draw565: Add lighten/darken functions

Add functions to generate shades from a single (usually theme provided)
basic palette colour.

Signed-off-by: Daniel Thompson <daniel@redfelineninja.org.uk>

wasp/boards/simulator/test_unit.py

@@ -0,0 +1,41 @@
+import draw565
+import pytest
+
+@pytest.fixture
+def draw():
+    """Provide a RGB565 drawing surface.
+
+    Currently most of the draw565 functions will not work since we haven't
+    mocked up the display. This limits the testing that we can perform.
+    """
+    d = draw565.Draw565(None)
+
+    return d
+
+def test_lighten(draw):
+    assert draw.lighten(0b00000_000000_00000         ) == 0b00001_000010_00001
+    assert draw.lighten(0b00000_000000_00000, 0b00001) == 0b00001_000010_00001
+    assert draw.lighten(0b00000_000000_00000, 0b00100) == 0b00100_001000_00100
+
+    assert draw.lighten(0b10000_100000_10000, 0b10000) == 0b11111_111111_11111
+    assert draw.lighten(0b11110_111100_11110, 0b00001) == 0b11111_111110_11111
+    assert draw.lighten(0b11110_111101_11110, 0b00001) == 0b11111_111111_11111
+
+    assert draw.lighten(0b11111_111111_11111, 0b00001) == 0b11111_111111_11111
+
+    assert draw.lighten(0b10000_010000_01000, 0b10000) == 0b11111_110000_11000
+    assert draw.lighten(0b01000_100000_01000, 0b10000) == 0b11000_111111_11000
+    assert draw.lighten(0b01000_010000_10000, 0b10000) == 0b11000_110000_11111
+
+def test_darken(draw):
+    assert draw.darken(0b00001_000010_00001, 0b00001) == 0b00000_000000_00000
+    assert draw.darken(0b00010_000100_00010         ) == 0b00001_000010_00001
+    assert draw.darken(0b00010_000100_00010, 0b00001) == 0b00001_000010_00001
+    assert draw.darken(0b10000_010000_00100, 0b00001) == 0b01111_001110_00011
+
+    assert draw.darken(0b00000_000000_00000, 0b00001) == 0b00000_000000_00000
+    assert draw.darken(0b00001_000001_00001, 0b00001) == 0b00000_000000_00000
+    assert draw.darken(0b10000_100000_10000, 0b10001) == 0b00000_000000_00000
+    assert draw.darken(0b10000_100010_10010, 0b10001) == 0b00000_000000_00001
+    assert draw.darken(0b10000_100100_10010, 0b10001) == 0b00000_000010_00001
+

wasp/draw565.py

@@ -10,6 +10,12 @@ import fonts.sans24
 import math
 import micropython
 
+from micropython import const
+
+R = const(0b11111_000000_00000)
+G = const(0b00000_111111_00000)
+B = const(0b00000_000000_11111)
+
 @micropython.viper
 def _bitblit(bitbuf, pixels, bgfg: int, count: int):
     mv = ptr16(bitbuf)
@@ -454,3 +460,48 @@ class Draw565(object):
         y1 = y - int(ydelta * r1)
 
         self.line(x0, y0, x1, y1, width, color)
+
+    def lighten(self, color, step=1):
+        """Get a lighter shade from the same palette.
+
+        The approach is somewhat unsophisticated. It is essentially just a
+        saturating add for each of the RGB fields.
+
+        :param color: Shade to lighten
+        :returns:     New colour
+        """
+        r = (color & R) + (step << 11)
+        if r > R:
+            r = R
+
+        g = (color & G) + (step <<  6)
+        if g > G:
+            g = G
+
+        b = (color & B) + step
+        if b > B:
+            b = B
+
+        return (r | g | b)
+
+    def darken(self, color, step=1):
+        """Get a darker shade from the same palette.
+
+        The approach is somewhat unsophisticated. It is essentially just a
+        desaturating subtract for each of the RGB fields.
+
+        :param color: Shade to darken
+        :returns:     New colour
+        """
+        rm = color & R
+        rs = step << 11
+        r = rm - rs if rm > rs else 0
+
+        gm = color & G
+        gs = step << 6
+        g = gm - gs if gm > gs else 0
+
+        bm = color & B
+        b = bm - step if bm > step else 0
+
+        return (r | g | b)