Fixed inconsistent default color in vp.write_svg().

The default color (from the default color scheme) for a layer would depend on whether previous layer would have their color specified on not. This is an inconsistent behaviour in itself, and it is inconsistent with the viewer's behaviour.

Also, the default color scheme as been moved to vpype/metadata.py.

CHANGELOG.md

@@ -9,7 +9,7 @@ New features and improvements:
 
   This feature is intended as a generic mechanism whereby a set of properties may be attached to specific layers (layer property) or all of them (global property). Properties are identified by a name and may be of arbitrary type (e.g. integer, floating point, color, etc.). This new infrastructure is used by several of the features introduced in this release, paves the way for future features, and further empowers plug-in writers. See the [documentation](https://vpype.readthedocs.io/en/latest/metadata) for more background information on metadata.
 
-* Layer color, pen width, and name are now customizable (#359)
+* Layer color, pen width, and name are now customizable (#359, #376)
   * The `read` commands now sets layer color, pen width, and name based on the input SVG if possible.
   * The new `color`, `penwdith`, and `name` commands can be used to modify layer color, pen width, and name.
   * The new `pens` command can apply a predefined or custom scheme on multiple layers at once. Two schemes, `rgb` and `cmyk`, are included and others may be defined in the configuration file.

vpype/io.py

@@ -18,6 +18,7 @@
 
 from .config import PaperConfig, PlotterConfig, config_manager
 from .metadata import (
+    METADATA_DEFAULT_COLOR_SCHEME,
     METADATA_FIELD_COLOR,
     METADATA_FIELD_NAME,
     METADATA_FIELD_PEN_WIDTH,
@@ -31,17 +32,6 @@
 __all__ = ["read_svg", "read_multilayer_svg", "write_svg", "write_hpgl"]
 
 
-_COLORS = [
-    "#00f",
-    "#080",
-    "#f00",
-    "#0cc",
-    "#0f0",
-    "#c0c",
-    "#cc0",
-    "black",
-]
-
 _DEFAULT_WIDTH = 1000
 _DEFAULT_HEIGHT = 1000
 
@@ -583,10 +573,16 @@ def write_svg(
         if color_mode == "layer" or (
             color_mode == "default" and not layer.property_exists(METADATA_FIELD_COLOR)
         ):
-            group.attribs["stroke"] = _COLORS[color_idx % len(_COLORS)]
+            group.attribs["stroke"] = METADATA_DEFAULT_COLOR_SCHEME[
+                color_idx % len(METADATA_DEFAULT_COLOR_SCHEME)
+            ]
             color_idx += 1
         elif color_mode == "default":
             group.attribs["stroke"] = str(layer.property(METADATA_FIELD_COLOR))
+
+            # we want to avoid a subsequent layer whose color is undefined to have its color
+            # affected by whether or not previous layer have their color defined
+            color_idx += 1
         elif color_mode == "none":
             group.attribs["stroke"] = "black"
         group.attribs["style"] = "display:inline"
@@ -612,7 +608,9 @@ def write_svg(
                 path = dwg.polyline((c.real, c.imag) for c in line)
 
             if color_mode == "path":
-                path.attribs["stroke"] = _COLORS[color_idx % len(_COLORS)]
+                path.attribs["stroke"] = METADATA_DEFAULT_COLOR_SCHEME[
+                    color_idx % len(METADATA_DEFAULT_COLOR_SCHEME)
+                ]
                 color_idx += 1
             group.add(path)
 

vpype/metadata.py

@@ -147,3 +147,15 @@ def __str__(self) -> str:
     "stroke-width",
     "text-rendering",
 }
+
+
+METADATA_DEFAULT_COLOR_SCHEME = [
+    Color("#00f"),
+    Color("#080"),
+    Color("#f00"),
+    Color("#0cc"),
+    Color("#0f0"),
+    Color("#c0c"),
+    Color("#cc0"),
+    Color("black"),
+]

vpype_viewer/engine.py

@@ -23,17 +23,6 @@
 from ._scales import DEFAULT_SCALE_SPEC, SCALES_MAP, ScaleSpec, UnitType
 from ._utils import ColorType, orthogonal_projection_matrix
 
-_COLORS: List[ColorType] = [
-    (0, 0, 1, 1),
-    (0, 0.5, 0, 1),
-    (1, 0, 0, 1),
-    (0, 0.75, 0.75, 1),
-    (0, 1, 0, 1),
-    (0.75, 0, 0.75, 1),
-    (0.75, 0.75, 0, 1),
-    (0, 0, 0, 1),
-]
-
 __all__ = ["DEFAULT_PEN_WIDTH", "DEFAULT_PEN_OPACITY", "ViewMode", "Engine"]
 
 DEFAULT_PEN_WIDTH = 1.1  # about 0.3mm
@@ -426,7 +415,9 @@ def _rebuild(self):
         if self._document is not None:
             color_index = 0
             for layer_id in sorted(self._document.layers):
-                layer_color: ColorType = _COLORS[color_index % len(_COLORS)]
+                layer_color: ColorType = vp.METADATA_DEFAULT_COLOR_SCHEME[
+                    color_index % len(vp.METADATA_DEFAULT_COLOR_SCHEME)
+                ].as_floats()
                 color_index += 1
 
                 lc = self._document.layers[layer_id]