#!/usr/bin/env python
# Copyright 2018 The Chromium Authors
# Use of this source code is governed by a BSD-style license that can be
# found in the LICENSE file.
"""
Generates Java code to declare SPLINE_POSITION and SPLINE_TIME as precomputed
array.
Run this and paste the output into //chrome/android/java/src/org/chromium/
chrome/browser/compositor/layouts/phone/stack/StackScroller.java
"""
from __future__ import print_function
import math
import sys
def Main():
# Keep these in sync with the values in //chrome/android/java/src/org/
# chromium/chrome/browser/compositor/layouts/phone/stack/StackScroller.java
NB_SAMPLES = 100
INFLEXION = 0.35 # Tension lines cross at (INFLEXION, 1)
START_TENSION = 0.5
END_TENSION = 1.0
P1 = START_TENSION * INFLEXION
P2 = 1.0 - END_TENSION * (1.0 - INFLEXION)
spline_time = []
spline_position = []
xMin = 0.0
yMin = 0.0
for i in range(NB_SAMPLES):
alpha = float(i) / NB_SAMPLES
xMax = 1.0
while 1:
x = xMin + (xMax - xMin) / 2.0
coef = 3.0 * x * (1.0 - x)
tx = coef * ((1.0 - x) * P1 + x * P2) + x * x * x
if math.fabs(tx - alpha) < 1E-5:
break
if tx > alpha:
xMax = x
else:
xMin = x
spline_position.append(coef * ((1.0 - x) * START_TENSION + x)
+ x * x * x)
yMax = 1.0
while 1:
y = yMin + (yMax - yMin) / 2.0
coef = 3.0 * y * (1.0 - y)
dy = coef * ((1.0 - y) * START_TENSION + y) + y * y * y
if math.fabs(dy - alpha) < 1E-5:
break
if dy > alpha:
yMax = y
else:
yMin = y
spline_time.append(coef * ((1.0 - y) * P1 + y * P2) + y * y * y)
spline_position.append(1.0)
spline_time.append(1.0)
print(WriteJavaArrayDeclaration('SPLINE_POSITION', spline_position))
print(WriteJavaArrayDeclaration('SPLINE_TIME', spline_time))
return 0
def WriteJavaArrayDeclaration(name, float_list):
MAX_CHARS_PER_LINE = 100
INDENT_LEVELS = 2
SPACES_PER_INDENT_LEVEL = 4
DECLARATION_PREAMBLE = ' ' * SPACES_PER_INDENT_LEVEL * INDENT_LEVELS
VALUES_PREAMBLE = ' ' * SPACES_PER_INDENT_LEVEL * (INDENT_LEVELS + 2)
# Default precision is 6 decimal plates.
FLOAT_LENGTH = len('0.123456, ')
# +1 accounts for the trimmed space at the end.
FLOATS_PER_LINE = ((MAX_CHARS_PER_LINE - len(VALUES_PREAMBLE) + 1)
/ FLOAT_LENGTH)
chunks = []
for i in xrange(0, len(float_list), FLOATS_PER_LINE):
float_chunk = float_list[i : i + FLOATS_PER_LINE]
values = ', '.join(['%ff' % f for f in float_chunk])
chunks.append(VALUES_PREAMBLE + values)
s = DECLARATION_PREAMBLE + 'private static final float[] %s = {\n' % name
s += ',\n'.join(chunks)
s += '\n'
s += DECLARATION_PREAMBLE + '};'
return s
if __name__ == '__main__':
sys.exit(Main())
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