Initial import

test/dsp/tty/rgb2ansi_test.c

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+/*-*- mode:c;indent-tabs-mode:nil;c-basic-offset:2;tab-width:8;coding:utf-8 -*-│
+│vi: set net ft=c ts=2 sts=2 sw=2 fenc=utf-8                                :vi│
+╞══════════════════════════════════════════════════════════════════════════════╡
+│ Copyright 2020 Justine Alexandra Roberts Tunney                              │
+│                                                                              │
+│ This program is free software; you can redistribute it and/or modify         │
+│ it under the terms of the GNU General Public License as published by         │
+│ the Free Software Foundation; version 2 of the License.                      │
+│                                                                              │
+│ This program is distributed in the hope that it will be useful, but          │
+│ WITHOUT ANY WARRANTY; without even the implied warranty of                   │
+│ MERCHANTABILITY or FITNESS FOR A PARTICULAR PURPOSE. See the GNU             │
+│ General Public License for more details.                                     │
+│                                                                              │
+│ You should have received a copy of the GNU General Public License            │
+│ along with this program; if not, write to the Free Software                  │
+│ Foundation, Inc., 51 Franklin Street, Fifth Floor, Boston, MA                │
+│ 02110-1301 USA                                                               │
+╚─────────────────────────────────────────────────────────────────────────────*/
+#include "dsp/tty/quant.h"
+#include "libc/testlib/testlib.h"
+
+struct TtyRgb res;
+
+TEST(rgb2ansi, testDesaturatedPurple_isQuantizedBetterThanEuclideanDistance) {
+  ttyquantinit(kTtyQuantXterm256, kTtyQuantRgb, kTtyBlocksUnicode);
+
+  /*
+   * the challenge to the xterm256 palette is that it was likely
+   * intended for just syntax highlighting, rather than accurately
+   * modeling the natural phenomenon of illumination.
+   *
+   * as a syntax highlighting palette, it focuses mostly on bright
+   * saturated colors, while also providing a really good greyscale for
+   * everything else.
+   *
+   * as such, if one were to project the colors of this palette into a
+   * three-dimensional space, we might see something like an HSV cone,
+   * where all the color samples are projected mostly around the outside
+   * of the cone, and the greyscale dots tracing through the middle.
+   *
+   * if we want to convert an a real color into an xterm color, we can
+   * use euclidean distance functions to pick the closest color, such as
+   * sum of squared distance. however this will only work well if it's
+   * either a pure grey color, or a bright saturated one.
+   *
+   * but euclidean distance doesnt work well for the sorts of colors
+   * that are generally used for things like film, which conservatively
+   * edits for the colors more towards the middle of the space; and as
+   * such, which basically causes the distance function to pick greys
+   * for almost everything.
+   */
+
+  res = rgb2tty(0x56, 0x38, 0x66);
+
+  /* EXPECT_NE(0x4e, res.r); */
+  /* EXPECT_NE(0x4e, res.g); */
+  /* EXPECT_NE(0x4e, res.b); */
+  /* EXPECT_NE(239, res.xt); */
+
+  /* EXPECT_EQ(0x5f, res.r); */
+  /* EXPECT_EQ(0x00, res.g); */
+  /* EXPECT_EQ(0x5f, res.b); */
+  /* EXPECT_EQ(53, res.xt); */
+}