colorLib: add buildCOLR and buildCPAL

Lib/fontTools/colorLib/builder.py

@@ -0,0 +1,54 @@
+from fontTools.ttLib import newTable
+from .errors import ColorLibError
+
+
+def buildCOLR(colorLayers):
+    """Build COLR table from color layers mapping.
+
+    Args:
+        colorLayers: Dict[str, List[Tuple[str, int]]]: map of base glyph names (str)
+            to lists of layer glyph names (str) and palette indices (int) tuples.
+
+    Return:
+        A new COLRv0 table.
+    """
+    from fontTools.ttLib.tables.C_O_L_R_ import LayerRecord
+
+    colorLayerLists = {}
+    for baseGlyphName, layers in colorLayers.items():
+        colorLayerLists[baseGlyphName] = [
+            LayerRecord(layerGlyphName, colorID) for layerGlyphName, colorID in layers
+        ]
+
+    colr = newTable("COLR")
+    colr.version = 0
+    colr.ColorLayers = colorLayerLists
+    return colr
+
+
+def buildCPAL(palettes):
+    """Build CPAL table from list of color palettes.
+
+    Args:
+        palettes: List[List[Tuple[float, float, float, float]]]: list of lists
+            colors encoded as tuples of (R, G, B, A) floats.
+
+    Return:
+        A new CPALv0 table.
+    """
+    from fontTools.ttLib.tables.C_P_A_L_ import Color
+
+    if len({len(p) for p in palettes}) != 1:
+        raise ColorLibError("color palettes have different lengths")
+    cpal = newTable("CPAL")
+    # TODO(anthotype): Support version 1 with palette types, labels and entry labels.
+    cpal.version = 0
+    cpal.numPaletteEntries = len(palettes[0])
+    cpal.palettes = [
+        [
+            Color(*(round(v * 255) for v in (blue, green, red, alpha)))
+            for red, green, blue, alpha in palette
+        ]
+        for palette in palettes
+    ]
+    return cpal

Lib/fontTools/colorLib/errors.py

@@ -0,0 +1,3 @@
+
+class ColorLibError(Exception):
+    pass