000000..12c226347f5c2a3eccce8e8eaf993d8cc1e0b8d1
--- /dev/null
+++ b/experimental/skpdiff/generate_pmetric_tables.py
@@ -0,0 +1,149 @@
+#!/usr/bin/python
+# -*- coding: utf-8 -*-
+
+from __future__ import print_function
+from math import *
+
+
+COPYRIGHT = '''/*
+ * Copyright 2013 Google Inc.
+ *
+ * Use of this source code is governed by a BSD-style license that can be
+ * found in the LICENSE file.
+ */'''
+
+
+HELP = '// To regenerate SkPMetricUtil_generated.h, simply run ./generate_pmetric_tables.py'
+
+
+# From Barten SPIE 1989
+def contrast_sensitivity(cycles_per_degree, luminance):
+    a = 440.0 * pow(1.0 + 0.7 / luminance, -0.2)
+    b = 0.3 * pow(1 + 100.0 / luminance, 0.15)
+    return a * cycles_per_degree * exp(-b * cycles_per_degree) * sqrt(1.0 + 0.06 * exp(b * cycles_per_degree))
+
+
+# From Ward Larson Siggraph 1997
+def threshold_vs_intensity(adaptation_luminance):
+    log_lum = float('-inf') # Works in Python 2.6+
+    try:
+        log_lum = log10(adaptation_luminance)
+    except ValueError:
+        pass
+
+    x = 0.0
+
+    if log_lum < -3.94:
+        x = -2.86
+
+    elif log_lum < -1.44:
+        x = pow(0.405 * log_lum + 1.6, 2.18) - 2.86
+
+    elif log_lum < -0.0184:
+        x = log_lum - 0.395
+
+    elif log_lum < 1.9:
+        x = pow(0.249 * log_lum + 0.65, 2.7) - 0.72
+
+    else:
+        x = log_lum - 1.255
+
+    return pow(10.0, x)
+
+
+# From Daly 1993
+def visual_mask(contrast):
+    x = pow(392.498 * contrast, 0.7)
+    x = pow(0.0153 * x, 4.0)
+    return pow(1.0 + x, 0.25)
+
+
+# float gCubeRootTable[]
+CUBE_ROOT_ACCESS_FUNCTION = '''
+float get_cube_root(float value) {
+    SkASSERT(value >= 0.0f);
+    SkASSERT(value * 1023.0f < 1024.0f);
+    return gCubeRootTable[(int)(value * 1023.0f)];
+}
+'''
+def generate_cube_root_table(stream):
+    print('static float gCubeRootTable[] = {', end='', file=stream)
+    for i in range(1024):
+        if i % 6 == 0:
+            print('\n    ', end='', file=stream)
+        print("%.10f" % pow(i / 1024.0, 1.0 / 3.0), end='f,', file=stream)
+    print('\n};', end='', file=stream)
+    print(CUBE_ROOT_ACCESS_FUNCTION, file=stream)
+
+
+# float gGammaTable[]
+GAMMA_ACCESS_FUNCTION = '''
+float get_gamma(unsigned char value) {
+    return gGammaTable[value];
+}
+'''
+def generate_gamma_table(stream):
+    print('static float gGammaTable[] = {', end='', file=stream)
+    for i in range(256):
+        if i % 6 == 0:
+            print('\n    ', end='', file=stream)
+        print("%.10f" % pow(i / 255.0, 2.2), end='f,', file=stream)
+    print('\n};', end='', file=stream)
+    print(GAMMA_ACCESS_FUNCTION, file=stream)
+
+
+# float gTVITable[]
+TVI_ACCESS_FUNCTION = '''
+float get_threshold_vs_intensity(float value) {
+    SkASSERT(value >= 0.0f);
+    SkASSERT(value < 100.0f);
+    return gTVITable[(int)(value * 100.0f)];
+}
+'''
+def generate_tvi_table(stream):
+    print('static float gTVITable[] = {', end='', file=stream)
+    for i in range(10000):
+        if i % 6 == 0:
+            print('\n    ', end='', file=stream)
+        print("%.10f" % threshold_vs_intensity(i / 100.0), end='f,', file=stream)
+    print('\n};', end='', file=stream)
+    print(TVI_ACCESS_FUNCTION, file=stream)
+
+
+# float gVisualMaskTable[]
+VISUAL_MASK_DOMAIN = 4000
+VISUAL_MASK_ACCESS_FUNCTION = '''
+float get_visual_mask(float value) {{
+    SkASSERT(value >= 0.0f);
+    SkASSERT(value < {}.0f);
+    return gVisualMaskTable[(int)value];
+}}'''
+def generate_visual_mask_table(stream):
+    print('static float gVisualMaskTable[] = {', end='', file=stream)
+    for i in range(VISUAL_MASK_DOMAIN):
+        if i % 6 == 0:
+            print('\n    ', end='', file=stream)
+        print("%.10f" % visual_mask(i), end='f,', file=stream)
+    print('\n};', end='', file=stream)
+    print(VISUAL_MASK_ACCESS_FUNCTION.format(VISUAL_MASK_DOMAIN), file=stream)
+
+
+def generate_lookup_tables(stream):
+    print(COPYRIGHT, file=stream)
+    print(HELP, file=stream)
+    print('namespace SkPMetricUtil {', file=stream)
+    generate_cube_root_table(stream)
+    generate_gamma_table(stream)
+    generate_tvi_table(stream)
+    generate_visual_mask_table(stream)
+    print('}', file=stream)
+
+
+def main():
+    pmetric_util_out = open('SkPMetricUtil_generated.h', 'wb')
+    generate_lookup_tables(pmetric_util_out)
+    pmetric_util_out.close()
+
+
+if __name__ == '__main__':
+    main()