add clipping js code

lib/extract/extractViewbox.js

@@ -0,0 +1,71 @@
+export default function({viewbox, width, height, preserveAspectRatio, x: dx, y: dy, dScale, dScaleX, dScaleY, shouldTransform}) {
+    if (!viewbox || !width || !height) {
+        return false;
+    }
+
+    if (typeof viewbox === 'string') {
+        let parts = viewbox.trim().split(/\s+/);
+        let vw = +parts[2];
+        let vh = +parts[3];
+
+        // width or height can`t be negative
+        if (vw < 0 || vh < 0 || parts.length !== 4) {
+            return false;
+        }
+
+        // width or height equals zero disable render
+        if (!vw || !vh) {
+            return {
+                x: 0,
+                y: 0,
+                scaleX: 0,
+                scaleY: 0
+            }
+        }
+
+        let vx = +parts[0] || 0;
+        let vy = +parts[1] || 0;
+        let preserve = preserveAspectRatio !== 'none';
+        let scaleX = 1;
+        let scaleY = 1;
+        let x = 0;
+        let y = 0;
+        let sx = width / vw;
+        let sy = height / vh;
+        if (preserve) {
+            scaleX = scaleY = Math.min(sx, sy);
+            x = width / 2 - Math.min(vw, vh) * scaleX / 2 - vx * scaleX;
+            y = 0 - vy * scaleX;
+
+            if (sx < sy) {
+                [x, y] = [y, x];
+            }
+        } else {
+            scaleX = sx;
+            scaleY = sy;
+            x = -vx * sx;
+            y = -vy * sy;
+        }
+
+        if (shouldTransform) {
+            x += (+dx || 0);
+            y += (+dy || 0);
+
+            if (dScale) {
+                scaleX *= (+dScale || 1);
+                scaleY *= (+dScale || 1);
+            } else {
+                scaleX *= (+dScaleX || 1);
+                scaleY *= (+dScaleY || 1);
+            }
+        }
+
+        return {
+            x,
+            y,
+            scaleX,
+            scaleY
+        };
+    }
+    return false;
+}