Line overlay (with area)

[ze2j]

Proposal

Here is a sketch of what it could look like:

class_name TauLineConfig extends TauPaneOverlayConfig

enum LineMode
{
	INDEPENDENT,    ## Each series is drawn independently. Lines at the same X may overlap.
	STACKED         ## Series values are summed along Y so each line sits on top of the previous.
}
@export var mode: LineMode = LineMode.INDEPENDENT

## Normalization applied to stacked line sums when mode is STACKED.
@export var stacked_normalization: StackedNormalization = StackedNormalization.NONE

enum InterpolationMode
{
	LINEAR,             ## Straight segment between consecutive samples.
	STEP_BEFORE,        ## Vertical jump first, then horizontal. Y changes at the previous X.
	STEP_AFTER,         ## Horizontal first, then vertical jump. Y changes at the next X.
	STEP_MIDDLE,        ## Jump at the midpoint between the two X positions.
	SMOOTH_MONOTONE     ## Fritsch-Carlson monotone cubic, no overshoot between samples.
}
@export var interpolation_mode: InterpolationMode = InterpolationMode.LINEAR


enum GapPolicy
{
	SKIP,      ## The curve breaks at any NaN or infinite sample.
	BRIDGE     ## Invalid samples are dropped and neighbors are connected directly.
}
## Strategy applied when a sample has an invalid X or Y value.
@export var gap_policy: GapPolicy = GapPolicy.SKIP


enum FillMode
{
	NONE,           ## No area is filled.
	TO_BASELINE,    ## Fill between the line and a configurable constant baseline.
	STACKED         ## Each stacked layer is filled down to the layer below.
}
## Strategy applied to fill the area between the line and a baseline.
@export var fill_mode: FillMode = FillMode.NONE

## Reference Y value used when fill_mode is TO_BASELINE.
@export var fill_baseline: float = 0.0

@export var hover_max_distance_px: int = 10

## Visual style applied to this overlay. Never null.
@export var style: TauLineStyle = TauLineStyle.new()

var line_visual_callbacks: LineVisualCallbacks:
	get:
		return visual_callbacks as LineVisualCallbacks
	set(value):
		visual_callbacks = value


func _init() -> void:
	overlay_type = PaneOverlayType.LINE

And the style:

class_name TauLineStyle extends Resource

## Line widths in pixels in the normal state per series index.
@export var line_widths_px: Array[float] = [2.0]

## Line width in pixels for the two segments adjacent to the hovered sample.
@export var hovered_line_width_px: float = 3.0

## Dash lengths in pixels per series index. Zero means solid.
@export var dash_lengths_px: Array[int] = [0]

## Flat fill color. Color(0, 0, 0, 0) means "use the series color".
@export var fill_color: Color = Color(0, 0, 0, 0)

## Multiplier applied to the fill alpha channel.
@export var fill_alpha: float = 0.2

## Texture sampled across the fill area. Null disables texture fill.
@export var fill_texture: Texture2D = null

## Number of times fill_texture repeats across the reference frame.
@export var fill_texture_tiling: Vector2 = Vector2(1, 1)

## UV translation applied to fill_texture after tiling.
@export var fill_texture_offset: Vector2 = Vector2(0, 0)

## Rotation in degrees applied to fill_texture around UV (0.5, 0.5).
@export var fill_texture_rotation_deg: float = 0.0

enum FillAnchor
{
	PANE_RECT,      ## Reference frame is the pane rectangle in pixels.
	FILL_BOUNDS,    ## Reference frame is the bounding box of the filled polygon in pixels.
	DATA_DOMAIN     ## Reference frame is the visible data domain in data coordinates.
}
## Reference frame used by fill_texture.
@export var fill_anchor: FillAnchor = FillAnchor.PANE_RECT

VisualAttributes carries only the inherited buffers color_buffer and alpha_buffer.

At draw time the final fill color is resolved in this order:

• fill_texture if non-null.
• fill_color if different from Color(0, 0, 0, 0)
• else series color from TauXYStyle.series_colors

Whatever survives has its alpha channel multiplied by fill_alpha before rendering.

Edits:

1. changed dash_px scalar to dash_lengths_px array (indexed by series index)
2. changed line_width_px scalar to line_widths_px array (indexed by series index)