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Support scaling down bits (e.g. from 10 to 8) with scale_xbits_to_8bits() doing a bit shift

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This commit is contained in:
David Capello 2023-10-25 16:38:23 -03:00
parent 4387432ad3
commit 9800d0ba1a
2 changed files with 21 additions and 6 deletions
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21
src/doc/color_scales.h
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@ -1,5 +1,5 @@
// Aseprite Document Library // Aseprite Document Library
// Copyright (C) 2020-2022 Igara Studio S.A. // Copyright (C) 2020-2023 Igara Studio S.A.
// Copyright (C) 2001-2016 David Capello // Copyright (C) 2001-2016 David Capello
// //
// This file is released under the terms of the MIT license. // This file is released under the terms of the MIT license.
@ -13,22 +13,23 @@
namespace doc { namespace doc {
inline int scale_3bits_to_8bits(const int v) { constexpr inline int scale_3bits_to_8bits(const int v) {
ASSERT(v >= 0 && v < 8); ASSERT(v >= 0 && v < 8);
return (v << 5) | (v << 2) | (v >> 1); return (v << 5) | (v << 2) | (v >> 1);
} }
inline int scale_5bits_to_8bits(const int v) { constexpr inline int scale_5bits_to_8bits(const int v) {
ASSERT(v >= 0 && v < 32); ASSERT(v >= 0 && v < 32);
return (v << 3) | (v >> 2); return (v << 3) | (v >> 2);
} }
inline int scale_6bits_to_8bits(const int v) { constexpr inline int scale_6bits_to_8bits(const int v) {
ASSERT(v >= 0 && v < 64); ASSERT(v >= 0 && v < 64);
return (v << 2) | (v >> 4); return (v << 2) | (v >> 4);
} }
inline int scale_xbits_to_8bits(const int x, const int v) { template<typename T>
constexpr inline int scale_xbits_to_8bits(const int x, const T v) {
switch (x) { switch (x) {
case 3: case 3:
return scale_3bits_to_8bits(v); return scale_3bits_to_8bits(v);
@ -36,8 +37,16 @@ namespace doc {
return scale_5bits_to_8bits(v); return scale_5bits_to_8bits(v);
case 6: case 6:
return scale_6bits_to_8bits(v); return scale_6bits_to_8bits(v);
default:
if (x < 8) {
return (255.0 * double(v) / double((T(1)<<x)-1));
}
else {
// To reduce precision (e.g. from 10 bits to 8 bits) we just
// remove least significant bits.
return v >> (x - 8);
}
} }
return (int)(255.0 / (double(1<<x) - 1.0) * (double)v);
} }
} // namespace doc } // namespace doc

6
src/doc/color_scales_tests.cpp
View File

@ -34,6 +34,12 @@ TEST(ColorScales, MatchValues)
} }
} }
TEST(ColorScales, TenBits)
{
EXPECT_EQ(0xff, scale_xbits_to_8bits(10, 0x3ff));
EXPECT_EQ(0x7f, scale_xbits_to_8bits(10, 0x1ff));
}
int main(int argc, char** argv) int main(int argc, char** argv)
{ {
::testing::InitGoogleTest(&argc, argv); ::testing::InitGoogleTest(&argc, argv);