Add method to apply element viewBox

src/Svg/Tag/AbstractTag.php

@@ -189,6 +189,97 @@ protected function applyTransform($attributes)
         }
     }
 
+    /**
+     * Apply a viewBox transform to the element
+     *
+     * @param array $attributes
+     */
+    protected function applyViewbox($attributes) {
+        if (!isset($attributes["viewbox"])) {
+            return;
+        }
+
+        $surface = $this->document->getSurface();
+        $viewBox = preg_split('/[\s,]+/is', trim($attributes['viewbox']));
+        if (count($viewBox) != 4) {
+            return;
+        }
+
+        // Computing the equivalent transform of an SVG viewport
+        // https://svgwg.org/svg2-draft/coords.html#ComputingAViewportsTransform
+
+        // 1. Let vb-x, vb-y, vb-width, vb-height be the min-x, min-y, width and height values of the viewBox attribute respectively.
+        [$vbX, $vbY, $vbWidth, $vbHeight] = $viewBox;
+
+        if ($vbWidth < 0 || $vbHeight < 0) {
+            return;
+        }
+
+        // correct solution is to not render, for now scaling to 0 below
+        //if ($vbWidth == 0 || $vbHeight == 0) {
+        //}
+
+        // 2. Let e-x, e-y, e-width, e-height be the position and size of the element respectively.
+        $eX = $attributes["x"] ?? 0;
+        $eY = $attributes["y"] ?? 0;
+        $eWidth = $attributes["width"] ?? $this->document->getWidth();
+        $eHeight = $attributes["height"] ?? $this->document->getHeight();
+
+        // 3. Let align be the align value of preserveAspectRatio, or 'xMidYMid' if preserveAspectRatio is not defined.
+        $preserveAspectRatio = explode(" ", $attributes["preserveAspectRatio"] ?? "xMidYMid meet");
+        $align = $preserveAspectRatio[0];
+
+        // 4. Let meetOrSlice be the meetOrSlice value of preserveAspectRatio, or 'meet' if preserveAspectRatio is not defined or if meetOrSlice is missing from this value.
+        $meetOrSlice = $meetOrSlice ?? "meet";
+
+        // 5. Initialize scale-x to e-width/vb-width.
+        $scaleX = $vbWidth == 0 ? 0 : ($eWidth / $vbWidth);
+
+        // 6. Initialize scale-y to e-height/vb-height.
+        $scaleY = $vbHeight == 0 ? 0 : ($eHeight / $vbHeight);
+
+        // 7. If align is not 'none' and meetOrSlice is 'meet', set the larger of scale-x and scale-y to the smaller.
+        if ($align !== "none" && $meetOrSlice === "meet") {
+            $scaleX = min($scaleX, $scaleY);
+            $scaleY = min($scaleX, $scaleY);
+        }
+
+        // 8. Otherwise, if align is not 'none' and meetOrSlice is 'slice', set the smaller of scale-x and scale-y to the larger.
+        elseif ($align !== "none" && $meetOrSlice === "slice") {
+            $scaleX = max($scaleX, $scaleY);
+            $scaleY = max($scaleX, $scaleY);
+        }
+
+        // 9. Initialize translate-x to e-x - (vb-x * scale-x).
+        $translateX = $eX - ($vbX * $scaleX);
+
+        // 10. Initialize translate-y to e-y - (vb-y * scale-y)
+        $translateY = $eY - ($vbY * $scaleY);
+
+        // 11. If align contains 'xMid', add (e-width - vb-width * scale-x) / 2 to translate-x.
+        if (strpos($align, "xMid") !== false) {
+            $translateX += ($eWidth - $vbWidth * $scaleX) / 2;
+        }
+
+        // 12. If align contains 'xMax', add (e-width - vb-width * scale-x) to translate-x.
+        if (strpos($align, "xMax") !== false) {
+            $translateX += ($eWidth - $vbWidth * $scaleX);
+        }
+
+        // 13. If align contains 'yMid', add (e-height - vb-height * scale-y) / 2 to translate-y.
+        if (strpos($align, "yMid") !== false) {
+            $translateX += ($eHeight - $vbHeight * $scaleY) / 2;
+        }
+
+        // 14. If align contains 'yMax', add (e-height - vb-height * scale-y) to translate-y.
+        if (strpos($align, "yMid") !== false) {
+            $translateX += ($eHeight - $vbHeight * $scaleY);
+        }
+
+        $surface->translate($translateX, $translateY);
+        $surface->scale($scaleX, $scaleY);
+    }
+
     /**
      * Convert the given size for the context of this current tag.
      * Takes a pixel-based reference, which is usually specific to the context of the size,