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import type { ScaleGradientFunction } from '../hooks/use-scale-gradient';
import type uPlot from 'uplot';
export default function getGradientFill(
fillColorFrom: string,
fillColorTo: string,
scaleGradient: ScaleGradientFunction
): ( self: uPlot, seriesIdx: number ) => CanvasRenderingContext2D[ 'fillStyle' ] {
return ( u, seriesIdx ) => {
// Find min and max values for the visible parts of all y axis' and map it to color values to draw a gradient.
const s = u.series[ seriesIdx ]; // data set
const sc = u.scales[ s.scale || 1 ]; // y axis values
// if values are not initialised default to a solid color
if ( s.min === Infinity || s.max === -Infinity ) {
return fillColorFrom;
}
let min = Infinity;
let max = -Infinity;
// get in-view y range for this scale
u.series.forEach( ( ser ) => {
if ( ser.show && ser.scale === s.scale ) {
min = Math.min( min, ser.min || 0 );
max = Math.max( max, ser.max || 0 );
}
} );
let range = max - min;
// if `range` from data is 0, apply axis range
if ( range === 0 ) {
range = sc?.max !== undefined && sc?.min !== undefined ? sc.max - sc.min : 0;
min = sc?.min || 0;
}
return scaleGradient( u, s.scale || 'y', 1, [
[ min + range * 0.0, fillColorTo ],
[ min + range * 1.0, fillColorFrom ],
] );
};
}
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