/** * Determine if a page break is allowed before $frame * http://www.w3.org/TR/CSS21/page.html#allowed-page-breaks * * In the normal flow, page breaks can occur at the following places: * * 1. In the vertical margin between block boxes. When a page * break occurs here, the used values of the relevant * 'margin-top' and 'margin-bottom' properties are set to '0'. * 2. Between line boxes inside a block box. * * These breaks are subject to the following rules: * * * Rule A: Breaking at (1) is allowed only if the * 'page-break-after' and 'page-break-before' properties of * all the elements generating boxes that meet at this margin * allow it, which is when at least one of them has the value * 'always', 'left', or 'right', or when all of them are * 'auto'. * * * Rule B: However, if all of them are 'auto' and the * nearest common ancestor of all the elements has a * 'page-break-inside' value of 'avoid', then breaking here is * not allowed. * * * Rule C: Breaking at (2) is allowed only if the number of * line boxes between the break and the start of the enclosing * block box is the value of 'orphans' or more, and the number * of line boxes between the break and the end of the box is * the value of 'widows' or more. * * * Rule D: In addition, breaking at (2) is allowed only if * the 'page-break-inside' property is 'auto'. * * If the above doesn't provide enough break points to keep * content from overflowing the page boxes, then rules B and D are * dropped in order to find additional breakpoints. * * If that still does not lead to sufficient break points, rules A * and C are dropped as well, to find still more break points. * * We will also allow breaks between table rows. However, when * splitting a table, the table headers should carry over to the * next page (but they don't yet). * * @param Frame $frame the frame to check * * @return bool true if a break is allowed, false otherwise */ protected function _page_break_allowed(Frame $frame) { $block_types = array("block", "list-item", "table", "-dompdf-image"); Helpers::dompdf_debug("page-break", "_page_break_allowed(" . $frame->get_node()->nodeName . ")"); $display = $frame->get_style()->display; // Block Frames (1): if (in_array($display, $block_types)) { // Avoid breaks within table-cells if ($this->_in_table) { Helpers::dompdf_debug("page-break", "In table: " . $this->_in_table); return false; } // Rules A & B if ($frame->get_style()->page_break_before === "avoid") { Helpers::dompdf_debug("page-break", "before: avoid"); return false; } // Find the preceeding block-level sibling $prev = $frame->get_prev_sibling(); while ($prev && !in_array($prev->get_style()->display, $block_types)) { $prev = $prev->get_prev_sibling(); } // Does the previous element allow a page break after? if ($prev && $prev->get_style()->page_break_after === "avoid") { Helpers::dompdf_debug("page-break", "after: avoid"); return false; } // If both $prev & $frame have the same parent, check the parent's // page_break_inside property. $parent = $frame->get_parent(); if ($prev && $parent && $parent->get_style()->page_break_inside === "avoid") { Helpers::dompdf_debug("page-break", "parent inside: avoid"); return false; } // To prevent cascading page breaks when a top-level element has // page-break-inside: avoid, ensure that at least one frame is // on the page before splitting. if ($parent->get_node()->nodeName === "body" && !$prev) { // We are the body's first child Helpers::dompdf_debug("page-break", "Body's first child."); return false; } // If the frame is the first block-level frame, use the value from // $frame's parent instead. if (!$prev && $parent) { return $this->_page_break_allowed($parent); } Helpers::dompdf_debug("page-break", "block: break allowed"); return true; } else { if (in_array($display, Style::$INLINE_TYPES)) { // Avoid breaks within table-cells if ($this->_in_table) { Helpers::dompdf_debug("page-break", "In table: " . $this->_in_table); return false; } // Rule C $block_parent = $frame->find_block_parent(); if (count($block_parent->get_line_boxes()) < $frame->get_style()->orphans) { Helpers::dompdf_debug("page-break", "orphans"); return false; } // FIXME: Checking widows is tricky without having laid out the // remaining line boxes. Just ignore it for now... // Rule D $p = $block_parent; while ($p) { if ($p->get_style()->page_break_inside === "avoid") { Helpers::dompdf_debug("page-break", "parent->inside: avoid"); return false; } $p = $p->find_block_parent(); } // To prevent cascading page breaks when a top-level element has // page-break-inside: avoid, ensure that at least one frame with // some content is on the page before splitting. $prev = $frame->get_prev_sibling(); while ($prev && ($prev->is_text_node() && trim($prev->get_node()->nodeValue) == "")) { $prev = $prev->get_prev_sibling(); } if ($block_parent->get_node()->nodeName === "body" && !$prev) { // We are the body's first child Helpers::dompdf_debug("page-break", "Body's first child."); return false; } // Skip breaks on empty text nodes if ($frame->is_text_node() && $frame->get_node()->nodeValue == "") { return false; } Helpers::dompdf_debug("page-break", "inline: break allowed"); return true; // Table-rows } else { if ($display === "table-row") { // Simply check if the parent table's page_break_inside property is // not 'avoid' $p = Table::find_parent_table($frame); while ($p) { if ($p->get_style()->page_break_inside === "avoid") { Helpers::dompdf_debug("page-break", "parent->inside: avoid"); return false; } $p = $p->find_block_parent(); } // Avoid breaking after the first row of a table if ($p && $p->get_first_child() === $frame) { Helpers::dompdf_debug("page-break", "table: first-row"); return false; } // If this is a nested table, prevent the page from breaking if ($this->_in_table > 1) { Helpers::dompdf_debug("page-break", "table: nested table"); return false; } Helpers::dompdf_debug("page-break", "table-row/row-groups: break allowed"); return true; } else { if (in_array($display, Table::$ROW_GROUPS)) { // Disallow breaks at row-groups: only split at row boundaries return false; } else { Helpers::dompdf_debug("page-break", "? " . $frame->get_style()->display . ""); return false; } } } } }