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function splitBackgroundLayers(input: string): string[] {
const layers: string[] = [];
let depth = 0;
let start = 0;
for (let i = 0; i < input.length; i += 1) {
const ch = input[i] as string;
if (ch === "(") depth += 1;
else if (ch === ")") depth -= 1;
else if (ch === "," && depth === 0) {
layers.push(input.slice(start, i).trim());
start = i + 1;
}
}
layers.push(input.slice(start).trim());
return layers;
}
function parseColorStop(stop: string): { color: string; position?: number } {
const s = stop.trim();
// Handle functional colors like rgba(), rgb(), hsla(), hsl()
const colorFunctions = ["rgba(", "rgb(", "hsla(", "hsl("];
let color = "";
let remaining = "";
for (const fn of colorFunctions) {
if (s.startsWith(fn)) {
let depth = 0;
for (let i = 0; i < s.length; i += 1) {
const ch = s[i] as string;
if (ch === "(") depth += 1;
else if (ch === ")") {
depth -= 1;
if (depth === 0) {
color = s.slice(0, i + 1);
remaining = s.slice(i + 1).trim();
break;
}
}
}
break;
}
}
if (!color) {
const parts = s.split(/\s+/);
color = parts[0] as string;
remaining = parts.slice(1).join(" ");
}
// Convert transparent to transparent white for better blending
if (color === "transparent") {
color = "rgba(255, 255, 255, 0)";
}
// Parse position if present
let position: number | undefined;
if (remaining) {
const posMatch = remaining.match(/(\d+(?:\.\d+)?)%/);
if (posMatch) {
position = parseFloat(posMatch[1] as string) / 100;
}
}
return { color, position };
}
function parseLinearGradient(layer: string, width: number, height: number) {
const inside = layer.slice(layer.indexOf("(") + 1, layer.lastIndexOf(")"));
const parts = splitBackgroundLayers(inside);
const dir = (parts.shift() || "").trim();
let x0 = 0,
y0 = 0,
x1 = width,
y1 = 0; // default: to right
if (dir.endsWith("deg")) {
const deg = parseFloat(dir);
const rad = (deg * Math.PI) / 180;
const cx = width / 2;
const cy = height / 2;
const r = Math.hypot(width, height) / 2;
x0 = cx - Math.cos(rad) * r;
y0 = cy - Math.sin(rad) * r;
x1 = cx + Math.cos(rad) * r;
y1 = cy + Math.sin(rad) * r;
} else if (dir.startsWith("to ")) {
const d = dir.slice(3).trim();
if (d === "right") {
x0 = 0;
y0 = 0;
x1 = width;
y1 = 0;
} else if (d === "left") {
x0 = width;
y0 = 0;
x1 = 0;
y1 = 0;
} else if (d === "bottom") {
x0 = 0;
y0 = 0;
x1 = 0;
y1 = height;
} else if (d === "top") {
x0 = 0;
y0 = height;
x1 = 0;
y1 = 0;
}
} else {
// No direction specified, treat as first color
parts.unshift(dir);
}
return { x0, y0, x1, y1, colors: parts };
}
function parseRadialGradient(layer: string, width: number, height: number) {
const inside = layer.slice(layer.indexOf("(") + 1, layer.lastIndexOf(")"));
const parts = splitBackgroundLayers(inside);
const first = (parts.shift() || "").trim();
let cx = width / 2;
let cy = height / 2;
if (first.startsWith("circle at")) {
const pos = first.replace("circle at", "").trim();
const coords = pos.split(/\s+/);
for (let i = 0; i < coords.length; i += 1) {
const coord = coords[i] as string;
if (coord.endsWith("%")) {
const val = parseFloat(coord) / 100;
if (i === 0) cx = val * width;
else if (i === 1) cy = val * height;
} else if (coord === "left") cx = 0;
else if (coord === "right") cx = width;
else if (coord === "top") cy = 0;
else if (coord === "bottom") cy = height;
else if (coord === "center") {
if (i === 0) cx = width / 2;
else if (i === 1) cy = height / 2;
}
}
} else {
parts.unshift(first);
}
// Use farthest-corner for radius
const r = Math.max(
Math.hypot(cx, cy),
Math.hypot(width - cx, cy),
Math.hypot(cx, height - cy),
Math.hypot(width - cx, height - cy)
);
return { cx, cy, r, colors: parts };
}
export function drawCssBackground(
ctx: CanvasRenderingContext2D,
width: number,
height: number,
css: string
): void {
const layers = splitBackgroundLayers(css).filter(Boolean);
// Draw layers from last to first (CSS background order)
for (let i = layers.length - 1; i >= 0; i -= 1) {
const layer = layers[i] as string;
if (layer.startsWith("linear-gradient(")) {
const { x0, y0, x1, y1, colors } = parseLinearGradient(
layer,
width,
height
);
const grad = ctx.createLinearGradient(x0, y0, x1, y1);
const colorStops = colors.map((c) => parseColorStop(c as string));
// Handle positions properly
for (let j = 0; j < colorStops.length; j += 1) {
const stop = colorStops[j] as { color: string; position?: number };
const pos = stop.position ?? j / Math.max(1, colorStops.length - 1);
grad.addColorStop(Math.max(0, Math.min(1, pos)), stop.color);
}
ctx.fillStyle = grad;
ctx.fillRect(0, 0, width, height);
} else if (layer.startsWith("radial-gradient(")) {
const { cx, cy, r, colors } = parseRadialGradient(layer, width, height);
const grad = ctx.createRadialGradient(cx, cy, 0, cx, cy, r);
const colorStops = colors.map((c) => parseColorStop(c as string));
// Handle positions properly
for (let j = 0; j < colorStops.length; j += 1) {
const stop = colorStops[j] as { color: string; position?: number };
const pos = stop.position ?? j / Math.max(1, colorStops.length - 1);
grad.addColorStop(Math.max(0, Math.min(1, pos)), stop.color);
}
ctx.fillStyle = grad;
ctx.fillRect(0, 0, width, height);
} else if (
layer.startsWith("#") ||
layer.startsWith("rgb") ||
layer.startsWith("hsl") ||
layer === "transparent" ||
layer === "white" ||
layer === "black"
) {
if (layer !== "transparent") {
ctx.fillStyle = layer;
ctx.fillRect(0, 0, width, height);
}
}
}
}
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